Fair Value Measurements - Schedule of Fair Values for Balance Sheet Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Liabilities
Unamortized discount on acquired loans	$ 33,800	$ 13,900
Level 1 \| Carrying Amount
Assets
Cash and cash equivalents	311,585	243,474
Level 1 \| Fair Value
Assets
Cash and cash equivalents	311,585	243,474
Level 3 \| Carrying Amount
Assets
Loans, net, excluding fair valued loans, loans held for sale and impaired loans	8,974,255	8,472,777
Level 3 \| Fair Value
Assets
Loans, net, excluding fair valued loans, loans held for sale and impaired loans	9,091,344	8,533,612
Level 2 \| Carrying Amount
Liabilities
Time deposits	1,433,538	2,095,676
FHLB advances and other borrowings	355,000	340,000
Securities sold under repurchase agreements	70,362	68,992
Subordinated debentures and subordinated notes payable	108,792	108,636
Level 2 \| Fair Value
Liabilities
Time deposits	1,440,485	2,101,239
FHLB advances and other borrowings	373,811	351,517
Securities sold under repurchase agreements	70,362	68,992
Subordinated debentures and subordinated notes payable	$ 96,330	$ 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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- Definition

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)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-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))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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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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- Definition

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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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