EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	500,000	400,000	500,000	400,000
Basic earnings per share [Abstract]
Net income	$ 45,015	$ 44,606	$ 86,961	$ 84,712
Income attributable to unvested stock-based compensation awards	(146)	(188)	(255)	(353)
Income available to common shareholders	$ 44,869	$ 44,418	$ 86,706	$ 84,359
Weighted-average common shares outstanding - basic (in shares)	51,659,000	51,140,000	51,590,000	51,037,000
Basic earnings per share (in dollars per share)	$ 0.87	$ 0.87	$ 1.68	$ 1.65
Diluted earnings per share [Abstract]
Net income	$ 45,015	$ 44,606	$ 86,961	$ 84,712
Income attributable to unvested stock-based compensation awards	(146)	(188)	(255)	(353)
Income available to common shareholders	$ 44,869	$ 44,418	$ 86,706	$ 84,359
Weighted-average common shares outstanding - basic (in shares)	51,659,000	51,140,000	51,590,000	51,037,000
Assumed exercise of stock options (in shares)	529,000	583,000	535,000	576,000
Weighted-average common shares outstanding - diluted (in shares)	52,188,000	51,723,000	52,125,000	51,613,000
Diluted earnings per share (in dollars per share)	$ 0.86	$ 0.86	$ 1.66	$ 1.63
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)					2,500,000	2,500,000
Number of common shares repurchased (in shares)			0	0