Certain Transfers of Financial Assets - MSRs Key Metrics (Details) - Residential mortgage - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Residential Mortgage Servicing Rights
Servicing Asset at Fair Value, Amount	$ 103,725	$ 88,502
Composition of Loans Serviced for Others	100.00%	100.00%
Weighted average remaining term (years)	25 years 8 months 15 days	25 years 8 months
Modeled prepayment speed	8.19%	7.98%
Decline in fair value due to a 10% adverse change	$ (3,497)	$ (2,918)
Decline in fair value due to a 20% adverse change	(6,796)	(5,643)
Decline in fair value due to a 10% adverse change	(4,299)	(3,619)
Decline in fair value due to a 20% adverse change	$ (8,223)	$ (6,889)
Weighted Average
Residential Mortgage Servicing Rights
Weighted average discount rate	9.95%	9.91%
Fixed-rate mortgage loans
Residential Mortgage Servicing Rights
Composition of Loans Serviced for Others	99.55%	99.47%
Adjustable-rate mortgage loans
Residential Mortgage Servicing Rights
Composition of Loans Serviced for Others	0.45%	0.53%

Assumptions and estimates in determining the impairment of capitalized Mortgage Servicing Rights.

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- Definition

Composition of Loans Serviced for Others

+ References

No definition available.

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- Definition

The hypothetical financial impact of a 10 percent adverse change of the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ 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 (c)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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- Definition

The hypothetical financial impact of a 10 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

+ Details

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- Definition

The hypothetical financial impact of a 20 percent adverse change of the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

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- Definition

The hypothetical financial impact of a 20 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

+ References

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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

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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

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- Definition

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

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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.

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