Acquisitions - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets acquired:
Goodwill	$ 490,315	$ 484,941
Select and BSL
Assets acquired:
Cash	88
Accounts receivable	6,095
Other receivables	2,012
Inventories	2,612
Prepaid and other current assets	29
Property and equipment	605
Goodwill	5,019
Intangible assets	8,953
Total assets acquired	25,413
Liabilities assumed:
Accounts payable	(3,125)
Accrued expenses and other current liabilities	(318)
Total liabilities assumed	(3,443)
Total net assets acquired	$ 21,970