Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data (Unaudited)
Revenue	$ 588,359	$ 594,536	$ 535,043	$ 464,941	$ 461,072	$ 480,851	$ 465,411	$ 380,588	$ 2,182,879	$ 1,787,922	$ 1,634,340
Gross Profit	118,175	127,868	111,183	89,053	93,731	100,858	95,738	75,954	446,279	366,281	344,009
Net income	$ 25,156	$ 38,541	$ 32,547	$ 16,659	$ 7,539	$ 22,284	$ 17,972	$ 7,477	$ 112,903	$ 55,272	$ 64,896
Basic-
Basic (in dollars per share)	$ 0.68	$ 1.03	$ 0.87	$ 0.45	$ 0.20	$ 0.60	$ 0.48	$ 0.20	$ 3.03	$ 1.48	$ 1.74
Diluted-
Diluted (in dollars per share)	$ 0.67	$ 1.02	$ 0.87	$ 0.44	$ 0.20	$ 0.59	$ 0.48	$ 0.20	$ 3.00	$ 1.47	$ 1.72
Increase to provision for income taxes					$ 9,500					$ 9,500