CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Employee Stock Options and Awards [Member]	Employee Stock Purchases [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Employee Stock Options and Awards [Member]	Additional Paid-In Capital [Member] Employee Stock Purchases [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2008	$ 259,681			$ 28	$ 145,544			$ (57)	$ 114,166
Beginning Balance (in shares) at Dec. 31, 2008				27,530
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				933
Issuance of common stock under employee stock option and stock award plans	16,723				16,723
Repurchase of common stock (in shares)				(1,403)
Repurchase of common stock	(28,674)			(1)	(28,673)
Issuance of common stock under employee stock purchase plan (in shares)				218
Issuance of common stock under employee stock purchase plan	3,630				3,630
Income tax benefits from employee stock option exercises	1,551				1,551
Stock-based compensation expense		9,148	2,098			9,148	2,098
Payment of dividends to stockholders	(2,695)								(2,695)
Translation adjustment	61							61
Net income	23,269								23,269
Ending Balance at Dec. 31, 2009	284,792			27	150,021			4	134,740
Ending Balance (in shares) at Dec. 31, 2009				27,278
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				1,270
Issuance of common stock under employee stock option and stock award plans	22,862			1	22,861
Net issuance of performance stock unit awards (in shares)				95
Net issuance of performance stock unit awards	(769)				(769)
Repurchase of common stock (in shares)				(396)
Repurchase of common stock	(13,960)				(13,960)
Issuance of common stock under employee stock purchase plan (in shares)				128
Issuance of common stock under employee stock purchase plan	3,402				3,402
Income tax benefits from employee stock option exercises	5,615				5,615
Section 162(m) adjustment for IRS settlement	(2,724)				(2,724)
Stock-based compensation expense		9,726	1,123			9,726	1,123
Payment of dividends to stockholders	(5,577)								(5,577)
Translation adjustment	81							81
Net income	49,464								49,464
Ending Balance at Dec. 31, 2010	354,035			28	175,295			85	178,627
Ending Balance (in shares) at Dec. 31, 2010				28,375
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				1,011
Issuance of common stock under employee stock option and stock award plans	18,464			1	18,463
Net issuance of performance stock unit awards (in shares)				85
Net issuance of performance stock unit awards	0
Repurchase of common stock (in shares)				(1,531)
Repurchase of common stock	(50,000)			(1)	(49,999)
Issuance of common stock under employee stock purchase plan (in shares)				125
Issuance of common stock under employee stock purchase plan	3,747				3,747
Income tax benefits from employee stock option exercises	2,201				2,201
Stock-based compensation expense		7,778	1,161			7,778	1,161
Payment of dividends to stockholders	(5,722)								(5,722)
Translation adjustment	(35)							(35)
Net income	34,291								34,291
Ending Balance at Dec. 31, 2011	$ 365,920			$ 28	$ 158,646			$ 50	$ 207,196
Ending Balance (in shares) at Dec. 31, 2011				28,065