EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Basic earnings per share:
Net income	$ 6,326	$ 7,512	$ 10,599	$ 9,854	$ 8,929	$ 12,634	$ 15,587	$ 12,314	$ 34,291		$ 49,464		$ 23,269
Weighted Average Common Shares	28,077,000	28,799,000	28,938,000	28,628,000	28,134,000	27,894,000	27,844,000	27,470,000	28,609,000		27,837,000		26,920,000
Basic earnings per share	$ 0.23	$ 0.26	$ 0.37	$ 0.34	$ 0.32	$ 0.45	$ 0.56	$ 0.45	$ 1.2		$ 1.78		$ 0.86
Diluted earnings per share:
Net income	$ 6,326	$ 7,512	$ 10,599	$ 9,854	$ 8,929	$ 12,634	$ 15,587	$ 12,314	$ 34,291		$ 49,464		$ 23,269
Weighted Average Common Shares	28,077,000	28,799,000	28,938,000	28,628,000	28,134,000	27,894,000	27,844,000	27,470,000	28,609,000		27,837,000		26,920,000
Effect of dilutive securities:
Employee stock plans									1,355,000	[1]	1,719,000	[1]	1,377,000	[1]
Diluted weighted average common shares	29,171,000	29,879,000	30,346,000	30,187,000	29,844,000	29,283,000	29,535,000	29,358,000	29,964,000	[1]	29,556,000	[1]	28,297,000	[1]
Diluted earnings per share	$ 0.22	$ 0.25	$ 0.35	$ 0.33	$ 0.30	$ 0.43	$ 0.53	$ 0.42	$ 1.14	[1]	$ 1.67	[1]	$ 0.82	[1]
Antidilutive shares attributable to stock-based awards outstanding excluded from computation of diluted earnings per share									294,965		159,316		2,788,913

[1] The Company includes the shares underlying performance-based awards in the calculation of diluted earnings per share when they become contingently issuable per ASC 260-10, Earnings per Share and excludes such shares when they are not contingently issuable. The Company has excluded all performance-based awards underlying the 2011 awards in the 2011 calculation as those shares were not contingently issuable as of the end of the period, and has included all performance-based awards underlying the 2010 and 2009 awards in the 2010 and 2009 calculation, respectively, as those shares were contingently issuable upon the satisfaction of the annual targets consisting of net revenue and non-GAAP operating earnings as of the end of the period.