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Allowance for Losses on Loans - Impaired Loans Based on Loan Types (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 243,976	$ 251,274
Unpaid Principal Balance	255,925	289,340
Related Allowance	4,047	4,156
Average Recorded Investment	247,625	274,530
Amount of related allowance included in specific reserves	635	126
Amount of related allowance included in general reserves	3,412	4,030
Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	44,801	43,897
Unpaid Principal Balance	51,970	75,267
Related Allowance	0	0
Average Recorded Investment	44,349	40,392
Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	199,175	207,377
Unpaid Principal Balance	203,955	214,073
Related Allowance	4,047	4,156
Average Recorded Investment	203,276	234,138
Single-family residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	191,082	203,266
Unpaid Principal Balance	196,022	210,047
Related Allowance	3,412	4,030
Average Recorded Investment	197,172	224,094
Single-family residential | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	20,405	21,325
Unpaid Principal Balance	21,860	23,880
Related Allowance	0	0
Average Recorded Investment	20,864	19,371
Single-family residential | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	170,677	181,941
Unpaid Principal Balance	174,162	186,167
Related Allowance	3,412	4,030
Average Recorded Investment	176,308	204,723
Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment	969
Unpaid Principal Balance	969
Related Allowance	0
Average Recorded Investment	485
Construction | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	969
Unpaid Principal Balance	969
Related Allowance	0
Average Recorded Investment	485
Construction, custom
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	148
Unpaid Principal Balance	0	165
Related Allowance	0	0
Average Recorded Investment	74	231
Construction, custom | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	148
Unpaid Principal Balance	0	165
Related Allowance	0	0
Average Recorded Investment	74	231
Land - acquisition & development
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,376	420
Unpaid Principal Balance	1,405	8,298
Related Allowance	0	1
Average Recorded Investment	898	752
Land - acquisition & development | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,376	330
Unpaid Principal Balance	1,405	8,208
Related Allowance	0	0
Average Recorded Investment	853	176
Land - acquisition & development | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	90
Unpaid Principal Balance	0	90
Related Allowance	0	1
Average Recorded Investment	45	576
Land - consumer lot loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	7,705	8,157
Unpaid Principal Balance	8,151	8,856
Related Allowance	0	0
Average Recorded Investment	7,931	9,407
Land - consumer lot loans | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	300	208
Unpaid Principal Balance	375	330
Related Allowance	0	0
Average Recorded Investment	254	431
Land - consumer lot loans | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	7,405	7,949
Unpaid Principal Balance	7,776	8,526
Related Allowance	0	0
Average Recorded Investment	7,677	8,976
Multi-family
Financing Receivable, Impaired [Line Items]
Recorded Investment	730	632
Unpaid Principal Balance	734	3,724
Related Allowance	5	5
Average Recorded Investment	682	1,772
Multi-family | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	250	139
Unpaid Principal Balance	254	3,231
Related Allowance	0	0
Average Recorded Investment	195	748
Multi-family | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	480	493
Unpaid Principal Balance	480	493
Related Allowance	5	5
Average Recorded Investment	487	1,024
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	28,282	27,969
Unpaid Principal Balance	34,475	39,194
Related Allowance	106	120
Average Recorded Investment	28,126	28,457
Commercial real estate | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	16,372	12,890
Unpaid Principal Balance	21,720	22,487
Related Allowance	0	0
Average Recorded Investment	14,631	11,466
Commercial real estate | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	11,910	15,079
Unpaid Principal Balance	12,755	16,707
Related Allowance	106	120
Average Recorded Investment	13,495	16,991
Commercial & industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment	11,695	8,279
Unpaid Principal Balance	11,762	14,321
Related Allowance	524	0
Average Recorded Investment	9,987	7,722
Commercial & industrial | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	4,439	8,279
Unpaid Principal Balance	4,506	14,321
Related Allowance	0	0
Average Recorded Investment	6,359	7,425
Commercial & industrial | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	7,256	0
Unpaid Principal Balance	7,256	0
Related Allowance	524	0
Average Recorded Investment	3,628	297
HELOC
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,976	2,218
Unpaid Principal Balance	2,182	3,018
Related Allowance	0	0
Average Recorded Investment	2,097	1,938
HELOC | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	620	490
Unpaid Principal Balance	747	1,212
Related Allowance	0	0
Average Recorded Investment	555	487
HELOC | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,356	1,728
Unpaid Principal Balance	1,435	1,806
Related Allowance	0	0
Average Recorded Investment	1,542	1,451
Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	161	185
Unpaid Principal Balance	225	1,717
Related Allowance	0	0
Average Recorded Investment	173	157
Consumer | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	70	88
Unpaid Principal Balance	134	1,433
Related Allowance	0	0
Average Recorded Investment	79	57
Consumer | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	91	97
Unpaid Principal Balance	91	284
Related Allowance	0	0
Average Recorded Investment	$ 94	$ 100

X

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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-Publisher FASB
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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-Section 50
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
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