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Mortgage Servicing Rights - Narrative (Details) - Mortgage loans - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract] |  |  |
Mortgage servicing rights, fair value | $ 40,100,000 | $ 35,700,000 |
Servicing asset at fair value, assumptions used to estimate fair value, weighted average life | 7 years 3 months 17 days | 8 years |
Impairment reversals | $ 90,000 | $ 40,000 | $ 100,000
Permanent impairment charged against carrying value | $ 0 | $ 0 | $ 0
Minimum |  |  |
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract] |  |  |
Servicing assets at fair value, assumptions used to estimate fair value, discount rate | 9.50% | 9.60% |
Servicing assets at fair value, assumptions used to estimate fair value, prepayment speed | 0.50% | 0.50% |
Maximum |  |  |
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract] |  |  |
Servicing assets at fair value, assumptions used to estimate fair value, discount rate | 11.30% | 11.40% |
Servicing assets at fair value, assumptions used to estimate fair value, prepayment speed | 1.80% | 1.50% |

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- Definition Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746 + Details
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- Definition Discount rate used to estimate the fair value of servicing assets and servicing liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746 + Details
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- Definition Estimated rate of prepayments of principal on servicing assets and servicing liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746 + Details
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- Definition Weighted average life of financial assets and financial liabilities, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746 + Details
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- Definition Amount of decrease in the valuation allowance for impairment of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer from write-downs charged against the allowance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746 + Details
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- Definition Amount of decrease in the valuation allowance for impairment of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer from recoveries recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (e)(2) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746 + Details
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