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Mortgage Servicing Rights (Economic Assumptions) (Details) - $ / loans | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017
Servicing Asset Key Economic Assumptions [Line Items] |  |
Weighted average constant prepayment rate | 8.38% | 10.93%
Weighted average cost to service a loan | 72.67 | 64.03
Conventional fixed loans |  |
Servicing Asset Key Economic Assumptions [Line Items] |  |
Discount rate | 10.06% | 9.41%
All loans excluding conventional fixed loans |  |
Servicing Asset Key Economic Assumptions [Line Items] |  |
Discount rate | 11.06% | 10.41%

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- Definition [Line Items] for The key economic assumptions used to value servicing assets. + References No definition available. + Details
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- Definition Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Cost to Service Loans + References No definition available. + Details
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- Definition Discount rate used to estimate the fair value of servicing assets and servicing liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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://fasb.org/us-gaap/role/ref/legacyRef -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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- Details
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- Details
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