Supplemental Cash Flows Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Supplemental disclosure of cash flow data:
Interest paid	$ 28,710	$ 28,327
Income taxes paid, net of refunds	3,474	4,451
Supplemental disclosure of noncash investing and financing activities:
Contingent consideration payable	5,900	3,564
Contingent consideration settled with the issuance of Class A common stock	$ 771
Deferred purchase price		$ 71,200