Stockholder's Equity - Federal Tax Treatment of Distributions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Unrecaptured Section 1250 gain, percent of capital gain	100.00%	0.00%	19.00%
Common Stock
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.4536470	$ 0.5100000	$ 0.5000000
Dividend, federal income tax treatment (percent)	100.00%	100.00%	100.00%
Common Stock | Ordinary Income [Member]
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.4520850	$ 0.4789478	$ 0.4607500
Dividend, federal income tax treatment (percent)	99.66%	93.91%	92.15%
Common Stock | Return Of Capital [Member]
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.0000000	$ 0.0000000	$ 0.0000000
Dividend, federal income tax treatment (percent)	0.00%	0.00%	0.00%
Common Stock | Capital Gain [Member]
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.0015620	$ 0.0310522	$ 0.0392500
Dividend, federal income tax treatment (percent)	0.34%	6.09%	7.85%
Preferred Stock
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.5507800
Dividend, federal income tax treatment (percent)	100.00%
Preferred Stock | Ordinary Income [Member]
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.5488840
Dividend, federal income tax treatment (percent)	99.66%
Preferred Stock | Return Of Capital [Member]
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.0000000
Dividend, federal income tax treatment (percent)	0.00%
Preferred Stock | Capital Gain [Member]
Class of Stock [Line Items]
Dividend, federal income tax treatment (per share)	$ 0.0018960
Dividend, federal income tax treatment (percent)	0.34%