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Mortgage Banking Activities, Components of Loans Held For Sale (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Schedule of Residential Mortgage Loans Held For Sale [Line Items] |  |  |
Number of days for past due for loan to be considered nonperforming (in days) | 90 days | 90 days | 90 days
Residential mortgage loans held for sale, nonperforming | $ 0 | $ 0 | $ 0
Credit losses recognized on residential mortgage loans held for sale | 0 | 0 | 0
Components of Residential Mortgage Loans Held for Sale [Abstract] |  |  |
Unpaid principal balance | 169,095 | 261,868 | 212,525
Residential mortgage loans held for sale, Fair value | 169,226 | 265,783 | 215,113
Total residential mortgage loans held for sale and mortgage loan commitments, net of forward sales contracts | $ 175,866 | $ 275,643 | $ 221,378
Residential Mortgage Loan Commitments [Member] | Not Designated as Hedging Instrument [Member] |  |  |
Schedule of Residential Mortgage Loans Held For Sale [Line Items] |  |  |
General number of days outstanding for residential mortgage commitments, minimum (in days) | 60 days | 60 days | 60 days
General number of days outstanding for residential mortgage commitments, maximum (in days) | 90 days | 90 days | 90 days
Components of Residential Mortgage Loans Held for Sale [Abstract] |  |  |
Notional | $ 197,752 | $ 334,337 | $ 222,919
Derivative, Net fair value | $ 5,027 | $ 9,066 | $ 6,523
Forward sales contracts [Member] | Not Designated as Hedging Instrument [Member] |  |  |
Schedule of Residential Mortgage Loans Held For Sale [Line Items] |  |  |
General number of days for delivery of loans, for which the price is set by forward sales contracts, minimum (in days) | 60 days | 60 days | 60 days
General number of days for delivery for loans, for which the price is set by forward sales contracts, maximum (in days) | 90 days | 90 days | 90 days
Components of Residential Mortgage Loans Held for Sale [Abstract] |  |  |
Notional | $ 330,876 | $ 524,878 | $ 380,159
Derivative, Net fair value | $ 1,613 | $ 794 | $ (258)

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- Definition Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522 + Details
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