Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Available-for-sale securities, pledged securities	$ 0	$ 1,295,225,428
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, dividend rate, percentage	8.75%
Preferred stock, liquidation preference	$ 25	$ 25
Preferred stock, shares issued	1,610,000	1,610,000
Preferred stock, shares outstanding	1,610,000	1,610,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	450,000,000	450,000,000
Common stock, shares issued	23,683,164	22,143,758
Common stock, shares outstanding	23,683,164	22,143,758
Assets of consolidated VIEs	$ 23,949,942	$ 1,255,404,335
Liabilities of consolidated VIEs	$ 19,561,943	$ 1,228,295,517