Selected Quarterly Financial Data (Unaudited) - Summary of Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 1,162,576	$ 1,054,360	$ 924,513	$ 893,448	$ 978,560	$ 932,814	$ 855,557	$ 805,859	$ 4,034,897	$ 3,572,790	$ 3,525,595
Gross margin	138,091	116,524	101,317	101,585	120,454	111,454	114,490	108,387	457,517	454,785	412,695
Operating income	41,127	21,669	16,578	17,177	30,839	29,855	34,297	28,843	96,551	123,834	117,030
Net income	$ 99,943	$ 15,334	$ 9,542	$ 10,334	$ 18,244	$ 17,924	$ 20,671	$ 17,965	$ 135,153	$ 74,805	$ 70,949
Basic earnings per share	$ 3.01	$ 0.46	$ 0.29	$ 0.31	$ 0.55	$ 0.54	$ 0.61	$ 0.51	$ 4.07	$ 2.21	$ 1.98
Diluted earnings per share	$ 2.99	$ 0.46	$ 0.29	$ 0.31	$ 0.55	$ 0.54	$ 0.61	$ 0.51	$ 4.05	$ 2.20	$ 1.97