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Fair Value Measurements - Changes in Level 3 (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Changes in Level 3
Beginning balance		$ 3,119
Total gains or losses
Included in other comprehensive income		7
Purchases, issuances, sales, and settlements
Settlements		(666)
Ending balance		2,492
Changes in Level 3 (liabilities)
Included in earnings (or changes in net assets)		32
Collateralized loan obligations
Changes in Level 3
Beginning balance	$ 2,268
Total gains or losses
Included in other comprehensive income	34
Purchases, issuances, sales, and settlements
Settlements	(770)
Ending balance	1,564
Changes in Level 3 (liabilities)
Included in earnings (or changes in net assets)	32
States and political subdivisions
Changes in Level 3
Beginning balance	14,261	22,226
Total gains or losses
Included in other comprehensive income	(805)	(501)
Purchases, issuances, sales, and settlements
Purchases	20,421	10,994
Settlements	(24,366)	(20,359)
Ending balance	9,511	12,360
Mortgage servicing rights
Changes in Level 3
Beginning balance	6,944	6,489
Total gains or losses
Included in earnings (or changes in net assets)		(354)
Purchases, issuances, sales, and settlements
Issuances	997	951
Settlements	(446)	(402)
Ending balance	8,131	$ 6,684
Changes in Level 3 (liabilities)
Included in earnings (or changes in net assets)	$ 636

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Amount of gain (loss) recognized in the income statement for 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 gain (loss) recognized in other comprehensive income (loss) for 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 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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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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Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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