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Mortgage Banking Activities, Mortgage Servicing Rights (Details) | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($)
Summary of Mortgage Servicing Rights [Abstract] |  |  |  |  |
Number of residential mortgage loans serviced for others | 116,232 |  | 116,232 |  | 126,828
Outstanding principal balance of residential mortgage loans serviced for others | $ 18,038,428,000 |  | $ 18,038,428,000 |  | $ 20,727,106,000
Weighted average interest rate | 3.96% |  | 3.96% |  | 3.98%
Remaining term (in months) |  |  | 283 |  | 289
Servicing Asset at Fair Value, Amount [Roll Forward] |  |  |  |  |
Beginning balance | $ 110,828,000 | $ 238,193,000 | $ 201,886,000 | $ 259,254,000 | $ 259,254,000
Additions | 8,465,000 | 8,751,000 | 13,906,000 | 14,939,000 |
Disposals | (10,801,000) | 0 | (10,801,000) | 0 |
Change in fair value due to principal payments | (9,760,000) | (9,081,000) | (17,779,000) | (15,664,000) |
Change in fair value due to market assumption changes | (761,000) | (29,555,000) | (89,241,000) | (50,221,000) |
Ending balance | $ 97,971,000 | $ 208,308,000 | $ 97,971,000 | $ 208,308,000 | $ 201,886,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract] |  |  |  |  |
Discount rate - risk-free rate plus a market premium (in hundredths) |  |  | 9.67% |  | 9.81%
Prepayment rate - based upon loan interest rate, original term and loan type, minimum |  |  | 9.04% |  | 8.28%
Prepayment rate - based upon loan interest rate, original term and loan type, maximum |  |  | 30.87% |  | 16.05%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan) |  |  | $ 69 |  | $ 68
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) |  |  | 0.33% |  | 1.73%
Primary secondary mortgage rate spread | 105 |  | 105 |  | 104
Delinquency rate |  |  | 4.51% |  | 2.73%

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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 The escrow earning rate used to estimate the fair value of servicing assets, based on rates paid on deposit accounts. + References No definition available. + Details
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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. + Details
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