Stockholders' Equity (Details) (USD $)	0 Months Ended		6 Months Ended				0 Months Ended			6 Months Ended			0 Months Ended		6 Months Ended			6 Months Ended
	Apr. 30, 2014	Jan. 29, 2014	Jun. 30, 2014	Jun. 30, 2013	Jun. 19, 2014	Dec. 31, 2013	Jun. 03, 2014 New ATM program [Member] Y	Jun. 30, 2014 New ATM program [Member]	Jun. 02, 2014 Atm Program [Member]	Jun. 30, 2014 Quarter 4 2013 [Member]	Jun. 30, 2014 Quarter 1 2014 [Member]	Jun. 30, 2014 Quarter 2 2014 [Member]	May 15, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Feb. 18, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Jun. 30, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Jun. 19, 2014 Series B Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2013 Series B Cumulative Redeemable Preferred Stock [Member]	Jun. 30, 2014 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 1 2014 [Member]	Jun. 30, 2014 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 2 2014 [Member]	Jun. 30, 2014 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 3 2014 [Member]	Mar. 27, 2018 Depository shares of Series B Cumulative Redeemable Preferred [Member]	Jun. 30, 2014 Depository shares of Series B Cumulative Redeemable Preferred [Member]	Mar. 27, 2018 Subsequent Event [Member] Series B Cumulative Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, shares outstanding			153,092,574			152,983,101
At the market stock offering program, aggregate value of common stock							$ 600,000,000		$ 600,000,000
At Market Stock Offering Program Maximum Length Of Sale In Years							3
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			66,612
Shares of Common Stock upon the exercise of options to purchase Common Stock by certain employees (in shares)			17,124
Dividend payable date										Jan. 29, 2014	Apr. 30, 2014	Jul. 31, 2014						Feb. 18, 2014	May 15, 2014	Aug. 15, 2014
Dividend paid on common stock (in dollars per share)	$ 0.65	$ 2.90											$ 32.8125	$ 32.8125
Dividend shareholder of record date										Dec. 31, 2013	Mar. 31, 2014	Jun. 30, 2014								Aug. 05, 2014
Dividends payable, date declared												Jun. 19, 2014								Jun. 19, 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				$ 25.00	$ 25.00	$ 2,500.00
Proceeds from Issuance of Series B			0	193,920,000
Ratio of depository shares to shares of Series B Preferred Stock															0.01
Common Stock, Value, Issued			$ 1,531,000			$ 1,530,000		$ 0