EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Basic earnings per share:
Net income	$ 16,111		$ 16,654		$ 45,190		$ 41,229
Weighted-average common shares (in Shares)	30,013,000		29,762,000		30,186,000		29,235,000
Basic earnings per share (in dollars per share)	$ 0.54		$ 0.56		$ 1.50		$ 1.41
Diluted earnings per share:
Net income	$ 16,111		$ 16,654		$ 45,190		$ 41,229
Weighted-average common shares (in Shares)	30,013,000		29,762,000		30,186,000		29,235,000
Effect of dilutive securities:
Employee stock plans (shares)	744,000	[1]	890,000	[1]	867,000	[1]	1,002,000	[1]
Diluted weighted-average common shares (in Shares)	30,757,000	[1]	30,652,000	[1]	31,053,000	[1]	30,237,000	[1]
Diluted earnings per share (in dollars per share)	$ 0.52	[1]	$ 0.54	[1]	$ 1.46	[1]	$ 1.36	[1]
Antidilutive shares attributable to stock-based awards outstanding excluded from computation of diluted earnings per share (in Shares)			35,000				149,000

[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 2014 and 2013 awards in the 2014 and 2013 calculations, respectively, as those shares were not contingently issuable as of the end of the period.