Fair Value Measurements - Schedule of Balance Sheet Grouping Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Liabilities
Net deferred loan fees	$ 29,000	$ 13,900
Carrying Amount \| Level 1
Assets [Abstract]
Cash and cash equivalents	432,887	243,474
Carrying Amount \| Level 3
Assets [Abstract]
Loans, net, excluding fair valued loans, loans held for sale and impaired loans	8,738,617	8,472,777
Carrying Amount \| Level 2
Liabilities
Time deposits	1,282,978	2,095,676
FHLB advances and other borrowings	195,000	340,000
Securities sold under repurchase agreements	65,506	68,992
Subordinated debentures and subordinated notes payable	108,832	108,636
Fair Value \| Level 1
Assets [Abstract]
Cash and cash equivalents	432,887	243,474
Fair Value \| Level 3
Assets [Abstract]
Loans, net, excluding fair valued loans, loans held for sale and impaired loans	8,768,314	8,533,612
Fair Value \| Level 2
Liabilities
Time deposits	1,287,814	2,101,239
FHLB advances and other borrowings	204,715	351,517
Securities sold under repurchase agreements	65,506	68,992
Subordinated debentures and subordinated notes payable	$ 96,424	$ 101,164

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
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