EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended
	Jan. 31, 2012	Apr. 30, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jul. 22, 2009
EARNINGS PER SHARE [Abstract]
Weighted-average anti-dilutive stock options outstanding (in shares)			300,000	500,000	600,000
Basic earnings per share [Abstract]
Net income			$ 78,829	$ 77,068	$ 73,142
Income attributable to unvested stock-based compensation awards			(433)	(499)	(553)
Income available to common shareholders			78,396	76,569	72,589
Weighted-average common shares outstanding - basic (in shares)			40,000,000	39,192,000	35,767,000
Basic earnings per share (in dollars per share)			$ 1.96	$ 1.95	$ 2.03
Diluted earnings per share [Abstract]
Net income			78,829	77,068	73,142
Income attributable to unvested stock-based compensation awards			(433)	(499)	(553)
Income available to common shareholders			78,396	76,569	72,589
Weighted-average common shares outstanding (in shares)			40,000,000	39,192,000	35,767,000
Assumed exercise of stock options (in shares)			504,000	479,000	415,000
Weighted-average shares - diluted (in shares)			40,504,000	39,671,000	36,182,000
Diluted earnings per share (in dollars per share)			$ 1.94	$ 1.93	$ 2.01
Cash dividends declared per share (in dollars per share)			$ 1.10	$ 1.06	$ 1.00
Common stock issuance	57,500		15,239	64,145	5,351
Common stock issuance (in shares)	2,130,000	3,350,000
Net proceeds from offerings	$ 54,900			$ 54,917
Stock Repurchase Program [Abstract]
Number of common shares authorized to be repurchased (in shares)			2,000,000	2,000,000	1,500,000	1,000,000