Per Share Data (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended
	Jan. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Per Share Data
Net Income available to Common Stockholders - Basic		$ 381,555	$ 311,675	$ 339,936	$ 283,138	$ 315,383	$ 254,921	$ 215,445	$ 645,410	$ 1,316,304	$ 1,431,159	$ 1,021,462
Effect of dilutive securities:
Impact to General Partner's interest in Operating Partnership from all dilutive securities and options												39
Net Income available to Common Stockholders - Diluted										$ 1,316,304	$ 1,431,159	$ 1,021,501
Weighted Average Shares Outstanding - Basic		310,434,337	310,332,777	310,261,278	309,986,506	303,137,350	304,107,489	303,252,359	295,693,410	310,255,168	303,137,350	293,504,064
Effect of stock options (in shares)										50	1,072	69,408
Weighted Average Shares Outstanding - Diluted		310,434,337	310,332,777	310,261,278	309,986,709	303,138,422	304,108,559	303,253,401	295,694,520	310,255,218	303,138,422	293,573,472
Dividends paid per common share (in dollars per share)										$ 4.65	$ 4.10	$ 3.50
Percent taxable as ordinary income										97.50%	99.50%	98.30%
Percent taxable as long-term capital gains										2.50%	0.50%	1.70%
Total percentage of dividends paid										100.00%	100.00%	100.00%
Dividends declared per common share (in dollars per share)	$ 1.25