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Commitments and Contingencies - Additional Information (Details)
 1 Months Ended 12 Months Ended
Nov. 30, 2020
businessUnit
Feb. 28, 2014
people
Dec. 31, 2020
USD ($)
facility
Dec. 31, 2020
GBP (£)
facility
Dec. 31, 2019
USD ($)
Dec. 31, 2019
GBP (£)
Dec. 31, 2018
USD ($)
Dec. 31, 2020
GBP (£)
Jul. 31, 2017
USD ($)
Loss Contingencies [Line Items]                  
Capital expenditure commitments     $ 1,100,000   $ 1,000,000.0   $ 2,500,000    
Long-term debt, gross     $ 54,100,000            
Number of bonding facilities | facility     2 2          
Individuals with minor injuries | people   3              
Number of lawsuits | businessUnit 3                
Committed Banking Facilities                  
Loss Contingencies [Line Items]                  
Debt maximum borrowing capacity     $ 150,000,000.0   150,000,000.0        
Letter of Credit                  
Loss Contingencies [Line Items]                  
Debt maximum borrowing capacity     1,300,000         £ 1,000,000.0  
Revolving credit facility                  
Loss Contingencies [Line Items]                  
Debt maximum borrowing capacity                 $ 150,000,000
Long-term debt, gross     $ 4,100,000   17,500,000        
GBP                  
Loss Contingencies [Line Items]                  
Number of bonding facilities | facility     1 1          
GBP | Bonding Facility For Bank Guarantees                  
Loss Contingencies [Line Items]                  
Debt maximum borrowing capacity     $ 6,100,000   5,900,000     £ 4,500,000  
Amount drawn/utilized     $ 1,400,000 £ 1,000,000.0 2,300,000 £ 1,600,000      
U.S. dollars                  
Loss Contingencies [Line Items]                  
Number of bonding facilities | facility     1 1          
U.S. dollars | Bonding Facility For Bank Guarantees                  
Loss Contingencies [Line Items]                  
Debt maximum borrowing capacity     $ 1,500,000   $ 400,000        
Amount drawn/utilized     $ 800,000