Acquisitions - Additional Information (Detail) - USD ($) |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Business Acquisition [Line Items] | |||
Goodwill | $ 713,811,000 | $ 414,936,000 | |
Goodwill, expected tax deductible amount | 0 | ||
Acquisition-related expenses | 17,300,000 | 1,200,000 | $ 9,800,000 |
Byram Healthcare | |||
Business Acquisition [Line Items] | |||
Combined consideration, net of cash acquired | 367,000,000 | ||
Goodwill | 288,691,000 | ||
Domestic | |||
Business Acquisition [Line Items] | |||
Goodwill | 468,697,000 | $ 180,006,000 | |
Domestic | Byram Healthcare | |||
Business Acquisition [Line Items] | |||
Goodwill | $ 289,000,000 | ||
Minimum | |||
Business Acquisition [Line Items] | |||
Acquired intangible assets , useful life | 3 years | ||
Maximum | |||
Business Acquisition [Line Items] | |||
Acquired intangible assets , useful life | 10 years |