Unaudited Quarterly Financial Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 577,517	$ 572,123	$ 485,323	$ 430,045	$ 441,023	$ 442,443	$ 434,424	$ 406,851	$ 2,065,008	$ 1,724,741	$ 1,523,101
Gross profit	192,932	191,404	158,534	135,875	142,537	144,838	141,905	128,155	678,745	557,435	454,875
Income from continuing operations	19,173	24,891	14,335	13,023	19,526	20,723	19,641	13,605	71,422	73,495	51,140
Net income	$ 19,338	$ 24,925	$ 14,252	$ 39,135	$ 20,473	$ 22,005	$ 20,789	$ 13,917	$ 97,650	$ 77,184	$ 84,512
Earnings Per Share, Basic [Abstract]
Continuing operations	$ 0.36	$ 0.47	$ 0.28	$ 0.25	$ 0.38	$ 0.39	$ 0.36	$ 0.25	$ 1.37	$ 1.38	$ 0.96
Discontinued operations	0.01	0.00	(0.01)	0.51	0.01	0.02	0.02	0.01	0.50	0.06	0.62
Net income	0.37	0.47	0.27	0.76	0.39	0.41	0.38	0.26	1.87	1.44	1.58
Earnings Per Share, Diluted [Abstract]
Continuing operations	0.36	0.47	0.27	0.25	0.37	0.38	0.36	0.25	1.35	1.35	0.94
Discontinued operations	0.00	0.00	0.00	0.50	0.02	0.03	0.02	0.00	0.49	0.07	0.61
Net income	$ 0.36	$ 0.47	$ 0.27	$ 0.75	$ 0.39	$ 0.41	$ 0.38	$ 0.25	$ 1.84	$ 1.42	$ 1.55
Segment Reporting Information
Income from discontinued operations, net of income taxes									$ 525	$ 3,689	$ 2,532
Discontinued Operations, Disposed of by Sale [Member]
Segment Reporting Information
Income from discontinued operations, net of income taxes	$ 165	$ 34	$ (83)	$ 26,112	$ 947	$ 1,282	$ 1,148	$ 312	$ 26,228	$ 3,689