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Fair Value Measurements - Changes in Level 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes in Level 3
Beginning balance	$ 3,119
Total gains or losses
Included in earnings (or changes in net assets)	40
Included in other comprehensive income	21	$ (82)
Purchases, issuances, sales, and settlements
Settlements	(912)
Ending balance		3,119
Changes in Level 3 (liabilities)
Beginning balance	(3,119)
Ending balance	2,268	3,119
Collateralized loan obligations
Purchases, issuances, sales, and settlements
Transfers into Level 3		3,201
States and political subdivisions
Changes in Level 3
Beginning balance	22,226	111
Total gains or losses
Included in other comprehensive income	(796)	87
Purchases, issuances, sales, and settlements
Purchases	16,712	14,296
Settlements	(23,881)	(81)
Ending balance	14,261	22,226
Transfers into Level 3		7,813
Mortgage servicing rights
Changes in Level 3
Beginning balance	6,489	5,847
Total gains or losses
Included in earnings (or changes in net assets)	(270)	(215)
Purchases, issuances, sales, and settlements
Issuances	1,257	1,561
Settlements	(532)	(704)
Ending balance	$ 6,944	$ 6,489

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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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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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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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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Fair value of 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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