Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balance,shares at Dec. 31, 2014		34,709,000
Balance at Dec. 31, 2014	$ 721,565	$ 35	$ 454,144	$ 38	$ 267,348
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains and losses on available-for-sale securities, net of tax	(35)			(35)
Net Income	48,584				48,584
Share-based Compensation expense	$ 16,813		16,813
Repurchases of common stock, shares	(3,800,000)	(3,770,000)
Repurchases of common stock, value	$ (117,680)	$ (4)			(117,676)
Restricted stock unit withholdings, shares	(85,000)	(85,000)
Restricted stock unit withholdings, value	$ (2,629)				(2,629)
Issuance of common stock under stock-based compensation plans, shares		1,747,000
Issuance of common stock under stock-based compensation plans, value	44,325	$ 2	44,323
Income tax impact associated with stock option exercises	(2,233)		(2,233)
Balance,shares at Dec. 31, 2015		32,601,000
Balance at Dec. 31, 2015	708,710	$ 33	513,047	3	195,627
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains and losses on available-for-sale securities, net of tax	21			21
Change in unrealized gains and losses on derivatives, net of tax	1,914			1,914
Net Income	75,851				75,851
Share-based Compensation expense	$ 19,180		19,180
Repurchases of common stock, shares	(900,000)	(894,000)
Repurchases of common stock, value	$ (38,252)	$ (1)			(38,251)
Restricted stock unit withholdings, shares	(105,000)	(105,000)
Restricted stock unit withholdings, value	$ (4,686)				(4,686)
Issuance of common stock under stock-based compensation plans, shares		1,356,000
Issuance of common stock under stock-based compensation plans, value	31,627	$ 1	31,626
Income tax impact associated with stock option exercises	2,454		2,454
Balance,shares at Dec. 31, 2016		32,958,000
Balance at Dec. 31, 2016	796,819	$ 33	566,307	1,938	228,541
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	92		327		(235)
Change in unrealized gains and losses on available-for-sale securities, net of tax	(73)			(73)
Change in unrealized gains and losses on derivatives, net of tax	(2,716)			(2,716)
Net Income	19,436				19,436
Share-based Compensation expense	$ 22,147		22,147
Repurchases of common stock, shares	(2,400,000)	(2,378,000)
Repurchases of common stock, value	$ (113,161)	$ (2)			(113,159)
Restricted stock unit withholdings, shares	(135,000)	(135,000)
Restricted stock unit withholdings, value	$ (6,415)				(6,415)
Issuance of common stock under stock-based compensation plans, shares		875,000
Issuance of common stock under stock-based compensation plans, value	14,356	$ 0	14,356
Income tax impact associated with stock option exercises	0
Balance,shares at Dec. 31, 2017		31,320,000
Balance at Dec. 31, 2017	$ 730,485	$ 31	$ 603,137	$ (851)	$ 128,168