Servicing Assets and Liabilities - 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, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Servicing Assets at Fair Value [Line Items]
Fair value of retained servicing assets	$ 13,565	$ 11,877	$ 8,262	$ 4,372
Prepayment rate assumption (percent)	14.10%	10.60%
10% adverse change	$ (662)	$ (466)
20% adverse change	$ (1,270)	$ (898)
Discount rate (percent)	10.00%	10.00%
100 bps adverse change	$ (467)	$ (448)
200 bps adverse change	$ (900)	$ (863)