Quarterly Financial Data (Unaudited) (Details) - 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, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Impairment charges and other																	$ (600)	$ 1,300	$ 9,800	$ 0	$ 0	$ 10,480
Selected Quarterly Financial Information [Abstract]
Revenues	$ 826,494		$ 795,513		$ 795,552		$ 882,664		$ 729,069		$ 702,538		$ 707,332		$ 802,408					3,300,223	2,941,347	2,603,614
Gross profit	142,866		139,966		130,553		159,346		110,539		117,796		113,259		150,016					572,731	491,610	437,867
Operating income	23,712		29,799		22,938		53,492		14,467		22,773		16,023		53,043					129,941	106,306	65,699
Net income	$ 15,554		$ 19,202		$ 14,018		$ 35,628		$ 9,520		$ 14,065		$ 9,713		$ 32,693					$ 84,402	$ 65,991	$ 39,390
Basic net income per share of common stock (in dollars per share)	$ 0.36	[1]	$ 0.46	[1]	$ 0.34	[1]	$ 0.85	[1]	$ 0.23	[1]	$ 0.33	[1]	$ 0.23	[1]	$ 0.77	[1]				$ 2.02	$ 1.55	$ 0.79
Diluted net income per share (in dollars per share)	$ 0.36	[1]	$ 0.46	[1]	$ 0.33	[1]	$ 0.85	[1]	$ 0.23	[1]	$ 0.33	[1]	$ 0.23	[1]	$ 0.77	[1]				$ 2.01	$ 1.54	$ 0.79

[1] (1) Adjusted to reflect the two-for-one split of our common stock effected on December 18, 2017 as a stock dividend.