EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	300	200	300
Basic earnings per share [Abstract]
Net income	$ 91,230	$ 91,353	$ 78,829
Income attributable to unvested stock-based compensation awards	(453)	(456)	(433)
Income available to common shareholders	$ 90,777	$ 90,897	$ 78,396
Weighted-average common shares outstanding - basic (in shares)	40,996	40,548	40,000
Basic earnings per share (in dollars per share)	$ 2.21	$ 2.24	$ 1.96
Diluted earnings per share [Abstract]
Net income	$ 91,230	$ 91,353	$ 78,829
Income attributable to unvested stock-based compensation awards	(453)	(456)	(433)
Income available to common shareholders	$ 90,777	$ 90,897	$ 78,396
Weighted-average common shares outstanding (in shares)	40,996	40,548	40,000
Assumed exercise of stock options (in shares)	405	481	504
Weighted-average common shares outstanding - diluted (in shares)	41,401	41,029	40,504
Diluted earnings per share (in dollars per share)	$ 2.19	$ 2.22	$ 1.94
Cash dividends declared per share (in dollars per share)	$ 1.22	$ 1.16	$ 1.10
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)	2,200	2,000
Number of common shares repurchased (in shares)	300	100	0