CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Common Stock 2012 Directors Plan	Common Stock Restricted Stock Units (RSUs)	Additional Paid-in Capital	Additional Paid-in Capital Restricted Stock Units (RSUs)	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive (Loss)/ Income
Balance, beginning of period at Dec. 31, 2015	$ 613,223	$ 49			$ 303,363		$ 345,054		$ (35,150)
Balance, beginning of period (in shares) at Dec. 31, 2015		50,166,537
Treasury stock, beginning of period at Dec. 31, 2015								$ (93)
Treasury stock, beginning of period (in shares) at Dec. 31, 2015								10,507
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Forfeiture of stock issued in connection with acquisition					84			$ (84)
Forfeiture of stock issued in connection with acquisition (in shares)		9,228						(9,228)
Stock-based compensation expense	46,100				46,100
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures [Abstract]
Stock issued (in shares)			6,510
Stock units vested, net of shares withheld for employee taxes (in shares)				38,064
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested, net of shares withheld for employee taxes	2,069					$ 2,069
Proceeds from stock option exercises	18,028	$ 1			18,027
Proceeds from stock options exercises (in shares)		895,804
Excess tax benefits	5,264				5,264
Foreign currency translation adjustments	(2,538)								(2,538)
Foreign currency translation adjustments, net of tax	(2,538)
Change in unrealized gains and losses on cash flow hedges, net of tax	0
Net income	99,266						99,266
Balance, end of period at Dec. 31, 2016	781,412	$ 50			374,907		444,320		(37,688)
Balance, end of period (in shares) at Dec. 31, 2016		51,097,687
Treasury stock, end of period at Dec. 31, 2016								$ (177)
Treasury stock, end of period (in shares) at Dec. 31, 2016								19,735
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	48,173				48,173
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures [Abstract]
Stock units vested (in shares)				140,043
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units withheld for employee taxes	(3,300)				(3,300)
Stock units withheld for employee taxes (in shares)				(43,479)
Proceeds from stock option exercises	54,097	$ 3			54,094
Proceeds from stock options exercises (in shares)		1,789,434
Foreign currency translation adjustments	20,065								20,065
Foreign currency translation adjustments, net of tax	20,065
Change in unrealized gains and losses on cash flow hedges, net of tax	0
Cumulative effect of the adoption of ASU	1,740
Cumulative effect of the adoption of ASU | ASU 2016-09							1,740
Net income	72,760						72,760
Balance, end of period at Dec. 31, 2017	$ 974,947	$ 53			473,874		518,820		(17,623)
Balance, end of period (in shares) at Dec. 31, 2017	52,983,685	52,983,685
Treasury stock, end of period at Dec. 31, 2017								$ (177)
Treasury stock, end of period (in shares) at Dec. 31, 2017								19,735
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	$ 44,279				44,279
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures [Abstract]
Stock units vested (in shares)				222,675
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units withheld for employee taxes	(8,131)				(8,131)
Stock units withheld for employee taxes (in shares)				(71,334)
Proceeds from stock option exercises	34,679	$ 1			34,678
Proceeds from stock options exercises (in shares)		945,166
Foreign currency translation adjustments, net of tax	(21,338)								(21,338)
Change in unrealized gains and losses on cash flow hedges, net of tax	(2,553)								(2,553)
Cumulative effect of the adoption of ASU	457
Cumulative effect of the adoption of ASU | ASU 2014-09	457
Net income	240,256						240,256
Balance, end of period at Dec. 31, 2018	$ 1,262,596	$ 54			$ 544,700		$ 759,533		$ (41,514)
Balance, end of period (in shares) at Dec. 31, 2018	54,080,192	54,080,192
Treasury stock, end of period at Dec. 31, 2018								$ (177)
Treasury stock, end of period (in shares) at Dec. 31, 2018								19,735