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Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	101,912		106,201
Outstanding principal balance of residential mortgage loans serviced for others	$ 15,458,772,000		$ 16,228,449,000
Weighted average interest rate	3.78%		3.84%
Remaining term (in months)	279		280
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 101,172,000	$ 201,886,000	$ 201,886,000
Additions	9,830,000	5,441,000
Change in fair value due to principal payments	(11,961,000)	(8,019,000)
Change in fair value due to market assumption changes	33,874,000	(88,480,000)
Ending balance	$ 132,915,000	$ 110,828,000	$ 101,172,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)	9.13%		9.14%
Prepayment rate - based upon loan interest rate, original term and loan type, minimum	6.37%		9.41%
Prepayment rate - based upon loan interest rate, original term and loan type, maximum	17.80%		21.87%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)	$ 69		$ 69
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)	94		94
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)	1.04%		0.43%
Primary secondary mortgage rate spread	105		105
Delinquency rate	2.77%		3.54%

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- Definition

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

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Mortgage rate spread between the primary and secondary market.

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Indicates the number of mortgage loans being serviced.

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Dollar amount of principal outstanding on mortgage loans being serviced.

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

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

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

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

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

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

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

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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.

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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.

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Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Delinquency Rate

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

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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.

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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://www.xbrl.org/2003/role/disclosureRef
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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.

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

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