Westbury Bancorp (WBBW) 10-Q 30 Apr 15 2015 Q2 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	6 Months Ended
	Mar. 31, 2015	Apr. 29, 2015
Document and Entity Information
Entity Registrant Name	Westbury Bancorp, Inc.
Entity Central Index Key	1553326
Document Type	10-Q
Document Period End Date	31-Mar-15
Amendment Flag	FALSE
Current Fiscal Year End Date	-21
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		4,514,949
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Assets
Cash and due from banks	$10,427	$9,369
Interest-bearing deposits	6,378	8,239
Cash and cash equivalents	16,805	17,608
Securities available-for-sale	77,881	90,346
Securities held to maturity, at amortized cost ($3,042 fair value at March 31, 2015)	3,025	0
Loans held for sale, at lower of cost or fair value	1,594	326
Loans, net of allowance for loan losses of $4,483 and $4,072 at March 31 and September 30, respectively	467,447	416,874
Federal Home Loan Bank stock, at cost	3,350	2,670
Foreclosed real estate	2,100	2,355
Real estate held for investment	3,697	3,763
Office properties and equipment, net	11,337	11,181
Cash surrender value of bank-owned life insurance	12,972	12,742
Mortgage servicing rights	1,409	1,624
Deferred tax asset	4,899	5,702
Other assets	3,618	3,504
Total assets	610,134	568,695
Liabilities
Deposits	512,047	454,928
Advances from Federal Home Loan Bank	13,000	17,000
Advance payments by borrowers for property taxes and insurance	1,966	5,869
Other liabilities	3,985	4,411
Total liabilities	530,998	482,208
Stockholders’ Equity
Preferred stock $0.01 par value, 50,000,000 shares authorized; none issued or outstanding	0	0
Common stock $0.01 par value, 100,000,000 shares authorized; 5,346,206 shares issued at March 31, 2015 and September 30, 2014	53	53
Additional paid-in capital	49,661	49,164
Retained earnings	46,121	45,190
Unearned Employee Stock Ownership Plan (ESOP) shares	-3,651	-3,754
Accumulated other comprehensive income (loss)	441	-46
Less common stock repurchased, 818,157 shares at cost, at March 31, 2015 and 271,296 at September 30, 2014	-13,489	-4,120
Total stockholders’ equity	79,136	86,487
Total liabilities and stockholders’ equity	$610,134	$568,695

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Securities held to maturity, fair value	$3,042
Allowance for loan losses	$4,483	$4,072
Preferred stock, par value (in dollars per share)	$0.01	$0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	5,346,206	5,346,206
Treasury stock, shares	818,157	271,296

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Interest and dividend income:
Loans	$4,685	$3,949	$9,144	$7,927
Investments - nontaxable	15	22	32	38
Investments - taxable	404	472	796	967
Interest bearing deposits	16	29	28	66
Total interest and dividend income	5,120	4,472	10,000	8,998
Interest expense:
Deposits	446	398	871	822
Advances from the Federal Home Loan Bank	14	1	18	1
Total interest expense	460	399	889	823
Net interest income before provision for loan losses	4,660	4,073	9,111	8,175
Provision for loan losses	300	200	650	350
Net interest income after provision for loan losses	4,360	3,873	8,461	7,825
Noninterest income:
Service fees on deposit accounts	999	966	2,155	2,031
Gain on sales of loans, net	174	17	243	64
Servicing fee income, net of amortization and impairment	6	71	43	318
Insurance and securities sales commissions	98	99	156	194
Gain on sales of securities	3	24	73	24
Gain (loss) on sales of branches and other assets	-12	-68	6	-68
Increase in cash surrender value of life insurance	128	83	230	188
Rental income from real estate operations	148	157	276	317
Other income	67	78	103	117
Total noninterest income	1,611	1,427	3,285	3,185
Noninterest expenses:
Salaries and employee benefits	2,439	2,429	4,820	4,726
Commissions	71	48	126	99
Occupancy	385	497	698	924
Furniture and equipment	125	129	228	259
Data processing	792	853	1,573	1,714
Advertising	44	25	104	92
Real estate held for investment	120	159	223	311
Net loss from operations and sale of foreclosed real estate	31	116	179	450
FDIC insurance premiums	107	169	212	342
Valuation loss on real estate held for sale	0	1,964	0	1,964
Branch realignment	0	573	0	573
Other expenses	1,108	1,352	2,164	2,504
Total noninterest expenses	5,222	8,314	10,327	13,958
Income before income tax expense (benefit)	749	-3,014	1,419	-2,948
Income tax expense (benefit)	265	-1,215	488	-1,217
Net income (loss)	$484	($1,799)	$931	($1,731)
Earnings per share:
Basic (in dollars per share)	$0.11	($0.38)	$0.21	($0.36)
Diluted (in dollars per share)	$0.11	($0.38)	$0.21	($0.36)

