EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 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	$ 39,218	$ 43,106	$ 126,179	$ 127,818
Income attributable to unvested stock-based compensation awards	(102)	(191)	(331)	(563)
Income available to common shareholders	$ 39,116	$ 42,915	$ 125,848	$ 127,255
Weighted-average common shares outstanding - basic (in shares)	51,750,000	51,250,000	51,644,000	51,108,000
Basic earnings per share (in dollars per share)	$ 0.76	$ 0.84	$ 2.44	$ 2.49
Diluted earnings per share [Abstract]
Net income	$ 39,218	$ 43,106	$ 126,179	$ 127,818
Income attributable to unvested stock-based compensation awards	(102)	(191)	(331)	(563)
Income available to common shareholders	$ 39,116	$ 42,915	$ 125,848	$ 127,255
Weighted-average common shares outstanding - basic (in shares)	51,750,000	51,250,000	51,644,000	51,108,000
Assumed exercise of stock options (in shares)	496,000	608,000	522,000	590,000
Weighted-average common shares outstanding - diluted (in shares)	52,246,000	51,858,000	52,166,000	51,698,000
Diluted earnings per share (in dollars per share)	$ 0.75	$ 0.83	$ 2.41	$ 2.46
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