Condensed Consolidated Balance Sheet (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Common shares	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000	100,000,000
Common stock, shares issued	43,781,684	38,647,943	29,796,601
Common stock, shares outstanding	43,781,684	38,647,943	29,796,601
Preferred Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	100,000,000	100,000,000
Preferred Stock, Shares Issued	4,600,000	4,600,000
Preferred Stock, Shares Outstanding	4,600,000	4,600,000
Preferred Stock, Dividend Rate, Percentage	6.75%	6.75%
Preferred Stock, Liquidation Preference, Value	$ 115,000	$ 115,000
Investments, at fair value, Cost			$ 2,970,306,000
Financial derivative-assets, at fair value, Net Cost			22,526,000
Repurchase agreements, cost			61,274,000
Investments sold short, at fair value, Proceeds			844,604,000
Financial derivatives–assets, at fair value-Net Proceeds			19,019,000
Other secured borrowings, Proceeds			114,100,000
Other secured financing, at fair value-Proceeds			$ 298,706,000