EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	0	600,000	300,000	500,000
Basic earnings per share [Abstract]
Net income	$ 27,160	$ 25,022	$ 77,420	$ 71,159
Income attributable to unvested stock-based compensation awards	(157)	(129)	(398)	(352)
Income available to common shareholders	$ 27,003	$ 24,893	$ 77,022	$ 70,807
Weighted-average common shares outstanding - basic (in shares)	44,184,000	40,873,000	44,023,000	40,741,000
Basic earnings per share (in dollars per share)	$ 0.61	$ 0.61	$ 1.75	$ 1.74
Diluted earnings per share [Abstract]
Net income	$ 27,160	$ 25,022	$ 77,420	$ 71,159
Income attributable to unvested stock-based compensation awards	(157)	(129)	(398)	(352)
Income available to common shareholders	$ 27,003	$ 24,893	$ 77,022	$ 70,807
Weighted-average common shares outstanding - basic (in shares)	44,184,000	40,873,000	44,023,000	40,741,000
Assumed exercise of stock options (in shares)	394,000	386,000	359,000	400,000
Weighted-average common shares outstanding - diluted (in shares)	44,578,000	41,259,000	44,382,000	41,141,000
Diluted earnings per share (in dollars per share)	$ 0.61	$ 0.60	$ 1.74	$ 1.72
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)					2,200,000
Number of common shares repurchased (in shares)			0		265,230