Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Available-for-sale securities, pledged securities	$ 1,309,061,643	$ 876,121,505
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%	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	22,139,258	17,539,258
Common stock, shares outstanding	22,139,258	17,539,258
Assets of consolidated VIEs	$ 1,280,093,874	$ 1,369,120,941
Liabilities of consolidated VIEs	$ 1,253,353,428	$ 1,344,404,080