Fair Value of Assets and Liabilities - Impact on the fair value of liabilities assuming hypothetical changes in certain inputs (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Increase/(Decrease) in Fair Value of Servicing Liabilities
Impact of 100 basis point increase in reversal rate	$ 1,932	$ 1,586
Impact of 100 basis point decrease in reversal rate	(1,833)	(1,524)
Cost of servicing sensitivity:
Increase of 10 basis points	364	331
Decrease of 10 basis points	(364)	(331)
Discount rate sensitivity:
Increase of 1%	(26)	(25)
Decrease of 1%	27	26
Recovery period sensitivity:
Increase of one year	380	316
Decrease of one year	$ (422)	$ (351)