Stockholders' Equity (Details) (USD $)	0 Months Ended	3 Months Ended			139 Months Ended	0 Months Ended
	Mar. 13, 2015	Mar. 31, 2015		Mar. 31, 2014	Mar. 31, 2015	Feb. 13, 2015	May 16, 2013	Jul. 01, 2013	Apr. 15, 2013 director	Dec. 31, 2014	Dec. 31, 2013	Aug. 31, 2005	Aug. 08, 2013
Stockholders' Equity
Preferred stock, dividend rate (as a percent)		7.50%		7.50%
Preferred stock, shares issued		8,000,000			8,000,000					8,000,000
Preferred stock, par value (in dollars per share)		$ 0.01			$ 0.01					$ 0.01
Common stock, cash dividends declared (in dollars per share)	$ 0.20	$ 0.20		$ 0.20
Common stock, accrued dividends and DERs payable		$ 74,600,000			$ 74,600,000
Aggregate number of shares of common stock registered for sale under the plan		886,950,000			886,950,000					886,950,000
Number of shares authorized to be repurchased under the Repurchase Program											10,000,000	4,000,000
Repurchase of common stock, shares		0
Number of remaining shares authorized to be repurchased under the Repurchase Program (in shares)		6,616,355			6,616,355
DRSPP
Stockholders' Equity
Aggregate number of shares of common stock registered for sale under the plan													15,000,000
Shares of common stock authorized and available for issuance		7,000,000			7,000,000
Common shares issued through DRSPP		39,784			27,133,333
Net proceeds from shares issued through DRSPP		313,000			229,300,000
Series B
Stockholders' Equity
Dividend Declared Per Share, preferred stock (in dollars per share)						$ 0.46875
Preferred Stock | Series A
Stockholders' Equity
Preferred stock, dividend rate (as a percent)		8.50%
Preferred stock redeemed (in shares)							3,840,000
Payments to redeem preferred stock							97,000,000
Preferred stock, redemption price (in dollars per share)							$ 25.27153
Preferred stock, redemption value in excess of carrying value							3,900,000
Preferred stock, cash dividends (in dollars per share)							$ 0.27153
Preferred Stock | Series B
Stockholders' Equity
Preferred stock, dividend rate (as a percent)		7.50%							7.50%
Preferred stock, redemption price (in dollars per share)									$ 25.00
Preferred stock, cash dividends (in dollars per share)								$ 0.39583
Shares of common stock reclassified to preferred stock									8,050,000
Preferred stock, shares issued									8,000,000
Preferred stock, par value (in dollars per share)									$ 0.01
Preferred stock, liquidation preference (in dollars per share)		$ 25.00			$ 25.00				$ 25.00
Proceeds from issuance of preferred stock									$ 193,300,000
Number of additional directors that can be elected by preferred stock holders									2
Minimum percentage of preferred shareholders required for approval (percent)									66.67%
Repurchase of common stock, shares		0	[1]

[1] For the three months ended March 31, 2015, includes approximately $87,000 (11,074 shares) surrendered for tax purposes related to equity-based compensation awards.