Equity - Series F Distributions Paid on a Percentage Basis (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Ordinary dividends	60.00%	95.00%	75.90%
Nondividend distributions	37.00%	0.00%	0.00%
Capital gain distributions	3.00%	5.00%	24.10%
Total	100.00%	100.00%	100.00%
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Ordinary dividends	95.00%	95.00%	75.90%
Nondividend distributions	0.00%	0.00%	0.00%
Capital gain distributions	5.00%	5.00%	24.10%
Total	100.00%	100.00%	100.00%