CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY Statement - USD ($) $ in Thousands	Total	Common Stock	Common Stock Restricted Stock Units (RSUs)	Common Stock Restricted Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Balance, beginning of period (in shares) at Dec. 31, 2017		52,983,685
Balance, beginning of period at Dec. 31, 2017	$ 974,947	$ 53			$ 473,874	$ 518,820		$ (17,623)
Treasury stock, beginning of period (in shares) at Dec. 31, 2017							19,735
Treasury stock, beginning period at Dec. 31, 2017							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested (in shares)			186,327
Stock units withheld for employee taxes	(6,986)				(6,986)
Stock units withheld for employee taxes (in shares)			(61,950)
Proceeds from stock options exercises	7,649				7,649
Proceeds from stock options exercises (in shares)		198,936
Stock-based compensation expense	11,485				11,485
Foreign currency translation adjustments, net of tax	3,309							3,309
Change in unrealized gains and loss on cash-flow hedges, net of tax	69							69
Cumulative effect of the adoption of ASU | ASU 2014-09	457					457
Net income	64,418					64,418
Balance, end of period (in shares) at Mar. 31, 2018		53,306,998
Balance, end of period at Mar. 31, 2018	1,055,348	$ 53			486,022	583,695		(14,245)
Treasury stock, end of period (in shares) at Mar. 31, 2018							19,735
Treasury stock, end of period at Mar. 31, 2018							$ (177)
Balance, beginning of period (in shares) at Dec. 31, 2017		52,983,685
Balance, beginning of period at Dec. 31, 2017	974,947	$ 53			473,874	518,820		(17,623)
Treasury stock, beginning of period (in shares) at Dec. 31, 2017							19,735
Treasury stock, beginning period at Dec. 31, 2017							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Net income	180,291
Balance, end of period (in shares) at Sep. 30, 2018		53,991,844
Balance, end of period at Sep. 30, 2018	1,195,935	$ 54			530,837	699,568		(34,347)
Treasury stock, end of period (in shares) at Sep. 30, 2018							19,735
Treasury stock, end of period at Sep. 30, 2018							$ (177)
Balance, beginning of period (in shares) at Mar. 31, 2018		53,306,998
Balance, beginning of period at Mar. 31, 2018	1,055,348	$ 53			486,022	583,695		(14,245)
Treasury stock, beginning of period (in shares) at Mar. 31, 2018							19,735
Treasury stock, beginning period at Mar. 31, 2018							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested (in shares)			12,348
Stock units withheld for employee taxes	(224)				(224)
Stock units withheld for employee taxes (in shares)			(1,942)
Proceeds from stock options exercises	14,648	$ 1			14,647
Proceeds from stock options exercises (in shares)		367,863
Stock-based compensation expense	10,686				10,686
Foreign currency translation adjustments, net of tax	(15,834)							(15,834)
Change in unrealized gains and loss on cash-flow hedges, net of tax	(2,076)							(2,076)
Net income	50,255					50,255
Balance, end of period (in shares) at Jun. 30, 2018		53,685,267
Balance, end of period at Jun. 30, 2018	1,112,803	$ 54			511,131	633,950		(32,155)
Treasury stock, end of period (in shares) at Jun. 30, 2018							19,735
Treasury stock, end of period at Jun. 30, 2018							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested (in shares)			12,694
Stock units withheld for employee taxes	(349)				(349)
Stock units withheld for employee taxes (in shares)			(2,683)
Proceeds from stock options exercises	9,561				9,561
Proceeds from stock options exercises (in shares)		296,566
Stock-based compensation expense	10,494				10,494
Foreign currency translation adjustments, net of tax	(2,118)							(2,118)
Change in unrealized gains and loss on cash-flow hedges, net of tax	(74)							(74)
Net income	65,618					65,618
Balance, end of period (in shares) at Sep. 30, 2018		53,991,844
Balance, end of period at Sep. 30, 2018	$ 1,195,935	$ 54			530,837	699,568		(34,347)
Treasury stock, end of period (in shares) at Sep. 30, 2018							19,735
