Allowance for Losses on Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	$ 133,086	$ 127,576	$ 129,257	$ 123,073
Charge-offs	(4,752)	(3,674)	(7,408)	(4,865)
Recoveries	5,688	3,764	10,923	9,408
Provision & Transfers	0	1,000	1,250	1,050
Ending Allowance	134,022	128,666	134,022	128,666
Single-family residential
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	31,476	34,144	33,033	36,892
Charge-offs	(65)	(299)	(238)	(1,049)
Recoveries	47	283	586	615
Provision & Transfers	56	273	(1,867)	(2,057)
Ending Allowance	31,514	34,401	31,514	34,401
Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	33,396	27,389	31,317	24,556
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision & Transfers	661	2,744	2,740	5,577
Ending Allowance	34,057	30,133	34,057	30,133
Construction - custom
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,976	2,081	1,842	1,944
Charge-offs	(339)	0	(339)	(50)
Recoveries	0	0	0	0
Provision & Transfers	247	(67)	381	120
Ending Allowance	1,884	2,014	1,884	2,014
Land - acquisition & development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	9,734	7,622	7,978	6,829
Charge-offs	(65)	(12)	(65)	(12)
Recoveries	2,025	2,699	5,107	7,278
Provision & Transfers	(2,306)	(2,609)	(3,632)	(6,395)
Ending Allowance	9,388	7,700	9,388	7,700
Land - consumer lot loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	2,076	2,853	2,164	2,649
Charge-offs	(215)	(1)	(336)	(67)
Recoveries	0	35	265	35
Provision & Transfers	171	20	(61)	290
Ending Allowance	2,032	2,907	2,032	2,907
Multi-family
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	7,394	7,982	8,329	7,862
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision & Transfers	(111)	109	(1,046)	229
Ending Allowance	7,283	8,091	7,283	8,091
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	12,448	11,588	11,852	11,818
Charge-offs	0	0	(339)	(36)
Recoveries	90	91	860	92
Provision & Transfers	466	(100)	631	(295)
Ending Allowance	13,004	11,579	13,004	11,579
Commercial & industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	30,574	29,330	28,702	28,524
Charge-offs	(4,034)	(3,317)	(4,499)	(3,433)
Recoveries	3,218	433	3,276	603
Provision & Transfers	1,313	1,069	3,592	1,821
Ending Allowance	31,071	27,515	31,071	27,515
HELOC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,082	802	781	855
Charge-offs	0	0	(1,086)	(1)
Recoveries	1	0	45	0
Provision & Transfers	4	9	1,347	(43)
Ending Allowance	1,087	811	1,087	811
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	2,930	3,785	3,259	1,144
Charge-offs	(34)	(45)	(506)	(217)
Recoveries	307	223	784	785
Provision & Transfers	(501)	(448)	(835)	1,803
Ending Allowance	$ 2,702	$ 3,515	$ 2,702	$ 3,515

A valuation allowance for financing receivables that are expected to be uncollectible.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Financing Receivable, Allowance for Credit Losses, Provision and Transfers

+ References

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