Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($)
shares in Thousands, $ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Statement of Comprehensive Income [Abstract]        
Revenue $ 472,636 $ 382,859 $ 1,414,367 $ 1,060,513
Cost of revenue 318,169 256,850 953,249 722,954
Gross profit 154,467 126,009 461,118 337,559
Operating expenses:        
Selling, general and administrative 99,995 83,098 297,359 229,377
Depreciation and amortization 7,789 5,304 21,888 15,631
Total operating expenses 107,784 88,402 319,247 245,008
Income from operations 46,683 37,607 141,871 92,551
Interest expense, net, and other 3,016 2,013 9,065 5,797
Income before income taxes 43,667 35,594 132,806 86,754
Income tax expense 16,371 1,947 53,319 25,028
Net income 27,296 33,647 79,487 61,726
Other comprehensive income (loss):        
Foreign currency translation and other 40 54 165 42
Unrealized gain (loss) on cash flow hedge, net of income taxes 231 (367) (343) (331)
Other comprehensive income (loss) 271 (313) (178) (289)
Comprehensive income $ 27,567 $ 33,334 $ 79,309 $ 61,437
Net income per common share:        
Basic (in dollars per share) $ 0.57 $ 0.71 $ 1.66 $ 1.30
Diluted (in dollars per share) $ 0.55 $ 0.69 $ 1.61 $ 1.27
Weighted average common shares outstanding:        
Basic (shares) 48,049 47,674 47,993 47,466
Diluted (shares) 49,410 48,978 49,287 48,737