Treasury stock, end of period at Sep. 30, 2018							$ (177)
Balance, beginning of period (in shares) at Dec. 31, 2018	54,080,192	54,080,192
Balance, beginning of period at Dec. 31, 2018	$ 1,262,596	$ 54			544,700	759,533		(41,514)
Treasury stock, beginning of period (in shares) at Dec. 31, 2018							19,735
Treasury stock, beginning period at Dec. 31, 2018							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested (in shares)			242,414
Stock units withheld for employee taxes	(13,483)				(13,483)
Stock units withheld for employee taxes (in shares)			(81,562)
Proceeds from stock options exercises	11,890				11,890
Proceeds from stock options exercises (in shares)		323,464
Stock-based compensation expense	10,425				10,425
Foreign currency translation adjustments, net of tax	2,943							2,943
Change in unrealized gains and loss on cash-flow hedges, net of tax	3,100							3,100
Net income	60,754					60,754
Balance, end of period (in shares) at Mar. 31, 2019		54,564,508
Balance, end of period at Mar. 31, 2019	$ 1,338,225	$ 54			553,532	820,287		(35,471)
Treasury stock, end of period (in shares) at Mar. 31, 2019							19,735
Treasury stock, end of period at Mar. 31, 2019							$ (177)
Balance, beginning of period (in shares) at Dec. 31, 2018	54,080,192	54,080,192
Balance, beginning of period at Dec. 31, 2018	$ 1,262,596	$ 54			544,700	759,533		(41,514)
Treasury stock, beginning of period (in shares) at Dec. 31, 2018							19,735
Treasury stock, beginning period at Dec. 31, 2018							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Net income	$ 186,533
Balance, end of period (in shares) at Sep. 30, 2019	54,949,098	54,949,098
Balance, end of period at Sep. 30, 2019	$ 1,492,117	$ 55			589,764	946,066		(43,591)
Treasury stock, end of period (in shares) at Sep. 30, 2019							19,735
Treasury stock, end of period at Sep. 30, 2019							$ (177)
Balance, beginning of period (in shares) at Mar. 31, 2019		54,564,508
Balance, beginning of period at Mar. 31, 2019	1,338,225	$ 54			553,532	820,287		(35,471)
Treasury stock, beginning of period (in shares) at Mar. 31, 2019							19,735
Treasury stock, beginning period at Mar. 31, 2019							$ (177)
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested (in shares)			11,757
Stock units withheld for employee taxes	(363)				(363)
Stock units withheld for employee taxes (in shares)			(2,084)
Proceeds from stock options exercises	10,584	$ 1			10,583
Proceeds from stock options exercises (in shares)		205,108
Stock-based compensation expense	10,867				10,867
Foreign currency translation adjustments, net of tax	2,620							2,620
Change in unrealized gains and loss on cash-flow hedges, net of tax	1,537							1,537
Net income	58,777					58,777
Balance, end of period (in shares) at Jun. 30, 2019		54,779,289
Balance, end of period at Jun. 30, 2019	1,422,247	$ 55			574,619	879,064		(31,314)
Treasury stock, end of period (in shares) at Jun. 30, 2019							19,735
Treasury stock, end of period at Jun. 30, 2019							$ (177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued in connection with acquisitions				18,787
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested (in shares)			17,216
Stock units withheld for employee taxes	(1,090)				(1,090)
Stock units withheld for employee taxes (in shares)			(5,961)
Proceeds from stock options exercises	6,326				6,326
Proceeds from stock options exercises (in shares)		139,767
Stock-based compensation expense	9,909				9,909
Foreign currency translation adjustments, net of tax	(10,114)							(10,114)
Change in unrealized gains and loss on cash-flow hedges, net of tax	(2,163)							(2,163)
Net income	$ 67,002					67,002
Balance, end of period (in shares) at Sep. 30, 2019	54,949,098	54,949,098
Balance, end of period at Sep. 30, 2019	$ 1,492,117	$ 55			$ 589,764	$ 946,066		$ (43,591)
Treasury stock, end of period (in shares) at Sep. 30, 2019							19,735
Treasury stock, end of period at Sep. 30, 2019							$ (177)