Supplemental Cash Flows Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Supplemental disclosure of cash flow data:
Interest paid	$ 37,819	$ 42,617
Income taxes paid, net of refunds	5,672	8,249
Supplemental disclosure of noncash investing and financing activities:
Contingent consideration payable	6,400	3,564
Contingent consideration settled with the issuance of Class A common stock	$ 771
Deferred purchase price		$ 71,200