Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected Quarterly Financial Data
Revenue	$ 698,961	$ 714,099	$ 743,468	$ 700,131	$ 719,584	$ 706,918	$ 650,302	$ 538,473	$ 2,856,659	$ 2,615,277	$ 2,182,879
Gross Profit	136,999	147,196	145,695	117,093	132,560	142,702	120,016	106,665	546,983	501,943	446,279
Net income	$ 42,840	$ 50,088	$ 39,495	$ 17,716	$ 34,052	$ 36,233	$ 24,173	$ 19,866	$ 150,139	$ 114,324	$ 112,903
Basic-
Basic (in dollars per share)	$ 1.18	$ 1.37	$ 1.08	$ 0.48	$ 0.93	$ 0.98	$ 0.65	$ 0.54	$ 4.11	$ 3.10	$ 3.03
Diluted-
Diluted (in dollars per share)	$ 1.17	$ 1.36	$ 1.08	$ 0.48	$ 0.92	$ 0.98	$ 0.65	$ 0.53	$ 4.09	$ 3.08	$ 3.00
Gain due to insurance proceeds received					$ 4,800