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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 |  |  |  |

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