EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	600,000	300,000	400,000	200,000
Basic earnings per share [Abstract]
Net income	$ 23,840	$ 23,676	$ 46,137	$ 45,850
Income attributable to unvested stock-based compensation awards	(99)	(123)	(177)	(221)
Income available to common shareholders	$ 23,741	$ 23,553	$ 45,960	$ 45,629
Weighted-average common shares outstanding - basic (in shares)	40,690,000	40,574,000	40,674,000	40,517,000
Basic earnings per share (in dollars per share)	$ 0.58	$ 0.58	$ 1.13	$ 1.13
Diluted earnings per share [Abstract]
Net income	$ 23,840	$ 23,676	$ 46,137	$ 45,850
Income attributable to unvested stock-based compensation awards	(99)	(123)	(177)	(221)
Income available to common shareholders	$ 23,741	$ 23,553	$ 45,960	$ 45,629
Weighted-average common shares outstanding - basic (in shares)	40,690,000	40,574,000	40,674,000	40,517,000
Assumed exercise of stock options (in shares)	404,000	484,000	405,000	497,000
Weighted-average common shares outstanding - diluted (in shares)	41,094,000	41,058,000	41,079,000	41,014,000
Diluted earnings per share (in dollars per share)	$ 0.58	$ 0.57	$ 1.12	$ 1.11
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