Servicing Rights - Key Assumptions and the Sensitivity of the Fair Value (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Servicing Assets at Fair Value [Line Items]
Aggregate portfolio principal balance	$ 655,733	$ 659,048
Base
Fair value MSR	$ 10,589	$ 11,920
Percentage of MSR (percent)	1.61%	1.81%
Mortgage servicing rights
Servicing Assets at Fair Value [Line Items]
Aggregate portfolio principal balance	$ 655,733	$ 659,048
Weighted average rate of note (percent)	3.74%	3.90%
Base
Constant prepayment rate (percent)	14.31%	10.61%
Discount rate (percent)	7.75%	8.52%
Fair value MSR	$ 10,589	$ 11,920	$ 10,721	$ 11,206	$ 10,836	$ 10,821
Percentage of MSR (percent)	1.61%	1.81%
1.0% Adverse Rate Change
Constant prepayment rate (percent)	42.34%	26.25%
Discount rate (percent)	6.75%	7.52%
Fair value MSR	$ 4,748	$ 7,005
Percentage of MSR (percent)	0.72%	1.06%
2.0% Adverse Rate Change
Constant prepayment rate (percent)	50.41%	28.39%
Discount rate (percent)	5.75%	6.52%
Fair value MSR	$ 3,808	$ 6,625
Percentage of MSR (percent)	0.58%	1.01%