Stockholders' Equity (Details) (USD $)	0 Months Ended	3 Months Ended					3 Months Ended		0 Months Ended	3 Months Ended				3 Months Ended
	Jan. 29, 2014	Mar. 31, 2014	Mar. 31, 2013	Mar. 18, 2014	Dec. 31, 2013	Mar. 31, 2014 Atm Program [Member]	Mar. 31, 2014 Quarter 4 2013 [Member]	Mar. 31, 2014 Quarter 1 2014 [Member]	Feb. 18, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Mar. 31, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Mar. 27, 2018 Series B Cumulative Redeemable Preferred Stock [Member]	Mar. 18, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2013 Series B Cumulative Redeemable Preferred Stock [Member]	Mar. 31, 2014 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 1 2014 [Member]	Mar. 31, 2014 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 2 2014 [Member]	Mar. 27, 2018 Depository shares of Series B Cumulative Redeemable Preferred [Member]	Mar. 31, 2014 Depository shares of Series B Cumulative Redeemable Preferred [Member]
Class of Stock [Line Items]
Common stock, shares outstanding		153,017,311			152,983,101
At the market stock offering program, aggregate value of common stock						$ 600,000,000
At the market stock offering program remaining amount available for issuance						305,300,000
Shares of its Common Stock in connection with the redemption of an equal number of OP Units		18,528
Dividend payable date							Jan. 29, 2014	Apr. 30, 2014						Feb. 18, 2014	May 15, 2014
Dividend paid on common stock (in dollars per share)	$ 2.90								$ 32.8125
Dividend shareholder of record date							Dec. 31, 2013	Mar. 31, 2014							May 05, 2014
Dividends payable, date declared								Mar. 18, 2014							Mar. 18, 2014
Dividends Payable, Amount Per Share				$ 0.65								$ 32.8125
Series B, Shares Outstanding										80,000			80,000				8,000,000
Series B, Dividend Rate, Percentage										5.25%
Series B, Liquidation Preference Per Share										$ 2,500.00	$ 2,500.00		$ 2,500			$ 25.00	$ 25.00
Proceeds from Issuance of Series B		$ 0	$ 194,371,000
Ratio of depository shares to shares of Series B Preferred Stock										0.01