Covered Assets - Credit Risk Profile by Internally Assigned Grade by Loan Status Designation (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Covered Assets, Loan Status Designation [Line Items]
Total covered loans	$ 159,018	$ 213,203
Discount	(21,013)	(34,483)
Allowance	0wfsl_CoveredLoansAllowanceForLosses	(2,244)wfsl_CoveredLoansAllowanceForLosses
Covered loans, net	138,005	176,476
Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	59,853	100,161
Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	99,165	113,042
Single-Family Residential [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	20,750	23,067
Construction - Speculative [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Construction - Custom [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Land - Acquisition & Development [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	349	1,364
Land - Consumer Lot Loans [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	72	73
Multi-Family [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	903	6,598
Commercial Real Estate [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	22,967	51,336
Commercial & Industrial [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	4,383	5,492
HELOC [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	10,093	11,777
Consumer [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	336	454
Pool 1 - Construction and Land, Acquisition and Development [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	16,063	20,261
Pool 2 - Single-Family Residential [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	14,928	15,964
Pool 3 - Multi-family [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	458	523
Pool 4 - Home Equity Line of Credit and Other Consumer Loans [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	3,309	3,977
Pool 5 - Commercial Real Estate [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	59,068	64,391
Pool 6 - Commercial and Industrial [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	5,339	7,926
Pass [Member]
Covered Assets, Loan Status Designation [Line Items]
Total grade as a % of total net loans	97.60%	97.20%
Pass [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	48,157	70,926
Total grade as a % of total net loans	80.50%	70.80%
Pass [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	59,964	64,208
Pass [Member] \| Single-Family Residential [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	19,975	21,311
Pass [Member] \| Construction - Speculative [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Pass [Member] \| Construction - Custom [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Pass [Member] \| Land - Acquisition & Development [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	349	972
Pass [Member] \| Land - Consumer Lot Loans [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	72	73
Pass [Member] \| Multi-Family [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	903	6,598
Pass [Member] \| Commercial Real Estate [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	14,188	26,940
Pass [Member] \| Commercial & Industrial [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	2,241	2,801
Pass [Member] \| HELOC [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	10,093	11,777
Pass [Member] \| Consumer [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	336	454
Pass [Member] \| Pool 1 - Construction and Land, Acquisition and Development [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	6,639	8,349
Pass [Member] \| Pool 2 - Single-Family Residential [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	14,700	15,585
Pass [Member] \| Pool 3 - Multi-family [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	49	52
Pass [Member] \| Pool 4 - Home Equity Line of Credit and Other Consumer Loans [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	2,728	2,804
Pass [Member] \| Pool 5 - Commercial Real Estate [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	32,425	33,909
Pass [Member] \| Pool 6 - Commercial and Industrial [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	3,423	3,509
Special Mention [Member]
Covered Assets, Loan Status Designation [Line Items]
Total grade as a % of total net loans	0.20%	0.40%
Special Mention [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	115
Total grade as a % of total net loans	0.00%	0.10%
Special Mention [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	685	700
Special Mention [Member] \| Single-Family Residential [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Construction - Speculative [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Construction - Custom [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Land - Acquisition & Development [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Land - Consumer Lot Loans [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Multi-Family [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Commercial Real Estate [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	115
Special Mention [Member] \| Commercial & Industrial [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| HELOC [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Consumer [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Pool 1 - Construction and Land, Acquisition and Development [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Pool 2 - Single-Family Residential [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Pool 3 - Multi-family [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Pool 4 - Home Equity Line of Credit and Other Consumer Loans [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Special Mention [Member] \| Pool 5 - Commercial Real Estate [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	685	700
Special Mention [Member] \| Pool 6 - Commercial and Industrial [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member]
Covered Assets, Loan Status Designation [Line Items]
Total grade as a % of total net loans	2.10%	2.40%
Substandard [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	11,696	29,120
Total grade as a % of total net loans	19.50%	29.10%
Substandard [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	36,782	47,609
Substandard [Member] \| Single-Family Residential [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	775	1,756
Substandard [Member] \| Construction - Speculative [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member] \| Construction - Custom [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member] \| Land - Acquisition & Development [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	392
Substandard [Member] \| Land - Consumer Lot Loans [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member] \| Multi-Family [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member] \| Commercial Real Estate [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	8,779	24,281
Substandard [Member] \| Commercial & Industrial [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	2,142	2,691
Substandard [Member] \| HELOC [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member] \| Consumer [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Substandard [Member] \| Pool 1 - Construction and Land, Acquisition and Development [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	9,424	11,912
Substandard [Member] \| Pool 2 - Single-Family Residential [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	228	379
Substandard [Member] \| Pool 3 - Multi-family [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	409	471
Substandard [Member] \| Pool 4 - Home Equity Line of Credit and Other Consumer Loans [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	581	1,173
Substandard [Member] \| Pool 5 - Commercial Real Estate [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	24,224	29,782
Substandard [Member] \| Pool 6 - Commercial and Industrial [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	1,916	3,892
Doubtful [Member]
Covered Assets, Loan Status Designation [Line Items]
Total grade as a % of total net loans	0.10%	0.00%
Doubtful [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Total grade as a % of total net loans	0.00%	0.00%
Doubtful [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	1,734	525
Doubtful [Member] \| Single-Family Residential [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Construction - Speculative [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Construction - Custom [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Land - Acquisition & Development [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Land - Consumer Lot Loans [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Multi-Family [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Commercial Real Estate [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Commercial & Industrial [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| HELOC [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Consumer [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Pool 1 - Construction and Land, Acquisition and Development [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Pool 2 - Single-Family Residential [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Pool 3 - Multi-family [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Pool 4 - Home Equity Line of Credit and Other Consumer Loans [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Doubtful [Member] \| Pool 5 - Commercial Real Estate [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	1,734	0
Doubtful [Member] \| Pool 6 - Commercial and Industrial [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	525
Loss [Member]
Covered Assets, Loan Status Designation [Line Items]
Total grade as a % of total net loans	0.00%	0.00%
Loss [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Total grade as a % of total net loans	0.00%	0.00%
Loss [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Single-Family Residential [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Construction - Speculative [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Construction - Custom [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Land - Acquisition & Development [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Land - Consumer Lot Loans [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Multi-Family [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Commercial Real Estate [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Commercial & Industrial [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| HELOC [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Consumer [Member] \| Acquired Non Impaired Assets [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Pool 1 - Construction and Land, Acquisition and Development [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Pool 2 - Single-Family Residential [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Pool 3 - Multi-family [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Pool 4 - Home Equity Line of Credit and Other Consumer Loans [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Pool 5 - Commercial Real Estate [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	0	0
Loss [Member] \| Pool 6 - Commercial and Industrial [Member] \| Acquired Impaired Loans [Member]
Covered Assets, Loan Status Designation [Line Items]
Outstanding principal balance of acquired loans	$ 0	$ 0

Covered Assets - Credit Risk Profile by Internally Assigned Grade by Loan Status Designation (Details) (USD $)
In Thousands, unless otherwise specified