Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2008	$ 147,298	$ 17,411	$ (64)	$ 164,645
Balance (in Shares) at Dec. 31, 2008	33,646,821
Components of comprehensive income:
Net income		19,674		19,674
Impairment of Auction Rate Securities valuation reserve adj.			340	340
Unrealized (Gains) Losses			(109)	(109)
Foreign exchange gain			187	187
Total comprehensive income				20,092
Exercise of stock options	11,824			11,824
Exercise of stock options (in Shares)	1,217,272
Shares purchased through ESPP	1,794			1,794
Shares purchased through ESPP (in Shares)	161,026
Stock-based compensation expense, net of forfeitures	14,484			14,484
Compensation expense for non-employee stock options	118			118
Release of restricted stock upon vesting (in Shares)	140,197
Balance at Dec. 31, 2009	175,518	37,085	354	212,957
Balance (in Shares) at Dec. 31, 2009	35,165,316
Components of comprehensive income:
Net income		29,563		29,563
Impairment of Auction Rate Securities valuation reserve adj.			160	160
Unrealized (Gains) Losses			104	104
Foreign exchange gain			1,361	1,361
Total comprehensive income				31,188
Exercise of stock options	15,597			15,597
Exercise of stock options (in Shares)	1,452,245
Repurchase of common shares	(31,527)			(31,527)
Repurchase of common shares (in Shares)	(1,899,789)
Shares purchased through ESPP	1,885			1,885
Shares purchased through ESPP (in Shares)	114,387
Stock-based compensation expense, net of forfeitures	16,803			16,803
Compensation expense for non-employee stock options	(7)			(7)
Release of restricted stock upon vesting (in Shares)	230,874
Balance at Dec. 31, 2010	178,269	66,647	1,979	246,895
Balance (in Shares) at Dec. 31, 2010	35,063,033			35,063,033
Components of comprehensive income:
Net income		13,301		13,301
Impairment of Auction Rate Securities valuation reserve adj.			270	270
Unrealized (Gains) Losses			(37)	(37)
Foreign exchange gain			1,381	1,381
Total comprehensive income				14,915
Exercise of stock options	4,630			4,630
Exercise of stock options (in Shares)	685,417
Repurchase of common shares	(38,472)			(38,472)
Repurchase of common shares (in Shares)	(2,485,500)
Shares purchased through ESPP	1,773			1,773
Shares purchased through ESPP (in Shares)	149,981
Stock-based compensation expense, net of forfeitures	13,123			13,123
Compensation expense for non-employee stock options	13			13
Release of restricted stock upon vesting (in Shares)	413,101
Balance at Dec. 31, 2011	$ 159,336	$ 79,948	$ 3,593	$ 242,877
Balance (in Shares) at Dec. 31, 2011	33,826,032			33,826,032