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ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2019
Allowance for Credit Losses - Debt Securities [Abstract] |  |
Accrued interest receivable on available-for-sale debt securities | $ 13,900 |
Loans [Abstract] |  |
Accrued interest receivable on loans | $ 19,300 |
Number of days past due for loans to be placed on nonaccrual status | 90 days |
Contract Balances [Abstract] |  |
Accounts receivable | $ 25,200 | $ 26,800
Unbilled fee revenue | 8,700 | 7,500
Unearned revenue | 3,100 | 1,800
New Accounting Pronouncements [Abstract] |  |
Retained earnings | $ 902,148 | 882,851
Allowance for credit losses |  | 49,911
Consumer Installment Loans [Member] |  |
Loans [Abstract] |  |
Number of days past due after which loans are charged off to the extent outstanding principal balance exceeds fair value of collateral/property | 90 days |
Consumer Mortgage [Member] |  |
Loans [Abstract] |  |
Number of days past due after which loans are charged off to the extent outstanding principal balance exceeds fair value of collateral/property | 180 days |
Consumer Mortgage [Member] | Minimum [Member] |  |
New Accounting Pronouncements [Abstract] |  |
Typical contract term | 10 years |
Consumer Mortgage [Member] | Maximum [Member] |  |
New Accounting Pronouncements [Abstract] |  |
Typical contract term | 30 years |
Home Equity [Member] |  |
Loans [Abstract] |  |
Number of days past due after which loans are charged off to the extent outstanding principal balance exceeds fair value of collateral/property | 180 days |
Home Equity [Member] | Maximum [Member] |  |
New Accounting Pronouncements [Abstract] |  |
Typical contract term | 30 years |
ASU 2016-13 [Member] |  |
New Accounting Pronouncements [Abstract] |  |
Allowance for credit losses | $ 56,497 | 52,453
ASU 2016-13 [Member] | Cumulative Effect Adjustment [Member] |  |
New Accounting Pronouncements [Abstract] |  |
Retained earnings |  | 500
Increase in allowance for credit losses |  | 1,400
Adjustment to loans |  | 3,100
Increase in other liabilities |  | 1,200
Allowance for credit losses |  | $ 3,100

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- Definition Refers to the number of days past due after which loans are charged off to the extent outstanding principal balance exceeds fair value of collateral/property, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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