Stockholders' Equity (Details)						6 Months Ended
	May. 15, 2015 $ / shares	Apr. 30, 2015 $ / shares	Feb. 17, 2015 $ / shares	Jan. 28, 2015 $ / shares	Jun. 03, 2014 USD ($) yr	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 27, 2018 $ / shares	Jun. 17, 2015 $ / shares	Dec. 31, 2014 USD ($) $ / shares shares
Class of Stock [Line Items]
Common stock, shares outstanding | shares						153,473,931			153,113,945
Shares of its Common Stock in connection with the redemption of an equal number of OP Units (in shares) | shares						321,700
Shares of Common Stock upon the exercise of options to purchase Common Stock by certain employees (in shares) | shares						11,447
Dividend paid on common stock (in dollars per share)		$ 0.65		$ 5.15
Dividends Payable, Amount Per Share								$ 0.65
Common Stock, Value, Issued | $						$ 1,535,000			$ 1,531,000
New ATM program [Member]
Class of Stock [Line Items]
At the market stock offering program, aggregate value of common stock | $					$ 600,000,000
At Market Stock Offering Program Maximum Length Of Sale In Years | yr					3
Common Stock, Value, Issued | $						$ 0
Quarter 4 2014 [Member]
Class of Stock [Line Items]
Dividend payable date						Jan. 28, 2015
Dividend shareholder of record date						Dec. 31, 2014
Quarter 1 2015 [Member]
Class of Stock [Line Items]
Dividend payable date						Apr. 30, 2015
Dividend shareholder of record date						Mar. 31, 2015
Quarter 2 2015 [Member]
Class of Stock [Line Items]
Dividend payable date						Jul. 31, 2015
Dividend shareholder of record date						Jun. 30, 2015
Dividends payable, date declared						Jun. 17, 2015
Series B Cumulative Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Dividend paid on common stock (in dollars per share)	$ 32.8125		$ 32.8125
Dividends Payable, Amount Per Share								$ 32.8125
Series B, Shares Outstanding (in shares) | shares						80,000			80,000
Series B, Dividend Rate, Percentage						5.25%
Series B, Liquidation Preference Per Share (dollars per share)						$ 2,500.00			$ 2,500.00
Ratio of depository shares to shares of Series B Preferred Stock						0.01
Series B Cumulative Redeemable Preferred Stock [Member] | Quarter 1 2015 [Member]
Class of Stock [Line Items]
Dividend payable date						Feb. 17, 2015
Series B Cumulative Redeemable Preferred Stock [Member] | Quarter 2 2015 [Member]
Class of Stock [Line Items]
Dividend payable date						May 15, 2015
Series B Cumulative Redeemable Preferred Stock [Member] | Quarter 3 2015 [Member]
Class of Stock [Line Items]
Dividend payable date						Aug. 17, 2015
Dividend shareholder of record date						Aug. 05, 2015
Dividends payable, date declared						Jun. 17, 2015
Depository shares of Series B Cumulative Redeemable Preferred [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares) | shares						8,000,000
Series B, Liquidation Preference Per Share (dollars per share)						$ 25.00	$ 25.00
Subsequent Event [Member] | Series B Cumulative Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Series B, Liquidation Preference Per Share (dollars per share)							$ 2,500.00