Acquisitions - Pro Forma Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Revenues, as reported	$ 794,954	$ 768,982	$ 789,353	$ 854,427	$ 821,199	$ 767,694	$ 769,049	$ 821,814	$ 3,207,716	$ 3,179,756	$ 2,695,033
Net earnings, as reported	$ 21,631	$ 29,464	$ 38,501	$ 49,687	$ 21,726	$ 24,194	$ 40,546	$ 49,243	$ 139,283	$ 135,709	78,233
Progressive
Business Acquisition [Line Items]
Revenues, pro forma											2,851,631
Net earnings, pro forma											$ 86,038