EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	400,000	200,000	400,000	100,000
Basic earnings per share [Abstract]
Net income	$ 43,106	$ 35,243	$ 127,818	$ 78,691
Income attributable to unvested stock-based compensation awards	(191)	(164)	(563)	(387)
Income available to common shareholders	$ 42,915	$ 35,079	$ 127,255	$ 78,304
Weighted-average common shares outstanding - basic (in shares)	51,250,000	50,703,000	51,108,000	48,189,000
Basic earnings per share (in dollars per share)	$ 0.84	$ 0.69	$ 2.49	$ 1.62
Diluted earnings per share [Abstract]
Net income	$ 43,106	$ 35,243	$ 127,818	$ 78,691
Income attributable to unvested stock-based compensation awards	(191)	(164)	(563)	(387)
Income available to common shareholders	$ 42,915	$ 35,079	$ 127,255	$ 78,304
Weighted-average common shares outstanding - basic (in shares)	51,250,000	50,703,000	51,108,000	48,189,000
Assumed exercise of stock options (in shares)	608,000	585,000	590,000	640,000
Weighted-average common shares outstanding - diluted (in shares)	51,858,000	51,288,000	51,698,000	48,829,000
Diluted earnings per share (in dollars per share)	$ 0.83	$ 0.68	$ 2.46	$ 1.60
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)					2,500,000
Number of common shares repurchased (in shares)			0