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%

[Line Items] for The key economic assumptions used to value servicing assets.

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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

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- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

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