Fair Value Measurements - Assets Measured at Fair Value on a Nonrecurring Basis (Details) - Fair Value, measurements, nonrecurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Impaired loans measured at fair value on a nonrecurring basis
Impaired loans	$ 11,050	$ 27,348
OREO	1,788	2,820
Mortgage servicing rights	57,600	53,208
Total financial assets	70,438	83,376
Level 1
Impaired loans measured at fair value on a nonrecurring basis
Impaired loans	0	0
OREO	0	0
Mortgage servicing rights	0	0
Total financial assets	0	0
Level 2
Impaired loans measured at fair value on a nonrecurring basis
Impaired loans	0	0
OREO	0	0
Mortgage servicing rights	0	0
Total financial assets	0	0
Level 3
Impaired loans measured at fair value on a nonrecurring basis
Impaired loans	11,050	27,348
OREO	1,788	2,820
Mortgage servicing rights	57,600	53,208
Total financial assets	$ 70,438	$ 83,376