Mortgage Servicing Rights - Key Assumptions and the Sensitivity of the Fair Value (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Transfers and Servicing [Abstract]
Aggregate portfolio principal balance	$ 472,190	$ 406,291
Weighted average rate of note	3.80%	3.77%
Conditional prepayment rate	7.75%	9.00%
Impact of 1 percent adverse change in prepayment rate, percent	20.22%	23.33%
Impact of 2 percent adverse change in prepayment rate, percent	21.95%	25.25%
Discount rate	9.89%	9.45%
Impact of 1 percent adverse change in discount rate, percent	8.89%	8.45%
Impact of 2 percent adverse change in discount rate, percent	7.89%	7.45%
Mortgage servicing rights	$ 8,733	$ 7,305
Impact of 1 percent adverse change, fair value of mortgage servicing rights	5,445	4,343
Impact of 2 percent adverse change, fair value of mortgage servicing rights	$ 5,189	$ 4,109
MSR as a percentage of serviced loans	1.85%	1.80%
Impact of 1 percent adverse change, percentage of mortgage servicing rights	1.15%	1.07%
Impact of 2 percent adverse change, percentage of mortgage servicing rights	1.10%	1.01%