Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Revenue	$ 2,222,107	$ 2,136,074	$ 1,988,454
Cost of revenue	1,478,642	1,439,691	1,344,035
Gross profit	743,465	696,383	644,419
Operating expenses:
Selling, general and administrative	508,030	452,318	399,700
Depreciation and amortization	58,520	41,237	32,279
Total operating expenses	566,550	493,555	431,979
Income from operations	176,915	202,828	212,440
Interest expense, net, and other	28,427	16,143	19,677
Income before income taxes	148,488	186,685	192,763
Income tax expense	34,500	44,944	60,205
Net income	113,988	141,741	132,558
Other comprehensive income (loss):
Foreign currency translation and other	1	263	(98)
Cash flow hedge, net of income taxes	0	0	(15)
Other comprehensive income (loss)	1	263	(113)
Comprehensive income	$ 113,989	$ 142,004	$ 132,445
Net income per common share:
Net income per common share - basic (in dollars per share)	$ 2.44	$ 2.99	$ 2.77
Net income per common share - diluted (in dollars per share)	$ 2.40	$ 2.91	$ 2.68
Weighted average common shares outstanding:
Weighted average common shares outstanding - basic (shares)	46,704	47,371	47,807
Weighted average common shares outstanding - diluted (shares)	47,593	48,668	49,430