Stockholders' Equity (Narrative) (Details)									1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended	202 Months Ended
	Aug. 12, 2020 $ / shares	Aug. 06, 2020 $ / shares	Jul. 01, 2020 $ / shares	Jun. 15, 2020 USD ($) $ / shares shares	Mar. 02, 2020 USD ($)	Feb. 28, 2020 $ / shares shares	Feb. 14, 2020 $ / shares	Apr. 15, 2013 $ / shares shares	Mar. 31, 2020 quarter director	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 $ / shares	Jun. 30, 2019 $ / shares	Mar. 31, 2019 $ / shares	Sep. 30, 2020 USD ($) quarter director $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 $ / shares shares	Jun. 30, 2020 USD ($) shares	Oct. 15, 2019 shares	Aug. 16, 2019 USD ($)	Dec. 31, 2013 shares	Aug. 31, 2005 shares
Stockholders' Equity
Common stock, cash dividends declared (in dollars per share)		$ 0.05								$ 0.05	$ 0.20	$ 0.20	$ 0.20
Proceeds from issuance of redeemable preferred stock | $														$ 275,000,000	$ 0
Aggregate number of shares of common stock authorized (in shares) | shares										874,300,000				874,300,000		886,950,000
Number of shares authorized to be repurchased under the Repurchase Program (in shares) | shares																				10,000,000.0	4,000,000.0
Number of remaining shares authorized to be repurchased under the Repurchase Program (in shares) | shares										6,616,355				6,616,355
Number of shares called by warrant (in shares) | shares				37,039,106
Proceeds from issuance of warrants | $				$ 495,000,000.0										$ 14,041,000	$ 0
DRSPP
Stockholders' Equity
Aggregate number of shares of common stock authorized (in shares) | shares																		9,000,000.0
Shares of common stock authorized and available for issuance (in shares) | shares										8,800,000				8,800,000
Common shares issued through DRSPP (in shares) | shares										4,374				137,740			34,516,508
Net proceeds from shares issued through DRSPP | $										$ 11,688				$ 752,095			$ 287,300,000
Series B Preferred Stock
Stockholders' Equity
Preferred Stock, dividend rate														7.50%		7.50%
Preferred stock, shares issued (in shares) | shares										8,000,000				8,000,000		8,000,000
Preferred stock par value (usd per share)										$ 0.01				$ 0.01		$ 0.01
Dividend declared per share, preferred stock (in dollars per share)	$ 0.46875		$ 0.9375				$ 0.46875			$ 1.40625	$ 0.46875	$ 0.46875	$ 0.46875
Series C Preferred Stock
Stockholders' Equity
Preferred Stock, dividend rate														6.50%
Preferred stock, shares issued (in shares) | shares										11,000,000				11,000,000
Preferred stock par value (usd per share)										$ 0.01				$ 0.01
Dividend declared per share, preferred stock (in dollars per share)										0.93889
Amount of preferred dividends in arrears (USD per share)	$ 0.40625													$ 0.53264
Preferred Stock | Series B Preferred Stock
Stockholders' Equity
Preferred Stock, dividend rate								7.50%						7.50%	7.50%
Preferred stock, shares issued (in shares) | shares								8,000,000.0
Preferred stock par value (usd per share)								$ 0.01
Preferred stock, liquidation preference (in dollars per share)								25.00		$ 25.00				$ 25.00		$ 25.00
Preferred stock, redemption price (in dollars per share)								$ 25.00
Maximum quarters without dividends to get voting rights, in quarters | quarter														6
Number of additional directors that can be elected by preferred stock holders | director														2
Percentage required for making material changes								66.67%
Preferred Stock | Series C Preferred Stock
Stockholders' Equity
Preferred Stock, dividend rate						6.50%
Preferred stock, shares issued (in shares) | shares						11,000,000.0
Preferred stock par value (usd per share)						$ 0.01
Preferred stock, liquidation preference (in dollars per share)						25.00
Preferred stock, redemption price (in dollars per share)						$ 25.00
Maximum quarters without dividends to get voting rights, in quarters | quarter									6
Number of additional directors that can be elected by preferred stock holders | director									2
Shares reclassified to redeemable capital stock (in shares) | shares						12,650,000
Proceeds from issuance of redeemable preferred stock | $					$ 266,000,000.0
Warrant
Stockholders' Equity
Proceeds from issuance of warrants | $				$ 14,000,000.0
At The Market
Stockholders' Equity
At-the-market, maximum potential proceeds | $																			$ 400,000,000.0
Sales commission of gross sales price																			2.00%
Number of shares issued (in shares) | shares										0
Value remaining outstanding for future offerings | $										$ 390,000,000.0				$ 390,000,000.0
LIBOR | Preferred Stock | Series C Preferred Stock
Stockholders' Equity
Debt instrument, basis spread on variable rate						5.345%
Exercise Price Range One
Stockholders' Equity
Warrant exercise price (usd per share)				$ 1.66
Exercise Price Range Two
Stockholders' Equity
Warrant exercise price (usd per share)				$ 2.08
Debt
Stockholders' Equity
Proceeds from issuance of warrants | $				$ 481,000,000.0