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Loss) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$484	($1,799)	$931	($1,731)
Other comprehensive income, before tax:
Unrealized gains on available-for-sale securities	620	1,108	875	612
Reclassification adjustment for realized gains included in net income	-3	-24	-73	-24
Other comprehensive income, before tax	617	1,084	802	588
Income tax expense related to items of other comprehensive income	-242	-459	-315	-218
Other comprehensive income, net of tax	375	625	487	370
Comprehensive income (loss)	$859	($1,174)	$1,418	($1,361)

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Stockholders' Equity (USD $)	Total	Preferred Stock	Common Stock	Additional Paid In Capital	Retained Earnings	Unearned ESOP Shares	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
In Thousands, unless otherwise specified
Balance at Sep. 30, 2013	$90,602	$0	$51	$48,800	$46,625	($4,114)	($760)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	-1,731	0			-1,731
Other comprehensive income (loss), net of tax	370						370
Allocation of 5,142 shares by ESOP	287			81		206
Commitment to be allocated of 5,142 ESOP shares	72			21		51
Balance at Mar. 31, 2014	89,600	0	51	48,902	44,894	-3,857	-390	0
Balance at Sep. 30, 2014	86,487	0	53	49,164	45,190	-3,754	-46	-4,120
Increase (Decrease) in Stockholders' Equity
Net income (loss)	931	0			931
Other comprehensive income (loss), net of tax	487						487
Repurchase of 546,861 shares of common stock	-9,369							-9,369
Stock based compensation expense	402			402
Allocation of 5,142 shares by ESOP	112	0		61		51
Commitment to be allocated of 5,142 ESOP shares	86			34		52
Balance at Mar. 31, 2015	$79,136	$0	$53	$49,661	$46,121	($3,651)	$441	($13,489)

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical)	6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Stockholders' Equity [Abstract]
Number of shares purchased by ESOP	0	0
Number of shares repurchased during period	546,861	0
Number of restricted shares issued during period	0	0
Number of shares allocated by ESOP	5,142	20,570
Number of shares committed to be allocated by ESOP	5,142	5,142

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash Flows From Operating Activities
Net income (loss)	$931	($1,731)
Adjustments to reconcile net income to net cash used in operating activities:
Provision for loan losses	650	350
Depreciation and amortization	317	393
Depreciation on real estate held for investment	66	89
Net amortization of securities premiums and discounts	272	326
Amortization and impairment of mortgage servicing rights	215	-14
Capitalization of mortgage servicing rights	0	-1
Gain on sales of available-for-sale securities	-73	-24
(Gain) loss on sales of branches and other assets	-6	68
Write-down of real estate held-for-sale	0	1,964
Branch realignment	0	573
Loss on sale of foreclosed real estate	20	150
Write-down of foreclosed real estate	57	183
Loans originated for sale	-14,510	-5,188
Proceeds from sale of loans	13,485	5,783
Gain on sale of loans, net	-243	-64
ESOP compensation expense	198	168
Stock based compensation expense	402	0
Deferred income taxes	488	-1,191
Increase in cash surrender value of life insurance	-230	-188
Net change in:
Other assets	-107	-312
Other liabilities and advance payments by borrowers for property taxes and insurance	-4,317	-5,380
Net cash used in operating activities	-2,385	-4,046
Cash Flows From Investing Activities
Purchases of securities available-for-sale	-10,287	-9,599
Proceeds from sales of securities available-for-sale	17,536	14,145
Proceeds from maturities, prepayments, and calls of securities available-for-sale	5,819	5,038
Purchases of securities held to maturity	-3,025	0
Purchase of FHLB stock	-680	0
Net increase in loans	-51,648	-14,924
Purchases of office properties and equipment	-486	-483
Proceeds from sales of foreclosed real estate	603	717
Net cash used in investing activities	-42,168	-5,106
Cash Flows From Financing Activities
Net increase in deposits	57,119	10,400
Decrease in Federal Home Loan Bank borrowings	-4,000	0
Purchase of Company treasury stock	-9,369	0
Net cash provided by financing activities	43,750	10,400
Net increase (decrease) in cash and cash equivalents	-803	1,248
Cash and cash equivalents at beginning	17,608	47,665
Cash and cash equivalents at end	16,805	48,913
Supplemental Disclosures of Cash Flow Information
Interest paid (including amounts credited to deposits)	888	822
Supplemental Schedules of Non-cash Investing Activities
Loans receivable transferred to foreclosed real estate	$425	$474

