Allowance for Losses on Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	$ 123,073	$ 113,494
Charge-offs	(752)	(404)
Recoveries	3,834	5,700
Provision & Transfers	1,000	(334)
Ending Allowance	127,155	118,456
Single-family residential
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	36,892	37,796
Charge-offs	(461)	(115)
Recoveries	121	151
Provision & Transfers	(624)	374
Ending Allowance	35,928	38,206
Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	24,556	19,838
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	658	2,096
Ending Allowance	25,214	21,934
Construction - custom
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,944	1,080
Charge-offs	(50)	0
Recoveries	0	0
Provision & Transfers	158	30
Ending Allowance	2,052	1,110
Land - acquisition & development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	6,829	6,023
Charge-offs	0	(20)
Recoveries	3,372	4,018
Provision & Transfers	(2,846)	(3,356)
Ending Allowance	7,355	6,665
Land - consumer lot loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	2,649	2,535
Charge-offs	(47)	(17)
Recoveries	0	70
Provision & Transfers	304	(87)
Ending Allowance	2,906	2,501
Multi-family
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	7,862	6,925
Charge-offs	0	0
Recoveries	0	0
Provision & Transfers	42	704
Ending Allowance	7,904	7,629
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	11,818	8,588
Charge-offs	0	(11)
Recoveries	0	356
Provision & Transfers	(193)	1,235
Ending Allowance	11,625	10,168
Commercial & industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	28,524	28,008
Charge-offs	(116)	(58)
Recoveries	55	725
Provision & Transfers	805	(939)
Ending Allowance	29,268	27,736
HELOC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	855	813
Charge-offs	0	(37)
Recoveries	0	1
Provision & Transfers	(47)	55
Ending Allowance	808	832
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,144	1,888
Charge-offs	(78)	(146)
Recoveries	286	379
Provision & Transfers	2,743	(446)
Ending Allowance	$ 4,095	$ 1,675

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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

No definition available.

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