Stockholders' Equity (Details) (USD $)	0 Months Ended		1 Months Ended				3 Months Ended				1 Months Ended					3 Months Ended	12 Months Ended	0 Months Ended	3 Months Ended	115 Months Ended	1 Months Ended	104 Months Ended
	Mar. 28, 2013	Mar. 04, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Mar. 31, 2013		Mar. 31, 2012	Aug. 31, 2005	Apr. 30, 2013 Preferred Stock Series A	Dec. 31, 2012 Preferred Stock Series A	Oct. 31, 2012 Preferred Stock Series A	Jul. 31, 2012 Preferred Stock Series A	Apr. 30, 2012 Preferred Stock Series A	Mar. 31, 2013 Preferred Stock Series A Q Director	Dec. 31, 2012 Preferred Stock Series A	May 16, 2013 Subsequent event Preferred Stock Series A Forecast	Mar. 31, 2013 DRSPP	Mar. 31, 2013 DRSPP	Dec. 31, 2008 Controlled Equity Offering Program	Mar. 31, 2013 Controlled Equity Offering Program
Stockholders' Equity
Preferred stock, dividend rate (as a percent)																8.50%	8.50%
Preferred stock, shares issued												3,840,000				3,840,000	3,840,000
Preferred stock, shares outstanding												3,840,000				3,840,000	3,840,000
Preferred stock, par value (in dollars per share)												$ 0.01				$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)																$ 25.00
Preferred stock, redemption price (in dollars per share)																$ 25.00		$ 25.00
Minimum number of quarters for which failure to pay dividends on the preferred stock will give rise to voting rights																6
Number of additional directors that can be elected by preferred stock holders																2
Minimum percentage of preferred shareholders required for approval																66.67%
Preferred stock, cash dividends (in dollars per share)							$ 0.53125				$ 0.53125	$ 0.53125	$ 0.53125	$ 0.53125	$ 0.53125
Outstanding preferred stock that will be redeemed (in shares)																		3,840,000
Common stock, cash dividends declared (in dollars per share)	$ 0.22	$ 0.50	$ 0.20	$ 0.21	$ 0.23	$ 0.24	$ 0.72	[1]	$ 0.24
Common stock, accrued dividends and DERs payable	$ 79,200,000	$ 180,100,000
Aggregate number of shares of common stock registered for sale under the plan			895,000,000				895,000,000												10,000,000	10,000,000
Shares of common stock authorized and available for issuance																			7,200,000	7,200,000
Shares issued																			834,038	17,362,063		30,144,815
Net proceeds																			7,367,194	151,200,000		194,908,570
Fees and commissions paid to Cantor																						$ 4,189,247
Maximum number of shares that may be offered and sold through Cantor																					40,000,000
Number of shares authorized to be repurchased under the Repurchase Program										4,000,000
Number of Remaining shares authorized to be repurchased under the Repurchase Program (in shares)							2,759,709

[1] Includes a special dividend of $0.50 per share.