EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Basic earnings per share:
Net income	$ 10,903		$ 7,461
Weighted-average common shares	28,754,000		28,227,000
Basic earnings per share	$ 0.38		$ 0.26
Diluted earnings per share:
Net income	$ 10,903		$ 7,461
Weighted-average common shares	28,754,000		28,227,000
Effect of dilutive securities:
Employee stock plans	1,029,000	[1]	1,208,000	[1]
Diluted weighted-average common shares	29,783,000	[1]	29,435,000	[1]
Diluted earnings per share	$ 0.37	[1]	$ 0.25	[1]
Antidilutive shares attributable to stock-based awards outstanding excluded from computation of diluted earnings per share	281,973		297,531

[1] The Company includes the shares underlying performance-based awards in the calculation of diluted earnings per share if the performance conditions have been satisfied as of the end of the reporting period and excludes such shares when the necessary conditions have not been met. The Company has excluded the shares underlying the 2013 and 2012 awards in the 2013 and 2012 calculation, respectively, as those shares were not contingently issuable as of the end of the period.