EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	500	400	200
Basic earnings per share [Abstract]
Net income	$ 169,063	$ 168,641	$ 150,717
Income attributable to unvested stock-based compensation awards	(400)	(744)	(597)
Income available to common shareholders	$ 168,663	$ 167,897	$ 150,120
Weighted-average common shares outstanding - basic (in shares)	51,732	51,165	48,843
Basic earnings per share (in dollars per share)	$ 3.26	$ 3.28	$ 3.07
Diluted earnings per share [Abstract]
Net income	$ 169,063	$ 168,641	$ 150,717
Income attributable to unvested stock-based compensation awards	(400)	(744)	(597)
Income available to common shareholders	$ 168,663	$ 167,897	$ 150,120
Weighted-average common shares outstanding (in shares)	51,732	51,165	48,843
Assumed exercise of stock options (in shares)	516	583	627
Weighted-average common shares outstanding - diluted (in shares)	52,248	51,748	49,470
Diluted earnings per share (in dollars per share)	$ 3.23	$ 3.24	$ 3.03
Cash dividends declared per share (in dollars per share)	$ 1.58	$ 1.44	$ 1.32
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)	2,500	2,600
Number of common shares repurchased (in shares)	0	0