Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	128,463		128,463		132,463
Outstanding principal balance of residential mortgage loans serviced for others	$ 21,046,136,000		$ 21,046,136,000		$ 21,658,335,000
Weighted average interest rate	3.99%		3.99%		3.99%
Remaining term (in months)			290 months		293 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 208,308,000	$ 278,719,000	$ 259,254,000	$ 252,867,000	$ 252,867,000
Additions, net	9,882,000	8,968,000	24,821,000	28,688,000
Change in fair value due to principal payments	(11,936,000)	(8,986,000)	(27,600,000)	(25,783,000)
Change in fair value due to market assumption changes	(12,593,000)	5,972,000	(62,814,000)	28,901,000
Ending balance	$ 193,661,000	$ 284,673,000	$ 193,661,000	$ 284,673,000	$ 259,254,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)			9.82%		9.90%
Prepayment rate - based upon loan interest rate, original term and loan type, minimum			8.31%		8.05%
Prepayment rate - based upon loan interest rate, original term and loan type, maximum			17.22%		15.74%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)			$ 68		$ 67
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)			94		93
Loan servicing costs - annually per loan based upon loan type, delinquent, minimum (in dollars per loan)			150		150
Loan servicing costs - annually per loan based upon loan type, delinquent, maximum (in dollars per loan)			500		500
Loan servicing costs - annually per loan based upon loan type, foreclosure, minimum (in dollars per loan)			1,000		1,000
Loan servicing costs - annually per loan based upon loan type, foreclosure, maximum (in dollars per loan)			$ 4,000		$ 4,000
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)			1.51%		2.57%
Primary secondary mortgage rate spread	102		102		105

The decrease in fair value as a result of loan runoff.

No definition available.

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- Definition

Mortgage rate spread between the primary and secondary market.

+ References

No definition available.

+ Details

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- Definition

Indicates the number of mortgage loans being serviced.

+ References

No definition available.

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- Definition

Dollar amount of principal outstanding on mortgage loans being serviced.

+ References

No definition available.

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- Definition

Represents the weighted average remaining term of mortgage loans being serviced fro others.

+ References

No definition available.

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- Definition

Servicing Assets at Fair Value Assumptions Used to Estimate Fair Value Delinquent Loan Service Cost Minimum

+ References

No definition available.

+ Details

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- Definition

Servicing Assets At Fair Value Assumptions Used to Estimate Fair Value Delinquent

+ References

No definition available.

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- Definition

The escrow earning rate used to estimate the fair value of servicing assets, based on rates paid on deposit accounts.

+ References

No definition available.

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- Definition

Servicing Assets At Fair Value Assumptions Used to Estimate Fair Value Foreclosure Loan Service Cost Maximum

+ References

No definition available.

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- Definition

Servicing Assets at Fair Value Assumptions Used to Estimate Fair Value Foreclosure Loan Service Cost Minimum

+ References

No definition available.

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- Definition

The maximum cost to service a performing loan for the period used as a variable in estimating fair value.

+ References

No definition available.

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- Definition

The minimum cost to service a performing loan for the period used as a variable in estimating fair value.

+ References

No definition available.

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- Definition

The maximum estimated speed of prepayments of principal on financial assets which may be one of the factors applied in estimating the fair value of servicing assets.

+ References

No definition available.

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- Definition

The minimum estimated speed of prepayments of principal on financial assets which may be one of the factors applied in estimating the fair value of servicing assets.

+ References

No definition available.

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- Definition

-- None. No documentation exists for this element. --

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No definition available.

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- Definition

Represents the weighted average interest rate of loans servicedf for others as of the balance sheet date.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in fair value from changes in the assumptions or model used to calculate the fair value of a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

No definition available.

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- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

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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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
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-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122596-111746

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