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Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]      
Reserve for uncollectible accounts $ 8.3 $ 6.9  
Accrual for estimated claims 32.1 $ 20.0  
State tax net operating losses, valuation allowance 0.1    
Federal and State [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Incentive tax credit carryforwards $ 6.4    
Software Development [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Intangible assets estimated useful life 10 years    
Leasehold Improvements [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment estimated life, description the shorter of useful life or lease term    
Minimum [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Ownership percentage 50.00%    
Maximum [Member] | Customer Concentration Risk [Member] | Revenue [Member] | Service [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Minimum percentage of revenue accounted for by one customer 10.00% 10.00% 10.00%
Maximum [Member] | Building And Improvement [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment estimated life 40 years    
Maximum [Member] | Computer Equipment and Software [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment estimated life 10 years    
Maximum [Member] | Furniture and Equipment [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment estimated life 10 years    
Maximum [Member] | Transportation Equipment [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment estimated life 16 years