EARNINGS PER SHARE - Reconciliation of weighted average shares outstanding (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
EARNINGS PER SHARE
Net income available for stockholders:	$ 63,283	$ 40,416	$ 102,671	$ 75,492
Less: Dividends paid	(22,898)	(22,015)	(45,883)	(44,030)
Undistributed earnings	$ 40,385	$ 18,401	$ 56,788	$ 31,462
Basic shares outstanding:
Common stock	211,611	211,707	211,522	211,790
Restricted shares of common stock	3,613	4,176	3,677	4,249
Basic shares outstanding, total	215,224	215,883	215,199	216,039
Diluted shares outstanding:
Common stock	211,611	211,707	211,522	211,790
Dilutive effect of stock based awards	1,014	812	1,081	1,151
Diluted shares outstanding excluding restricted shares of common stock, total	212,625	212,519	212,603	212,941
Restricted shares of common stock	3,613	4,176	3,677	4,249
Diluted shares outstanding, total	216,238	216,695	216,280	217,190