EARNINGS PER SHARE - Reconciliation of weighted average shares outstanding (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
EARNINGS PER SHARE
Net income available for stockholders:	$ 40,416	$ 72,260	$ 75,492	$ 153,015
Less: Dividends paid	(22,015)	(17,512)	(44,030)	(35,083)
Undistributed earnings	$ 18,401	$ 54,748	$ 31,462	$ 117,932
Basic shares outstanding:
Common stock	211,707	210,331	211,790	210,683
Restricted shares of common stock	4,176	4,562	4,249	4,558
Basic shares outstanding, Total	215,883	214,893	216,039	215,241
Diluted shares outstanding:
Common stock	211,707	210,331	211,790	210,683
Dilutive effect of stock based awards	812	1,234	1,151	1,539
Diluted shares outstanding excluding restricted shares of common stock, Total	212,519	211,565	212,941	212,222
Restricted shares of common stock	4,176	4,562	4,249	4,558
Diluted shares outstanding, Total	216,695	216,127	217,190	216,780