Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Treasury stock	Accumulated Other comprehensive income (loss)	Retained earnings
Cumulative effect adjustment upon adoption	$ 2,839		$ 2,743			$ 96
Balance at Dec. 31, 2015	822,902	$ 518	657,354	$ (190,439)	$ (17,375)	372,844
Balance, shares common stock at Dec. 31, 2015		51,808,000
Balance, shares treasury stock at Dec. 31, 2015				(4,476,000)
Comprehensive income (loss), net of tax	37,749				(7,200)	44,949
Exercise of common stock options	$ 1,345	$ 1	1,344
Exercise of common stock options, shares	115,000	116,000
Restricted stock vested	$ 0	$ 8	(8)
Restricted stock vested (in shares)		787,000
Common stock issued in connection with business acquisition	(73)		(73)
Common stock issued in connection with business acquisitions, shares		30,000
Stock-based compensation	31,726		31,726
Non-cash settlement of employee-related liabilities by issuing RSUs	3,059		3,059
Stock repurchases	(83,291)			$ (83,291)
Stock repurchases, shares				(1,981,000)
Stock issued pursuant to ESPP	9,759	$ 3	9,756
Stock issued pursuant to ESPP, shares		297,000
Balance at Dec. 31, 2016	826,015	$ 530	705,901	$ (273,730)	(24,575)	417,889
Balance, shares treasury stock at Dec. 31, 2016				(6,457,000)
Balance, shares common stock at Dec. 31, 2016		53,038,000
Comprehensive income (loss), net of tax	17,368				32,713	(15,345)
Exercise of common stock options	$ 2,066	$ 2	2,064
Exercise of common stock options, shares	165,000	166,000
Restricted stock vested	$ 0	$ 7	(7)
Restricted stock vested (in shares)		761,000
Common stock issued in connection with business acquisition	0
Stock-based compensation	26,532		26,532
Non-cash settlement of employee-related liabilities by issuing RSUs	1,166		1,166
Stock repurchases	$ (101,844)			$ (101,844)
Stock repurchases, shares	(2,363,988)			(2,613,000)
Stock issued pursuant to ESPP	$ 10,008	$ 3	10,005
Stock issued pursuant to ESPP, shares	300,000	284,000
Balance at Dec. 31, 2017	$ 781,311	$ 542	745,661	$ (375,574)	8,138	402,544
Balance, shares treasury stock at Dec. 31, 2017	(9,070,000)			(9,070,000)
Balance, shares common stock at Dec. 31, 2017		54,249,000
Cumulative effect adjustment upon adoption	$ 4,674					4,674
Comprehensive income (loss), net of tax	(21,923)				(20,952)	(971)
Exercise of common stock options	$ 1,071	$ 1	1,070
Exercise of common stock options, shares	75,000	75,000
Restricted stock vested	$ 0	$ 6	(6)
Restricted stock vested (in shares)		639,000
Common stock issued in connection with business acquisition	123		123
Common stock issued in connection with business acquisitions, shares		5,000
Escrow settlement in connection with business acquisition	(945)
Equity component of convertible senior notes issued	20,573		20,573
Stock-based compensation	45,281		45,281
Stock repurchases	$ (113,509)			$ (113,509)
Stock repurchases, shares	(3,726,042)			(3,857,000)
Stock issued pursuant to ESPP	$ 9,452	$ 4	9,448
Stock issued pursuant to ESPP, shares	400,000	379,000
Balance at Dec. 31, 2018	$ 726,108	$ 553	$ 821,205	$ (489,083)	$ (12,814)	$ 406,247
Balance, shares treasury stock at Dec. 31, 2018	(12,927,000)			(12,927,000)
Balance, shares common stock at Dec. 31, 2018		55,347,000