Stockholders' Equity (Details) (USD $)	0 Months Ended												3 Months Ended			9 Months Ended					3 Months Ended	9 Months Ended	121 Months Ended	1 Months Ended	110 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	0 Months Ended	3 Months Ended					9 Months Ended	3 Months Ended	0 Months Ended		3 Months Ended	9 Months Ended
	Sep. 26, 2013		Aug. 01, 2013		Jun. 28, 2013	Mar. 28, 2013	Mar. 04, 2013		Dec. 12, 2012	Sep. 28, 2012	Jun. 27, 2012	Mar. 23, 2012	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012	Aug. 31, 2005	Sep. 30, 2013 DRSPP	Sep. 30, 2013 DRSPP	Sep. 30, 2013 DRSPP	Dec. 31, 2008 Controlled Equity Offering Program	Sep. 30, 2013 Controlled Equity Offering Program	Sep. 30, 2013 Series A	Dec. 31, 2012 Series A	Sep. 30, 2013 Series B	Dec. 31, 2012 Series B	May 16, 2013 Preferred Stock Series A	Sep. 30, 2013 Preferred Stock Series A	Mar. 31, 2013 Preferred Stock Series A	Dec. 31, 2012 Preferred Stock Series A	Sep. 30, 2012 Preferred Stock Series A	Mar. 31, 2012 Preferred Stock Series A	Sep. 30, 2013 Preferred Stock Series A	Sep. 30, 2013 Preferred Stock Series A Accrued and Unpaid Dividends	Aug. 22, 2013 Preferred Stock Series B	Apr. 15, 2013 Preferred Stock Series B	Sep. 30, 2013 Preferred Stock Series B	Sep. 30, 2013 Preferred Stock Series B director quarter
Stockholders' Equity
Preferred stock, dividend rate (as a percent)																										8.50%	8.50%	7.50%	0.00%							8.50%					7.50%
Preferred stock redeemed (in shares)																														3,840,000						3,840,000
Preferred stock, shares outstanding																										0	3,840,000	8,000,000	0		0					0
Payments to redeem preferred stock																														$ 97,000,000
Preferred stock, redemption price (in dollars per share)																														$ 25.27153										$ 25.00	$ 25.00
Preferred stock, redemption value in excess of carrying value																																				3,900,000
Preferred stock, cash dividends (in dollars per share)																															$ 0.53125	$ 0.53125	$ 0.53125	$ 0.53125	$ 0.53125		$ 0.27153
Shares of common stock reclassified to preferred stock																																							8,050,000
Preferred stock, shares issued																										0	3,840,000	8,000,000	0										8,000,000
Preferred stock, par value (in dollars per share)																										$ 0.01	$ 0.01	$ 0.01	$ 0										$ 0.01
Preferred stock, liquidation preference (in dollars per share)																															$ 25.00					$ 25.00			$ 25.00	$ 25.00	$ 25.00
Proceeds from issuance of preferred stock																200,000,000		0																					193,300,000
Preferred stock, dividends payable (in dollars per share)																																								$ 0.39583	$ 0.39583
Preferred Stock, Dividends Per Share, Declared																																						$ 0.46875
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%
Common stock, cash dividends declared (in dollars per share)	$ 0.22	[1]	$ 0.28	[2]	$ 0.22	$ 0.22	$ 0.50	[3]	$ 0.20	$ 0.21	$ 0.23	$ 0.24	$ 0.50	[4]	$ 0.21	$ 1.44	[4],[5]	$ 0.68
Common stock, accrued dividends and DERs payable													81,171,000			81,171,000
Aggregate number of shares of common stock registered for sale under the plan													886,950,000			886,950,000			895,000,000		15,000,000	15,000,000	15,000,000
Shares of common stock authorized and available for issuance																					12,900,000	12,900,000	12,900,000
Shares issued																					3,669,147	8,168,287	24,696,312		30,144,815																8,000,000
Net proceeds																					27,209,940	67,821,145	211,600,000		194,908,570
Fees and commissions paid to Cantor																6,684,000		0							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
Stock Repurchase Program Stock Repurchased and Retired During Period Shares													3,800			3,800
Stock Repurchase Program Stock Repurchased and Retired During Period Value													$ 27,041			$ 27,000
Stock Repurchased and Retired During Period Average Cost Per Share													$ 7.12
Number of Remaining shares authorized to be repurchased under the Repurchase Program (in shares)													2,755,909			2,755,909

[1] At September 30, 2013, the Company had accrued dividends and DERs payable of $81.2 million related to the common stock dividend declared on September 26, 2013.

[2] Reflects the special cash dividend on common stock declared on August 1, 2013.

[3] Reflects the special cash dividend on common stock declared on March 4, 2013.

[4] Includes a special dividend of $0.28 per share declared on August 1, 2013.

[5] Includes a special dividend of $0.50 per share declared on March 4, 2013.