Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Apr. 24, 2018	Jan. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Preferred Stock Fair Value			$ 335,979		$ 263,317
Sale of Stock, Number of Shares Issued in Transaction			54,750
Proceeds from Issuance or Sale of Equity		$ 52,500
Payments of Stock Issuance Costs			$ 1,061	$ 16,112
Series B Preferred Stock
Class of Stock [Line Items]
Preferred Stock Fair Value			$ 171,917		146,649
Shares Issued, Price Per Share			$ 1,000
Preferred Stock, Shares Issued			155,000
Preferred Stock, Shares Outstanding			155,000
Preferred Stock, Dividend Rate, Percentage			17.396%
Preferred Stock, Redemption Term			8 years
Series C Preferred Stock
Class of Stock [Line Items]
Preferred Stock Fair Value			$ 83,541		76,096
Shares Issued, Price Per Share			$ 1,000
Preferred Stock, Shares Issued			55,000
Preferred Stock, Shares Outstanding			55,000
Preferred Stock, Dividend Rate, Percentage			17.396%
Preferred Stock, Redemption Term			8 years
Series D Preferred Stock
Class of Stock [Line Items]
Preferred Stock Fair Value			$ 2,258		6,672
Shares Issued, Price Per Share			$ 1.00
Preferred Stock, Shares Issued			100
Preferred Stock, Shares Outstanding			100
Preferred Stock, Redemption Term			8 years
Series E Preferred Stock
Class of Stock [Line Items]
Preferred Stock Fair Value			$ 39,456		33,900
Shares Issued, Price Per Share			$ 1,000
Preferred Stock, Shares Issued			90,000
Preferred Stock, Shares Outstanding			37,500
Preferred Stock, Dividend Rate, Percentage			15.646%
Preferred Stock, Redemption Term			6 years
Series E-1 Preferred Stock
Class of Stock [Line Items]
Preferred Stock Fair Value			$ 38,807		$ 0
Sale of Stock, Number of Shares Issued in Transaction			17,500
Shares Issued, Price Per Share			$ 1,000
Proceeds from Issuance or Sale of Equity	$ 17,500		$ 17,500
Preferred Stock, Shares Issued			35,728
Preferred Stock, Shares Outstanding			35,728
Preferred Stock, Dividend Rate, Percentage			15.646%
Preferred Stock, Redemption Term			6 years
Series E-1 Preferred Stock Tranche 2
Class of Stock [Line Items]
Sale of Stock, Number of Shares Issued in Transaction	18,228		18,228
Shares Issued, Price Per Share			$ 960
Series E-1 Preferred Stock Tranche 3
Class of Stock [Line Items]
Sale of Stock, Number of Shares Issued in Transaction			19,022
Shares Issued, Price Per Share			$ 920