Stockholders' Equity (Series B) (Details)													12 Months Ended
	Nov. 18, 2020 $ / shares	Aug. 12, 2020 $ / shares	Jul. 01, 2020 $ / shares	Nov. 15, 2019 $ / shares	Aug. 09, 2019 $ / shares	May 20, 2019 $ / shares	Feb. 15, 2019 $ / shares	Nov. 26, 2018 $ / shares	Aug. 20, 2018 $ / shares	May 17, 2018 $ / shares	Feb. 20, 2018 $ / shares	Apr. 15, 2013 $ / shares shares	Dec. 31, 2020 director quarter $ / shares shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares	Dec. 31, 2017 $ / shares
Class of Stock [Line Items]
Maximum quarters without dividends to get voting rights, in quarters | quarter													6
Minimum percentage of preferred shareholders required for approval													66.67%
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares) | shares													8,000,000	8,000,000
Preferred stock, par value (in dollars per share)													$ 0.01	$ 0.01
Preferred stock, dividend rate													7.50%	7.50%
Preferred stock, cash dividends declared (in dollars per share)	$ 0.46875	$ 0.46875	$ 0.93750	$ 0.46875	$ 0.46875	$ 0.46875	$ 0.46875	$ 0.46875	$ 0.46875	$ 0.46875	$ 0.46875		$ 1.875	$ 1.875	$ 1.875
Series B Preferred Stock | Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares) | shares												8,000,000.0
Preferred stock, par value (in dollars per share)												$ 0.01
Preferred stock, liquidation preference (in dollars per share)												$ 25.00	$ 25.00	$ 25.00	$ 25.00	$ 25.00
Preferred stock, dividend rate												7.50%	7.50%	7.50%	7.50%	7.50%
Preferred stock, redemption price (in dollars per share)												$ 25.00
Number of additional directors that can be elected by preferred stock holders | director													2