Consolidated Statements of Stockholders' Equity Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Cumulative Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balance,shares at Dec. 31, 2012		38,342
Balance at Dec. 31, 2012	$ 754,611	$ 38	$ 394,427	$ 4	$ 360,142
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains and losses on available-for-sale Securities, Net of Tax	(24)			(24)
Change in unrealized gains and losses on derivatives, Net of Tax	89			89
Net Income	55,217				55,217
Share-based Compensation expense	17,419		17,419
Stock Repurchased and Retired During Period, Shares		(2,018)
Stock Repurchased and Retired During Period, Value	(63,584)	$ (1)			(63,583)
Issuance of common stock under stock-based compensation plans, shares		516
Issuance of common stock under stock-based compensation plans	9,626	$ 0	9,626
Income tax impact associated with stock option exercises	429		429
Balance,shares at Dec. 31, 2013		36,840
Balance at Dec. 31, 2013	773,783	$ 37	421,901	69	351,776
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains and losses on available-for-sale Securities, Net of Tax	(9)			(9)
Change in unrealized gains and losses on derivatives, Net of Tax	(22)			(22)
Net Income	8,788				8,788
Share-based Compensation expense	19,983		19,983
Stock Repurchased and Retired During Period, Shares		(2,908)
Stock Repurchased and Retired During Period, Value	(93,218)	$ (2)			(93,216)
Issuance of common stock under stock-based compensation plans, shares		777
Issuance of common stock under stock-based compensation plans	12,741	$ 0	12,741
Income tax impact associated with stock option exercises	(481)		(481)
Balance,shares at Dec. 31, 2014		34,709
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)
Change in unrealized gains and losses on derivatives, Net of Tax	0			0
Net Income	48,584				48,584
Share-based Compensation expense	16,813		16,813
Stock Repurchased and Retired During Period, Shares		(3,855)
Stock Repurchased and Retired During Period, Value	(120,309)	$ (4)			(120,305)
Issuance of common stock under stock-based compensation plans, shares		1,747
Issuance of common stock under stock-based compensation plans	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
Balance at Dec. 31, 2015	$ 708,710	$ 33	$ 513,047	$ 3	$ 195,627