EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	400,000	200,000	400,000	200,000
Basic earnings per share [Abstract]
Net income	$ 44,606	$ 17,191	$ 84,712	$ 43,448
Income attributable to unvested stock-based compensation awards	(188)	(83)	(353)	(219)
Income available to common shareholders	$ 44,418	$ 17,108	$ 84,359	$ 43,229
Weighted-average common shares outstanding - basic (in shares)	51,140,000	48,525,000	51,037,000	46,913,000
Basic earnings per share (in dollars per share)	$ 0.87	$ 0.35	$ 1.65	$ 0.92
Diluted earnings per share [Abstract]
Net income	$ 44,606	$ 17,191	$ 84,712	$ 43,448
Income attributable to unvested stock-based compensation awards	(188)	(83)	(353)	(219)
Income available to common shareholders	$ 44,418	$ 17,108	$ 84,359	$ 43,229
Weighted-average common shares outstanding - basic (in shares)	51,140,000	48,525,000	51,037,000	46,913,000
Assumed exercise of stock options (in shares)	583,000	626,000	576,000	665,000
Weighted-average common shares outstanding - diluted (in shares)	51,723,000	49,151,000	51,613,000	47,578,000
Diluted earnings per share (in dollars per share)	$ 0.86	$ 0.35	$ 1.63	$ 0.91
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