Mortgage Servicing Rights - Mortgage Servicing Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Servicing Asset at Fair Value, Amount [Roll Forward]
Balance, beginning of period	$ 7,305
Additions for new MSR capitalized	760	$ 886
Changes in fair value:
Carrying value, March 31	8,039
Balance of mortgage loans serviced for others	$ 439,561		$ 406,291
MSR as a percentage of serviced loans	1.83%		1.80%
Mortgage servicing rights
Servicing Asset at Fair Value, Amount [Roll Forward]
Balance, beginning of period	$ 7,305	4,157
Additions for new MSR capitalized	760	886
Changes in fair value:
Due to changes in model inputs of assumptions	255	475
Other	(281)	(193)
Carrying value, March 31	$ 8,039	$ 5,325