Basis_of_Presentation

Basis of Presentation	6 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation
	The accompanying unaudited consolidated financial statements of Westbury Bancorp, Inc. and its wholly-owned subsidiary, Westbury Bank, (the "Bank", and collectively, the “Company”) have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Rule 8-03 of Regulation S-X.  Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations.
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period.  Estimates used in the preparation of the financial statements are based on various factors including the current interest rate environment and the general strength of the local economy.  Changes in the overall interest rate environment can significantly affect the Company’s net interest income and the value of its recorded assets and liabilities.  Actual results could differ from those estimates used in the preparation of the financial statements.  Certain prior period amounts have been reclassified to conform to current period presentation.  These reclassifications did not result in any changes to previously reported net income or stockholders’ equity.
	In the opinion of management, the accompanying unaudited financial statements contain all adjustments (consisting only of normal recurring accruals) necessary to present fairly the Company’s financial condition as of March 31, 2015 and September 30, 2014 and the results of operations and cash flows for the interim periods ended March 31, 2015 and 2014.  All interim amounts are unaudited, and the results of operations for the interim periods herein are not necessarily indicative of the results of operations to be expected for the year.  These financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended September 30, 2014 filed as part of Westbury Bancorp, Inc.’s Annual Report on Form 10-K for the year ended September 30, 2014.
	The Jumpstart Our Business Startups Act (the JOBS Act), which was signed into law on April 5, 2012, has made numerous changes to the federal securities laws to facilitate access to capital markets. Under the JOBS Act, a company with total annual gross revenues of less than $1.0 billion during its most recently completed fiscal year qualifies as an “emerging growth company.” The Company qualifies as an “emerging growth company” and believes that it will continue to qualify as an “emerging growth company” until five years from the completion of the stock offering.
	As an “emerging growth company,” the Company has elected to use the extended transition period to delay adoption of new or revised accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. Accordingly, the financial statements may not be comparable to the financial statements of companies that comply with such new or revised accounting standards.

Recent_Accounting_Developments

Recent Accounting Developments	6 Months Ended
	Mar. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Developments	Recent Accounting Developments
	In January 2014, the FASB issued ASU 2014-04, Receivables (Topic 310) - Troubled Debt Restructurings by Creditors. ASU 2014-04 is intended to reduce diversity by clarifying when an in substance repossession or foreclosure occurs, that is, when a creditor should be considered to have received physical possession of residential real property collateralizing a consumer mortgage loan such that the loan receivable should be derecognized and the real estate property recognized. ASU 2014-04 is effective for annual periods and interim periods within those annual periods beginning after December 15, 2014. Adoption by the Company is not expected to have a material impact on the consolidated financial statements and related disclosures.
	In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). ASU 2014-09 is intended to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. GAAP. ASU 2014-09 is effective for annual reporting periods and interim periods within those annual periods beginning after December 15, 2017. Adoption by the Company is not expected to have a material impact on the consolidated financial statements and related disclosures.
	In June 2014, the FASB issued ASU 2014-11, Transfers and Servicing (Topic 860) - Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures. ASU 2014-11 is intended to clarify the accounting for and improve the disclosures related to repurchase-to-maturity transactions and repurchase financings. ASU 2014-11 is effective for the first interim or annual period beginning after December 15, 2015. Adoption by the Company is not expected to have a material impact on the consolidated financial statements and related disclosures.
	In June 2014, the FASB issued ASU 2014-12, Compensation - Stock Compensation (Topic 718) - Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved After the Requisite Service Period. ASU 2014-12 is intended to clarify the accounting for the timing of expense recognition related to employee share-based payments in which a performance target that effects vesting could be achieved after the requisite service period. ASU 2014-12 is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. Adoption by the Company is not expected to have a material impact on the consolidated financial statements and related disclosures.
	In August 2014, the FASB issued ASU 2014-14, Receivables - Troubled Debt Restructuring by Creditors (Topic 310) - Classification of Certain Government-Guaranteed Mortgage Loans Upon Foreclosure. ASU 2014-14 is intended to clarify the accounting for and improve the consistency of balance sheet classification of certain foreclosed mortgage loans that are either fully or partially guaranteed under government programs. Greater consistency in classification of such mortgage loans upon foreclosure is expected to provide more decision-useful information about a creditor's foreclosed mortgage loans that are expected to be recovered, at least in part, through government guarantees. ASU 2014-14 is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. Adoption by the Company is not expected to have a material impact on the consolidated financial statements and related disclosures.

