Treasury Shares, Etc.
| Concept | 
                                    
                                        As at 2023-12-31  | 
                            
                                
                                    
                                        As at 2023-12-31  | 
                            
                                
                                    
                                        As at 2023-12-31  | 
                            
                                
                                    
                                        As at 2023-12-31  | 
                            
                                
                                    
                                        As at 2023-12-31  | 
                            
                        
|---|---|---|---|---|---|
| Treasury shares, etc. | |||||
| Treasury shares, etc. | |||||
| Name of shareholder | — | 
                                        
                                             
                                                笹島建設株式会社
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                株式会社熊谷組
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                共栄機械工事株式会社
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                株式会社前田工務店
                                                
                                             
                                        
                                     | 
                                
                            
| Address of shareholder | — | 
                                        
                                             
                                                東京都港区南青山2丁目22番3号
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                福井県福井市中央2丁目6番8号
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                神奈川県鎌倉市岩瀬1丁目21番7号
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                東京都江東区東砂5丁目5番10号
                                                
                                             
                                        
                                     | 
                                
                            
| Number of shares held in own name | 
                                        
                                             
                                                832,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                212,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                542,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                75,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                2,700
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Number of shares held in others' names | 
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Total number of shares held | 
                                        
                                             
                                                832,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                212,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                542,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                75,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                2,700
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Shareholding ratio | 
                                        
                                             
                                                0.0190
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.0048
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.0124
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.0017
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.0001
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     |