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Fair Value Measurements - Changes in Level 3 (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Changes in Level 3 |  |
Beginning balance |  | $ 2,268
Total gains or losses |  |
Included in other comprehensive income |  | 28
Purchases, issuances, sales, and settlements |  |
Settlements |  | (213)
Ending balance |  | 2,096
Changes in Level 3 (liabilities) |  |
Included in earnings (or changes in net assets) |  | 13
US States and Political Subdivisions Debt Securities [Member] |  |
Changes in Level 3 |  |
Beginning balance | $ 8,165 | 14,261
Total gains or losses |  |
Included in other comprehensive income | 171 | (699)
Purchases, issuances, sales, and settlements |  |
Purchases | 11,325 | 13,085
Settlements | (97) | (120)
Ending balance | 19,556 | 26,527
Changes in Level 3 (liabilities) |  |
Included in earnings (or changes in net assets) | (8) |
Mortgage Servicing Rights [Member] |  |
Changes in Level 3 |  |
Beginning balance | 7,357 | 6,944
Total gains or losses |  |
Included in earnings (or changes in net assets) |  | 417
Purchases, issuances, sales, and settlements |  |
Issuances | 177 | 291
Settlements | (98) | (111)
Ending balance | 6,715 | $ 7,541
Changes in Level 3 (liabilities) |  |
Included in earnings (or changes in net assets) | $ (721) |

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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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