Allowance for Losses on Loans - Activity in Allowance for Loan Losses by Loan Portfolio Segment and Class (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	$ 171,384	$ 172,653	$ 171,300	$ 166,955
Charge-offs	(281)	(47)	(1,870)	(407)
Recoveries	876	1,178	5,049	5,736
Provision & Transfers	1,500	(2,000)	1,500	1,000
Ending Allowance	170,979	170,784	170,979	170,784
Provisions & Transfers	(1,000)	(3,000)	(3,500)	(1,500)
Unfunded commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions & Transfers	2,500	1,000	5,000	2,500
Commercial loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	129,440	125,444	125,375	109,923
Charge-offs	(28)	(11)	(1,475)	(31)
Recoveries	42	507	3,122	3,259
Ending Allowance	130,859	123,519	130,859	123,519
Provisions & Transfers	1,405	(2,421)	3,837	10,368
Commercial loans \| Multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	14,463	17,776	16,949	13,853
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending Allowance	12,574	17,668	12,574	17,668
Provisions & Transfers	(1,889)	(108)	(4,375)	3,815
Commercial loans \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	24,682	26,822	23,437	22,516
Charge-offs	0	0	(529)	0
Recoveries	23	485	820	2,731
Ending Allowance	25,300	23,885	25,300	23,885
Provisions & Transfers	595	(3,422)	1,572	(1,362)
Commercial loans \| Commercial & industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	53,903	47,794	45,957	38,665
Charge-offs	(27)	(11)	(943)	(31)
Recoveries	8	13	72	74
Ending Allowance	54,924	45,538	54,924	45,538
Provisions & Transfers	1,040	(2,258)	9,838	6,830
Commercial loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	22,707	22,549	25,585	24,156
Charge-offs	0	0	0	0
Recoveries	0	0	2,179	0
Ending Allowance	25,834	24,823	25,834	24,823
Provisions & Transfers	3,127	2,274	(1,930)	667
Commercial loans \| Land - acquisition & development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	13,685	10,503	13,447	10,733
Charge-offs	(1)	0	(3)	0
Recoveries	11	9	51	454
Ending Allowance	12,227	11,605	12,227	11,605
Provisions & Transfers	(1,468)	1,093	(1,268)	418
Consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	41,944	47,209	45,925	57,032
Charge-offs	(253)	(36)	(395)	(376)
Recoveries	834	671	1,927	2,477
Ending Allowance	40,120	47,265	40,120	47,265
Provisions & Transfers	(2,405)	(579)	(7,337)	(11,868)
Consumer loans \| Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	3,129	3,248	4,907	3,555
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending Allowance	3,354	3,522	3,354	3,522
Provisions & Transfers	225	274	(1,553)	(33)
Consumer loans \| Single-family residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	28,992	35,108	30,978	45,186
Charge-offs	0	0	0	(106)
Recoveries	252	324	804	1,600
Ending Allowance	26,217	34,190	26,217	34,190
Provisions & Transfers	(3,027)	(1,242)	(5,565)	(12,490)
Consumer loans \| Land - consumer lot loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	5,105	3,292	4,939	2,729
Charge-offs	0	0	(27)	0
Recoveries	2	7	47	21
Ending Allowance	5,220	3,711	5,220	3,711
Provisions & Transfers	113	412	261	961
Consumer loans \| HELOC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	2,475	2,226	2,390	2,571
Charge-offs	0	0	0	0
Recoveries	249	51	350	51
Ending Allowance	2,632	2,213	2,632	2,213
Provisions & Transfers	(92)	(64)	(108)	(409)
Consumer loans \| Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Allowance	2,243	3,335	2,711	2,991
Charge-offs	(253)	(36)	(368)	(270)
Recoveries	331	289	726	805
Ending Allowance	2,697	3,629	2,697	3,629
Provisions & Transfers	$ 376	$ 41	$ (372)	$ 103

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

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+ References

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- Definition

Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (e)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

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- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

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- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

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- Definition

Financing Receivable, Allowance For Credit Losses, Provisions and Transfers

+ References

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