Earnings_Per_Share

Earnings Per Share	6 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share
	Earnings per common share is computed using the two-class method. Basic earnings per common share is computed by dividing net income by the weighted-average number of common shares outstanding, adjusted for weighted average unallocated ESOP shares, during the applicable period, excluding outstanding participating securities. Participating securities include non-vested restricted stock awards to the extent holders of these securities receive non-forfeitable dividends or dividend equivalents at the same rate as holders of the Company's common stock. Diluted earnings per share is computed using the weighted-average number of shares determined for the basic earnings per common share computation plus the dilutive effect of stock compensation using the treasury stock method.
	The following table presents a reconciliation of the number of shares used in the calculation of basic and diluted earnings per common share (in thousands, except share and per share data).
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Net income (loss)	$	484		$	(1,799	)	$	931		$	(1,731	)
	Basic potential common shares:
	Weighted average shares outstanding	4,657,638			5,142,541			4,746,438			5,142,541
	Weighted average unallocated ESOP shares	(368,549		)	(387,405		)	(371,149		)	(390,262		)
	Basic weighted average shares outstanding	4,289,089			4,755.14			4,375,289			4,752.28
	Dilutive effect of equity awards	33,670			—			28,971			—
	Diluted weighted average shares outstanding	4,322,759			4,755,136			4,404,260			4,752,279
	Basic income (loss) per share	$	0.11		$	(0.38	)	$	0.21		$	(0.36	)
	Diluted income (loss) per share	$	0.11		$	(0.38	)	$	0.21		$	(0.36	)

