Acquisitions - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets acquired:
Goodwill	$ 490,607	$ 484,941
Select and BSL
Assets acquired:
Cash	88
Accounts receivable	6,084
Other receivables	2,023
Inventories	2,588
Prepaid and other current assets	29
Property and equipment	605
Goodwill	4,943
Intangible assets	8,933
Total assets acquired	25,293
Liabilities assumed:
Accounts payable	(3,122)
Accrued expenses and other current liabilities	(160)
Total liabilities assumed	(3,282)
Total net assets acquired	$ 22,011