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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Nov. 30, 2018
Jan. 31, 2018
Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]          
Equity method ownership percentage in joint venture 49.00%        
Cash and cash equivalents maturity description 90        
Additional amounts to be paid in cash or common stock based on achievement of performance measures within period, maximum years 5 years        
Money market funds fair value $ 0.5 $ 9.2      
Cash surrender fair value of life insurance 10.5 15.6      
Contingent consideration liabilities related to acquisitions $ 20.0 $ 30.5      
5.25% Senior Unsecured Notes Due 2023 [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Debt instrument interest rate 5.25%       5.25%
6.25% Senior Unsecured Notes Due 2027 [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Debt instrument interest rate 6.25%   6.25%    
Unnamed Corporate Joint Venture [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Equity method ownership percentage in joint venture 37.50%     49.00%  
Government Contracts Concentration Risk [Member] | Accounts Receivable [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Percentage of net accounts receivable 19.00% 17.00%      
Buildings [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 30 years        
Maximum [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Long-term investments maturity period, in years 5 years        
Short-Term investments maturity period, in years 1 year        
Intangible assets finite lives 20 years        
Maximum [Member] | Medical Equipment [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 7 years        
Maximum [Member] | Computer Equipment [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 7 years        
Maximum [Member] | Software and Software Development Costs [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 7 years        
Maximum [Member] | Furniture [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 7 years        
Minimum [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Long-term investments maturity period, in years 1 year        
Intangible assets finite lives 1 year        
Minimum [Member] | Medical Equipment [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 3 years        
Minimum [Member] | Computer Equipment [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 3 years        
Minimum [Member] | Software and Software Development Costs [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 3 years        
Minimum [Member] | Furniture [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Property and equipment estimated useful lives, years 3 years