Shareholders' Equity (Details) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock, shares authorized	50,000,000				50,000,000				50,000,000
Preferred stock, par value	$ 0.01				$ 0.01				$ 0.01
Preferred stock, shares issued	5,888,680				4,571,937				5,888,680
Preferred Stock, Liquidation Preference Per Share	$ 25.00								$ 25.00
Preferred Stock, Dividend Payment Terms									The Series A Preferred Stock pays a cumulative cash dividend equivalent to 8.50% of the $25.00 liquidation preference per share each year and the Series B Preferred Stock pays a cumulative cash dividend equivalent to 7.625% of the $25.00 liquidation preference per share each year.
Dividends declared per common share	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.21	$ 0.21	$ 0.21	$ 0.21
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	8,000,000								8,000,000
Preferred stock, shares issued	2,300,000				2,300,000				2,300,000
Preferred Stock, Dividend Rate, Percentage									8.50%
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	7,000,000								7,000,000
Preferred stock, shares issued	3,588,680				2,271,937				3,588,680
Preferred Stock, Dividend Rate, Percentage									7.625%
Preferred Stock
Class of Stock [Line Items]
Dividends Payable, Date to be Paid	Jan. 15, 2018
Dividends Payable, Date of Record	Jan. 01, 2018
Common Stock
Class of Stock [Line Items]
Dividends Payable, Date to be Paid	Jan. 31, 2018
Dividends Payable, Date of Record	Dec. 29, 2017