Mortgage Servicing Rights - Summary of Carrying Value Under the Amortization Method (Details) - Mortgage Servicing Rights - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Mortgage Servicing Rights Accounted for Under the Amortization Method (Rollforward)
Balance at Beginning of Year	$ 23,896	$ 23,020	$ 23,168
Servicing Rights that Resulted From Asset Transfers	3,592	4,485	2,470
Amortization	(4,902)	(3,609)	(2,618)
Valuation Allowance Recovery (Provision)	(3,892)
Balance at End of Year	18,694	23,896	23,020
Valuation Allowance:
Valuation Allowance Recovery (Provision)	(3,892)
Balance at End of Year	(3,892)
Fair Value:
Balance at Beginning of Year	25,714	29,218	26,716
Balance at End of Year	$ 18,694	$ 25,714	$ 29,218