Statement Of Cash Flows [Abstract]
| Concept | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | 2021-01-01 to 2021-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | 2020-01-01 to 2020-12-31 | As at 2019-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of cash flows [abstract] | |||||||||||||||||||||
| Cash flows from (used in) operating activities [abstract] | |||||||||||||||||||||
| Profit (loss) | 
                                                9,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                26,965,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                26,965,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                26,956,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                20,834,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                20,880,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                46,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                20,880,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Adjustments to reconcile profit (loss) [abstract] | |||||||||||||||||||||
| Adjustments for losses (gains) on disposal of non-current assets | — | — | — | — | — | — | — | — | — | 
                                                539,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                2,930,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Other adjustments to reconcile profit (loss) | — | — | — | — | — | — | — | — | — | 
                                                24,903,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                18,249,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Income taxes paid (refund), classified as operating activities | — | — | — | — | — | — | — | — | — | 
                                                2,023,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                3,573,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Cash flows from (used in) operating activities | — | — | — | — | — | — | — | — | — | 
                                                289,866,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                194,961,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Cash flows from (used in) investing activities [abstract] | |||||||||||||||||||||
| Other cash payments to acquire equity or debt instruments of other entities, classified as investing activities | — | — | — | — | — | — | — | — | — | 
                                                224,349,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                106,262,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Proceeds from sales of property, plant and equipment, classified as investing activities | — | — | — | — | — | — | — | — | — | 
                                                624,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                2,865,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Purchase of property, plant and equipment, classified as investing activities | — | — | — | — | — | — | — | — | — | 
                                                6,958,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                3,531,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Cash flows from (used in) investing activities | — | — | — | — | — | — | — | — | — | 
                                                230,683,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                106,928,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Cash flows from (used in) financing activities [abstract] | |||||||||||||||||||||
| Payments of lease liabilities, classified as financing activities | — | — | — | — | — | — | — | — | — | 
                                                13,416,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                12,504,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Interest paid, classified as financing activities | — | — | — | — | — | — | — | — | — | 
                                                721,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                1,130,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Cash flows from (used in) financing activities | — | — | — | — | — | — | — | — | — | 
                                                14,137,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                13,634,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Increase (decrease) in cash and cash equivalents after effect of exchange rate changes | — | — | — | — | — | — | — | — | — | 
                                                45,046,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                74,399,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Cash and cash equivalents | — | — | 
                                                2,142,718,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,097,672,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | — | — | — | 
                                                2,023,273,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             |