EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	300,000	600,000	500,000	500,000
Basic earnings per share [Abstract]
Net income	$ 21,989	$ 18,367	$ 63,352	$ 58,264
Income attributable to unvested stock-based compensation awards	(121)	(125)	(315)	(372)
Income available to common shareholders	21,868	18,242	63,037	57,892
Weighted-average common shares outstanding - basic (in shares)	40,121,000	39,384,000	39,914,000	39,095,000
Basic earnings per share (in dollars per share)	$ 0.55	$ 0.46	$ 1.58	$ 1.48
Diluted earnings per share [Abstract]
Net income	21,989	18,367	63,352	58,264
Income attributable to unvested stock-based compensation awards	(121)	(125)	(315)	(372)
Income available to common shareholders	$ 21,868	$ 18,242	$ 63,037	$ 57,892
Weighted-average common shares outstanding (in shares)	40,121,000	39,384,000	39,914,000	39,095,000
Assumed exercise of stock options (in shares)	506,000	486,000	474,000	496,000
Weighted-average shares - diluted (in shares)	40,627,000	39,870,000	40,388,000	39,591,000
Diluted earnings per share (in dollars per share)	$ 0.54	$ 0.46	$ 1.56	$ 1.46
Cash dividends declared per share (in dollars per share)	$ 0.28	$ 0.27	$ 0.82	$ 0.79
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)					2,000,000
Number of common shares repurchased (in shares)			24,000