EARNINGS PER SHARE - Reconciliation of weighted average shares outstanding (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
EARNINGS PER SHARE
Net income available for stockholders:	$ 64,885	$ 53,760	$ 167,556	$ 129,252
Less: Dividends paid	(22,939)	(21,892)	(68,822)	(65,923)
Undistributed earnings	$ 41,946	$ 31,868	$ 98,734	$ 63,329
Basic shares outstanding:
Common stock	211,604	210,899	211,552	211,493
Restricted shares of common stock	3,598	4,169	3,648	4,222
Basic shares outstanding, total	215,202	215,068	215,200	215,715
Diluted shares outstanding:
Common stock	211,604	210,899	211,552	211,493
Dilutive effect of stock based awards	1,132	1,074	1,116	1,147
Diluted shares outstanding excluding restricted shares of common stock, total	212,736	211,973	212,668	212,640
Restricted shares of common stock	3,598	4,169	3,648	4,222
Diluted shares outstanding, total	216,334	216,142	216,316	216,862