Servicing Rights - Key Assumptions and the Sensitivity of the Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing Assets at Fair Value [Line Items]
Aggregate portfolio principal balance	$ 557,583	$ 406,291
Mortgage servicing rights, at fair value	$ 10,821	$ 7,305
MSR as a percentage of serviced loans	1.94%	1.80%
Mortgage servicing rights
Servicing Assets at Fair Value [Line Items]
Aggregate portfolio principal balance	$ 557,583	$ 406,291
Weighted average rate of note	3.91%	3.77%
Conditional prepayment rate	7.70%	9.00%
Impact of 1 percent adverse change in prepayment rate, percent	19.35%	23.33%
Impact of 2 percent adverse change in prepayment rate, percent	20.95%	25.25%
Average discount rate	9.94%	9.45%
Impact of 1 percent adverse change in discount rate, percent	8.94%	8.45%
Impact of 2 percent adverse change in discount rate, percent	7.94%	7.45%
Mortgage servicing rights, at fair value	$ 10,821	$ 7,305	$ 4,157	$ 1,654
Impact of 1 percent adverse change, fair value of mortgage servicing rights	7,115	4,343
Impact of 2 percent adverse change, fair value of mortgage servicing rights	$ 6,829	$ 4,109
MSR as a percentage of serviced loans	1.94%	1.80%
Impact of 1 percent adverse change, percentage of mortgage servicing rights	1.28%	1.07%
Impact of 2 percent adverse change, percentage of mortgage servicing rights	1.22%	1.01%