EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)	500,000	300,000
Basic earnings per share [Abstract]
Net income	$ 20,241	$ 18,826
Income attributable to unvested stock-based compensation awards	(79)	(104)
Income available to common shareholders	20,162	18,722
Weighted-average common shares outstanding - basic (in shares)	39,703,000	38,573,000
Basic earnings per share (in dollars per share)	$ 0.51	$ 0.49
Diluted earnings per share [Abstract]
Net income	20,241	18,826
Income attributable to unvested stock-based compensation awards	(79)	(104)
Income available to common shareholders	$ 20,162	$ 18,722
Weighted-average common shares outstanding (in shares)	39,703,000	38,573,000
Assumed exercise of stock options (in shares)	463,000	535,000
Weighted-average shares - diluted (in shares)	40,166,000	39,108,000
Diluted earnings per share (in dollars per share)	$ 0.50	$ 0.48
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)	2,000,000
Number of common shares repurchased (in shares)	22,000