Shareholders' Equity - Dividends Declared Per Share and Related Tax Characterizations (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Series A Cumulative Redeemable Preferred Stock
Dividends Per Share
Dividends declared, preferred stock (usd per share)	$ 1.9376	$ 1.9376
Series A Cumulative Redeemable Preferred Stock | December 15, 2015
Dividends Per Share
Dividends declared, preferred stock (usd per share)		0.4844
Series A Cumulative Redeemable Preferred Stock | Ordinary Dividends
Dividends Per Share
Dividends declared, preferred stock (usd per share)	1.9376	1.9376
Series A Cumulative Redeemable Preferred Stock | Capital Gain Distributions
Dividends Per Share
Dividends declared, preferred stock (usd per share)	0	0
Series A Cumulative Redeemable Preferred Stock | Carry Forward
Dividends Per Share
Dividends declared, preferred stock (usd per share)	0	0
Series B Cumulative Redeemable Preferred Stock
Dividends Per Share
Dividends declared, preferred stock (usd per share)	1.9376
Series B Cumulative Redeemable Preferred Stock | December 15, 2015
Dividends Per Share
Dividends declared, preferred stock (usd per share)	0.4844	0.4844
Series B Cumulative Redeemable Preferred Stock | Ordinary Dividends
Dividends Per Share
Dividends declared, preferred stock (usd per share)	1.9376
Series B Cumulative Redeemable Preferred Stock | Capital Gain Distributions
Dividends Per Share
Dividends declared, preferred stock (usd per share)	0	0
Series B Cumulative Redeemable Preferred Stock | Carry Forward
Dividends Per Share
Dividends declared, preferred stock (usd per share)	0	0
Common Stock
Dividends Per Share
Dividends declared, common stock (usd per share)	1.6	1.7
Common Stock | December 15, 2015
Dividends Per Share
Dividends declared, common stock (usd per share)		0.40
Common Stock | Ordinary Dividends
Dividends Per Share
Dividends declared, common stock (usd per share)	1.85784	1.615469
Common Stock | Capital Gain Distributions
Dividends Per Share
Dividends declared, common stock (usd per share)	0	0
Common Stock | Carry Forward
Dividends Per Share
Dividends declared, common stock (usd per share)	$ 0	$ 0.25784