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Key Assumptions Used in Calculating Fair Value of Residential Mortgage Servicing Rights (Detail) - $ / LoanPerYear | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Mortgage Loans on Real Estate [Line Items] |  |
Expected weighted average life | 87 months | 82 months
Constant prepayment speed | 9.81% | 8.70%
Discount rate | 12.00% | 10.05%
Primary mortgage rate to refinance | 4.02% | 4.11%
Cost to service per loan per year, current | 70 | 64
30-59 days or less delinquent |  |
Mortgage Loans on Real Estate [Line Items] |  |
Cost to service per loan per year | 220 | 214
60-89 days delinquent |  |
Mortgage Loans on Real Estate [Line Items] |  |
Cost to service per loan per year | 370 | 364
90-119 days delinquent |  |
Mortgage Loans on Real Estate [Line Items] |  |
Cost to service per loan per year | 470 | 464
120 days or more delinquent |  |
Mortgage Loans on Real Estate [Line Items] |  |
Cost to service per loan per year | 870 | 864

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- Definition Cost To Service Loan Per Loan Per Year Current + References No definition available. + Details
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- Definition Discount rate which is used to value residual cash flows generated by financial assets of a securitization, asset-backed financing arrangement, or similar transfer regardless of when the transfer occurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719 + Details
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- Definition The stated interest rate on the mortgage loan receivable or the weighted average interest rate on a group of loans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-29) -URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule IV) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + 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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