Preferred Stock (Schedule of Preferred Stock ) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	May 01, 2017	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Preferred stock		$ 263,317	$ 0
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock		$ 146,649	0
Preferred shares issued at $0.01 par value (in shares)	155,000
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred Stock, Shares Outstanding		155,000
Share issued, price per share (in dollars per share)	$ 1,000
Preferred Stock, Dividend Rate, Percentage		16.737%
Preferred stock redemption term	8 years
Series B Preferred Stock | 12 - 24 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	105.00%
Series B Preferred Stock | 24 - 36 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	103.00%
Series B Preferred Stock | Minimum
Class of Stock [Line Items]
Dividend rate, component two	4.75%
Series B Preferred Stock | Maximum
Class of Stock [Line Items]
Dividend rate, component two	12.50%
Series B Preferred Stock | London Interbank Offered Rate (LIBOR)
Class of Stock [Line Items]
Dividend rate, component one, basis spread on variable rate	3.00%
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock		$ 76,096	0
Preferred shares issued at $0.01 par value (in shares)	55,000
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred Stock, Shares Outstanding		55,000
Share issued, price per share (in dollars per share)	$ 1,000
Preferred Stock, Dividend Rate, Percentage		16.737%
Preferred stock redemption term	8 years
Series C Preferred Stock | 0 - 12 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	65.00%
Series C Preferred Stock | Minimum
Class of Stock [Line Items]
Dividend rate, component two	4.75%
Series C Preferred Stock | Maximum
Class of Stock [Line Items]
Dividend rate, component two	12.50%
Series C Preferred Stock | London Interbank Offered Rate (LIBOR)
Class of Stock [Line Items]
Dividend rate, component one, basis spread on variable rate	3.00%
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock		$ 6,672	0
Preferred shares issued at $0.01 par value (in shares)	100
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred Stock, Shares Outstanding		100
Share issued, price per share (in dollars per share)	$ 1.00
Preferred stock redemption term	8 years
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock		$ 33,900	$ 0
Preferred shares issued at $0.01 par value (in shares)	90,000
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred Stock, Shares Outstanding		37,500
Share issued, price per share (in dollars per share)	$ 1,000
Dividend rate, component two	8.50%
Preferred Stock, Dividend Rate, Percentage		14.987%
Preferred stock redemption term	6 years
Series E Preferred Stock | 0 - 12 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	106.50%
Series E Preferred Stock | 12 - 24 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	103.50%
Series E Preferred Stock | London Interbank Offered Rate (LIBOR)
Class of Stock [Line Items]
Dividend rate, component one, basis spread on variable rate	5.25%
Series F Preferred Stock
Class of Stock [Line Items]
Preferred shares issued at $0.01 par value (in shares)	240,500
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred Stock, Shares Outstanding		0
Share issued, price per share (in dollars per share)	$ 1,000
Preferred stock redemption term	6 years
Series F Preferred Stock | Refinancing date
Class of Stock [Line Items]
Preferred stock redemption rights	101.00%
Series F Preferred Stock | 0 - 12 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	106.50%
Series F Preferred Stock | 12 - 24 months from closing date
Class of Stock [Line Items]
Preferred stock redemption rights	103.50%
Series F Preferred Stock | London Interbank Offered Rate (LIBOR)
Class of Stock [Line Items]
Dividend rate, component one, basis spread on variable rate	6.25%