EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic earnings per share:
NET INCOME		$ 14,165	$ 11,513	$ 34,273	$ 26,446
Weighted-average common shares		28,972,000	28,855,000	28,834,000	29,175,000
Basic earnings per share		$ 0.49	$ 0.40	$ 1.19	$ 0.91
Diluted earnings per share:
NET INCOME		$ 14,165	$ 11,513	$ 34,273	$ 26,446
Weighted-average common shares		28,972,000	28,855,000	28,834,000	29,175,000
Effect of dilutive awards:
Employee stock plans		653,000	443,000	646,000	681,000
Diluted weighted-average common shares		29,625,000	29,298,000	29,480,000	29,856,000
Diluted earnings per share	[1]	$ 0.48	$ 0.39	$ 1.16	$ 0.89
Stock awards excluded in the computation of diluted earnings per share		0	69,000	0	8,000

[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 outstanding performance-based awards in the 2016 and 2015 calculations as the shares were not contingently issuable as of the end of the reporting periods.