Servicing Rights - Key characteristics, inputs, and economic assumptions for residential mortgage loans and related sensitivity (Details) - Residential mortgage servicing rights - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Servicing Assets at Fair Value [Line Items]
Fair value of retained servicing assets	$ 11,877	$ 8,262	$ 5,170
Prepayment rate assumption (percent)	10.60%	9.50%
10% adverse change	$ (466)	$ (303)
20% adverse change	$ (898)	$ (587)
Discount rate (percent)	10.00%	10.00%
100 bps adverse change	$ (448)	$ (317)
200 bps adverse change	$ (863)	$ (610)