EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of basic and diluted net income and distributions per common share
Net income	$ 77,013	$ 111,964	$ 71,205	$ 88,048	$ 76,981	$ 39,820	$ 107,504	$ 93,767	$ 348,230	$ 318,072	$ 371,064
Less: Dividends and undistributed earnings allocated to participating securities									1,116	1,082	3,108
Net income applicable to common shareholders									347,114	316,990	367,956
Effect of dilutive securities:
Interest on convertible senior notes									3,234
Net income applicable to common shareholders for diluted earnings per share									$ 350,348	$ 316,990	$ 367,956
Basic:
Basic weighted average shares outstanding (in shares)	177,906,000	177,862,000	177,809,000	177,775,000	177,759,000	177,723,000	177,674,000	177,075,000	177,838,000	177,560,000	157,936,000
Net income per share (in dollars per share)	$ 0.43	$ 0.63	$ 0.40	$ 0.49	$ 0.43	$ 0.22	$ 0.60	$ 0.53	$ 1.95	$ 1.79	$ 2.33
Diluted:
Basic weighted average shares outstanding (in shares)	177,906,000	177,862,000	177,809,000	177,775,000	177,759,000	177,723,000	177,674,000	177,075,000	177,838,000	177,560,000	157,936,000
Dilutive effect of convertible senior notes (in shares)									9,585,000	3,337,000	835,000
Diluted weighted average shares outstanding (in shares)	202,371,000	183,431,000	181,642,000	182,247,000	179,675,000	180,220,000	182,393,000	181,292,000	187,423,000	180,897,000	158,771,000
Net income per share (in dollars per share)	$ 0.40	$ 0.61	$ 0.39	$ 0.48	$ 0.43	$ 0.22	$ 0.59	$ 0.51	$ 1.87	$ 1.75	$ 2.32
Dividends
Distributions declared per common share (in dollars per share)									$ 0.86	$ 0.67	$ 0.43
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									1,932,279	1,932,279	1,932,279