Borrowings - Long-term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Long-term borrowings
Long-term borrowings	$ 122,029	$ 127,029
Repurchase Agreement with Third-party Correspondent
Long-term borrowings
Effective interest rate (as a percent)	3.55%
Interest rate, (as a percent)	7.00%
Interest rate, basis for adjustments	7.00 percent minus three-month LIBOR
Long-term borrowings	$ 5,000	$ 5,000
Non-Recourse Revolving Bank Line of Credit
Long-term borrowings
Long-term borrowings	$ 75,030
Non-Recourse Revolving Bank Line of Credit | LIBOR
Long-term borrowings
Variable rate basis	one-month LIBOR
Minimum | Non-Recourse Revolving Bank Line of Credit | LIBOR
Long-term borrowings
Variable rate, basis spread (as a percent)	2.00%
Maximum | Non-Recourse Revolving Bank Line of Credit | LIBOR
Long-term borrowings
Variable rate, basis spread (as a percent)	2.25%
Convertible Advances | FHLB Advances
Long-term borrowings
Long-term borrowings	$ 30,000
Fixed Rate Hybrid Advances | FHLB Advances
Long-term borrowings
Long-term borrowings	$ 17,000