Allowance for Losses on Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	$ 129,257	$ 123,073
Charge-offs	(1,641)	(752)
Recoveries	3,049	3,834
Provision & Transfers	500	1,000
Ending Allowance	131,165	127,155
Single-family residential
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	33,033	36,892
Charge-offs	(25)	(461)
Recoveries	230	121
Provision & Transfers	(1,754)	(624)
Ending Allowance	31,484	35,928
Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	31,317	24,556
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	146	658
Ending Allowance	31,463	25,214
Construction - custom
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,842	1,944
Charge-offs	0	(50)
Recoveries	0	0
Provision & Transfers	84	158
Ending Allowance	1,926	2,052
Land - acquisition & development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	7,978	6,829
Charge-offs	0	0
Recoveries	1,782	3,372
Provision & Transfers	(604)	(2,846)
Ending Allowance	9,156	7,355
Land - consumer lot loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	2,164	2,649
Charge-offs	(72)	(47)
Recoveries	265	0
Provision & Transfers	(213)	304
Ending Allowance	2,144	2,906
Multi-family
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	8,329	7,862
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	(445)	42
Ending Allowance	7,884	7,904
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	11,852	11,818
Charge-offs	(339)	0
Recoveries	525	0
Provision & Transfers	673	(193)
Ending Allowance	12,711	11,625
Commercial & industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	28,702	28,524
Charge-offs	(179)	(116)
Recoveries	33	55
Provision & Transfers	1,723	805
Ending Allowance	30,279	29,268
HELOC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	781	855
Charge-offs	(886)	0
Recoveries	1	0
Provision & Transfers	1,168	(47)
Ending Allowance	1,064	808
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	3,259	1,144
Charge-offs	(140)	(78)
Recoveries	213	286
Provision & Transfers	(278)	2,743
Ending Allowance	$ 3,054	$ 4,095

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

No definition available.

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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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