Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 08, 2015
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents maturity description	90 days or less
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	$ 12.4	$ 13.9
Cash surrender fair value of life insurance	15.8	14.5
Contingent consideration liabilities related to acquisitions, fair value	$ 17.3	$ 24.9
5.25% Senior Unsecured Notes Due 2023 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument interest rate			5.25%
Variable Interest Entity, Primary Beneficiary [Member]
Summary Of Significant Accounting Policies [Line Items]
Consolidation method ownership percentage in joint venture	75.00%
Unnamed Corporate Joint Venture [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method ownership percentage in joint venture	37.50%
Government Contracts Concentration Risk [Member] | Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of net accounts receivable	17.00%	19.00%
Buildings [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives, years	20 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Long-term investments maturity period, in years	7 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