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Fair Value Measurements - Changes in Level 3 (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes in Level 3
Transfers into Level 3	$ 0	$ 0
Transfers out of Level 3	0	0
Collateralized loan obligations
Changes in Level 3
Beginning balance		2,268,000
Transfers out of Level 3		(1,308,000)
Total gains or losses
Included in earnings (or changes in net assets)		35,000
Included in other comprehensive income		40,000
Purchases, issuances, sales, and settlements
Settlements		(1,035,000)
US States and Political Subdivisions Debt Securities [Member]
Changes in Level 3
Beginning balance	8,165,000	14,261,000
Total gains or losses
Included in earnings (or changes in net assets)	(32,000)
Included in other comprehensive income	726,000	(746,000)
Purchases, issuances, sales, and settlements
Purchases	17,938,000	22,046,000
Settlements	(21,378,000)	(27,396,000)
Ending balance	5,419,000	8,165,000
Mortgage Servicing Rights [Member]
Changes in Level 3
Beginning balance	7,357,000	6,944,000
Total gains or losses
Included in earnings (or changes in net assets)	(1,953,000)	(181,000)
Purchases, issuances, sales, and settlements
Issuances	1,240,000	1,146,000
Settlements	(709,000)	(552,000)
Ending balance	$ 5,935,000	$ 7,357,000

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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