Investment_Securitites

Investment Securitites	6 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities
	The amortized cost and fair value of investment securities are summarized as follows:
		31-Mar-15
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			(Losses)
	Available for Sale
	U.S. Government and agency securities	$	24	$	1		$	—		$	25
	U.S. Government agency residential mortgage-backed securities	38,762		534			(112		)	39,184
	U.S. Government agency collateralized mortgage obligations	2,424		23			(47		)	2,400
	U.S. Government agency commercial mortgage-backed securities	9,617		77			—			9,694
	Municipal securities	26,328		278			(28		)	26,578
	Total Available for Sale	77,155		913			(187		)	77,881
	Held to Maturity
	Municipal securities	3,025		17			—			3,042
	Total Investment Securities	$	80,180	$	930		$	(187	)	$	80,923
		30-Sep-14
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			(Losses)
	Available for Sale
	U.S. Government and agency securities	$	5,250	$	—		$	(71	)	$	5,179
	U.S. Government agency residential mortgage-backed securities	37,144		389			(337		)	37,196
	U.S. Government agency collateralized mortgage obligations	3,458		30			(56		)	3,432
	U.S. Government agency commercial mortgage-backed securities	10,835		11			(94		)	10,752
	Municipal securities	33,735		280			(228		)	33,787
	Total Available for Sale	90,422		710			(786		)	90,346
	Held to Maturity
	Municipal securities	—		—			—			—
	Total Investment Securities	$	90,422	$	710		$	(786	)	$	90,346
	The amortized cost and fair value of investment securities, by contractual maturity at March 31, 2015 are shown in the following table.  Actual maturities differ from contractual maturities for mortgage-backed securities because the mortgages underlying the securities may be called or repaid without penalty.  Therefore, these securities are not presented in the maturity categories in the table below.
		31-Mar-15
		Amortized Cost		Fair Value
	Available for sale:
	Due in one year or less	$	2,447	$	2,475
	Due after one year through five years	14,696		14,865
	Due after five years through ten years	7,604		7,671
	Due after ten years	1,605		1,592
	U.S. Government agency collateralized mortgage obligations	2,424		2,400
	U.S. Government agency residential mortgage-backed securities	38,762		39,184
	U.S. Government agency commercial mortgage-backed securities	9,617		9,694
		77,155		77,881
	Held to maturity:
	Due in one year or less	566		566
	Due after one year through five years	679		680
	Due after five years through ten years	929		937
	Due after ten years	851		859
		3,025		3,042
	Total	$	80,180	$	80,923
	Proceeds from sales of investment securities during the three months ended March 31, 2015 and 2014, were $5,452 and $14,145, respectively. Gross realized gains, during the three months ended March 31, 2015 and 2014, on these sales amount to $14 and $170, respectively. Gross realized losses on these sales were $11 and $146, during the three months ended March 31, 2015 and 2014 respectively.
	Proceeds from sales of investment securities during the six months ended March 31, 2015 and 2014, were $17,536 and $14,145, respectively. Gross realized gains, during the six months ended March 31, 2015 and 2014, on these sales amounted to $125 and $170, respectively. Gross realized losses on these sales were $52 and $146, during the six months ended March 31, 2015 and 2014, respectively.
	There were no securities that were pledged to secure treasury, tax, and loan deposits and other purposes required or permitted by law at March 31, 2015 and September 30, 2014.
	Information pertaining to securities with gross unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, are summarized as follows:
		31-Mar-15
		Less than 12 Months					12 Months or Longer						Total
		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
		Value		Loss			Value			Loss			Value		Loss
	U.S. Government and agency securities	$	—	$	—		$	—		$	—		$	—	$	—
	U.S. Government agency residential mortgage-backed securities	3,858		(13		)	8,321			(99		)	12,179		(112		)
	U.S. Government agency collateralized mortgage obligations	—		—			753			(47		)	753		(47		)
	U.S Government agency commercial mortgage-backed securities	—		—			—			—			—		—
	Municipal securities	2,008		(13		)	1,690			(15		)	3,698		(28		)
		$	5,866	$	(26	)	$	10,764		$	(161	)	$	16,630	$	(187	)
		30-Sep-14
	Less than 12 Months					12 Months or Longer						Total
	Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
	Value		Loss			Value			Loss			Value		Loss
U.S. Government and agency securities	$	—	$	—		$	5,179		$	(71	)	$	5,179	$	(71	)
U.S. Government agency residential mortgage-backed securities	9,617		(54		)	13,075			(283		)	22,692		(337		)
U.S. Government agency collateralized mortgage obligations	—		—			891			(56		)	891		(56		)
U.S. Government agency commercial mortgage-backed securities	6,235		(73		)	1,033			(21		)	7,268		(94		)
Municipal securities	3,046		(8		)	13,621			(220		)	16,667		(228		)
	$	18,898	$	(135	)	$	33,799		$	(651	)	$	52,697	$	(786	)
At March 31, 2015, the investment portfolio included 17 securities available-for-sale which had been in an unrealized loss position for more than twelve months and 8 securities available-for-sale which had been in an unrealized loss position for less than twelve months. These securities are considered to be acceptable credit risks.  Based upon an evaluation of the available evidence, including recent changes in market rates, credit rating information and information obtained from regulatory filings, management believes the decline in fair value for these securities is temporary.  The Company does not have any current requirement to sell and does not intend to sell these securities prior to any anticipated recovery in fair value.
At September 30, 2014, the investment portfolio included 63 securities available-for-sale which had been in an unrealized loss position for greater than twelve months and 25 securities available-for-sale which had been in an unrealized loss position for less than twelve months.

