EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jul. 22, 2009
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)			400,000	200,000
Earnings per Share, Basic [Abstract]
Net income	$ 21,071	$ 17,986	$ 39,897	$ 34,146
Income attributable to unvested stock-based compensation awards	(144)	(136)	(247)	(267)
Income available to common shareholders	20,927	17,850	39,650	33,879
Weighted-average common shares outstanding - basic (in shares)	39,324,000	36,346,000	38,948,000	34,804,000
Basic earnings per share (in dollars per share)	$ 0.53	$ 0.49	$ 1.02	$ 0.97
Earnings Per Share, Diluted [Abstract]
Net income	21,071	17,986	39,897	34,146
Income attributable to unvested stock-based compensation awards	(144)	(136)	(247)	(267)
Income available to common shareholders	$ 20,927	$ 17,850	$ 39,650	$ 33,879
Weighted-average common shares outstanding (in shares)	39,324,000	36,346,000	38,948,000	34,804,000
Assumed exercise of stock options (in shares)	463,000	438,000	501,000	486,000
Weighted-average shares - diluted (in shares)	39,787,000	36,784,000	39,449,000	35,290,000
Diluted earnings per share (in dollars per share)	$ 0.53	$ 0.49	$ 1.01	$ 0.96
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)					1,500,000	1,000,000