Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

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Amount of undisbursed portion of financing receivable balance. Excludes financing receivable covered under loss sharing agreement.

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Number of bank branches where the Bank conducts its activities

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Summary of Significant Accounting Policies (Details) $ in Thousands	Dec. 31, 2020 USD ($) branch	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Accounting Policies [Line Items]
Number of bank branches \| branch	234
Increase (decrease) to retained earnings for the cumulative effect of adopting ASC 326	$ 2,061,767	$ 2,014,133	$ 2,031,127	$ 2,032,995
Cash collateral	54,800	97,600
Loans in process	1,679,972	1,456,072
Financing Receivable
Accounting Policies [Line Items]
Loans in process	3,011,286	2,738,095
Retained Earnings
Accounting Policies [Line Items]
Increase (decrease) to retained earnings for the cumulative effect of adopting ASC 326	$ 1,443,280	$ 1,420,906	$ 1,365,397	1,335,909
Cumulative Effect, Period of Adoption, Adjustment
Accounting Policies [Line Items]
Increase (decrease) to retained earnings for the cumulative effect of adopting ASC 326				(21,945)
Cumulative Effect, Period of Adoption, Adjustment \| Retained Earnings
Accounting Policies [Line Items]
Increase (decrease) to retained earnings for the cumulative effect of adopting ASC 326				$ (21,945)