EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	600,000	300,000	500,000	200,000
Basic earnings per share [Abstract]
Net income	$ 25,022	$ 22,371	$ 71,159	$ 68,220
Income attributable to unvested stock-based compensation awards	(129)	(115)	(352)	(337)
Income available to common shareholders	$ 24,893	$ 22,256	$ 70,807	$ 67,883
Weighted-average common shares outstanding - basic (in shares)	40,873,000	40,596,000	40,741,000	40,543,000
Basic earnings per share (in dollars per share)	$ 0.61	$ 0.55	$ 1.74	$ 1.67
Diluted earnings per share [Abstract]
Net income	$ 25,022	$ 22,371	$ 71,159	$ 68,220
Income attributable to unvested stock-based compensation awards	(129)	(115)	(352)	(337)
Income available to common shareholders	$ 24,893	$ 22,256	$ 70,807	$ 67,883
Weighted-average common shares outstanding - basic (in shares)	40,873,000	40,596,000	40,741,000	40,543,000
Assumed exercise of stock options (in shares)	386,000	453,000	400,000	482,000
Weighted-average common shares outstanding - diluted (in shares)	41,259,000	41,049,000	41,141,000	41,025,000
Diluted earnings per share (in dollars per share)	$ 0.60	$ 0.54	$ 1.72	$ 1.65
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)					2,000,000
Number of common shares repurchased (in shares)			265,230		123,000