Loans

Loans	6 Months Ended
	Mar. 31, 2015
Loans and Leases Receivable Disclosure [Abstract]
Loans	Loans
	A summary of the balances of loans follows:
		March 31, 2015				September 30,
						2014
	Real estate:
	Single family	$	150,102			$	135,337
	Multifamily	92,194				76,396
	Commercial real estate	155,121				135,121
	Construction and land development	20,941				16,362
	Total real estate	418,358				363,216
	Commercial business	34,569				37,675
	Consumer:
	Home equity lines of credit	12,608				14,275
	Education	4,374				4,694
	Other	2,342				1,321
	Total consumer	19,324				20,290
	Total loans	472,251				421,181
	Less:
	Net deferred loan fees	321				235
	Allowance for loan losses	4,483				4,072
	Net loans	$	467,447			$	416,874
	The following tables present the contractual aging of the recorded investment in past due loans by class of loans as of March 31, 2015 and September 30, 2014:
	March 31, 2015		Current				30-59 Days			60-89 Days			Loans Past			Total
							Past Due			Past Due			Due 90 Days
													or More
	Single family		$	148,804			$	1,016		$	—		$	282		$	150,102
	Multifamily		92,194				—			—			—			92,194
	Commercial real estate		154,727				—			—			394			155,121
	Construction and land development		20,941				—			—			—			20,941
	Commercial business		34,567				2			—			—			34,569
	Consumer and other:
	Home equity lines of credit		12,428				—			—			180			12,608
	Education		4,180				54			66			74			4,374
	Other		2,342				—			—			—			2,342
			$	470,183			$	1,072		$	66		$	930		$	472,251
	September 30, 2014		Current				30-59 Days			60-89 Days			Loans Past			Total
							Past Due			Past Due			Due 90 Days
													or More
	Single family		$	133,102			$	1,623		$	162		$	450		$	135,337
	Multifamily		76,396				—			—			—			76,396
	Commercial real estate		134,584				178			163			196			135,121
	Construction and land development		16,362				—			—			—			16,362
	Commercial business		37,653				—			—			22			37,675
	Consumer and other:
	Home equity lines of credit		13,918				228			—			129			14,275
	Education		4,502				28			44			120			4,694
	Other		1,319				—			—			2			1,321
			$	417,836			$	2,057		$	369		$	919		$	421,181
	There were no loans past due ninety days or more still accruing interest as of March 31, 2015 and September 30, 2014.
	The following table presents the recorded investment in nonaccrual loans by class of loans as of March 31, 2015 and September 30, 2014:
		31-Mar-15				September 30,
						2014
	Single family	$	426			$	791
	Multifamily	—				—
	Commercial real estate	394				350
	Construction and land development	—				—
	Commercial business	—				22
	Consumer and other:
	Home equity lines of credit	194				145
	Education	74				120
	Other	—				2
		$	1,088			$	1,430
	As part of the on-going monitoring of the credit quality of the Company’s loan portfolio, management categorizes loans into risk categories based on relevant information about the ability of the borrowers to service their debt and comply with various terms of their loan agreements.  The Company considers current financial information, historical payment experience, credit documentation, public information and current economic trends.  Generally, all sizeable credits receive a financial review no less than annually to monitor and adjust, if necessary, the credit’s risk profile.  Credits classified as watch and special mention generally receive a review more frequently than annually.
	The Company categorizes loans into the following risk categories based on relevant information about the ability of borrowers to service their debt:
Pass — A pass asset is well protected by the current worth and paying capacity of the obligor (or guarantors, if any) or by the fair value, less costs to acquire and sell in a timely manner, of any underlying collateral.
Watch — A watch asset has potential weaknesses that deserve management’s close attention.  If left uncorrected, these potential weaknesses may result in deterioration of the repayment prospects for the asset or in the Company’s credit position at some future date.  Watch assets are not adversely classified and do not expose the Company to sufficient risk to warrant adverse classification.
Special Mention — A special mention asset has characteristics of deterioration in quality exhibited by any number of well-defined weaknesses requiring significant corrective action.  The repayment ability of the borrower has not been validated, or has become marginal or weak and the loan may have exhibited some overdue payments or payment extensions and/or renewals.
Substandard — A substandard asset is an asset with a well-defined weakness that jeopardizes repayment in whole or in part, of the debt.  These credits are inadequately protected by the current sound worth and paying capacity of the obligor or of the collateral pledged.  These assets are characterized by the distinct possibility that the Company will or has sustained some loss of principal and/or interest if the deficiencies are not corrected.
Doubtful — A doubtful asset is an asset that has all the weaknesses inherent in the substandard classification with the added characteristic that the weaknesses make collection or liquidation in full, on the basis of currently existing facts, conditions and values, highly questionable and improbable.  These credits have a high probability for loss, yet because certain important and reasonably specific pending factors may work toward the strengthening of the asset, its classification of loss is deferred until its more exact status can be determined.
Homogeneous loan types are assessed for credit quality based on the contractual aging status of the loan and payment activity.  In certain cases, based upon payment performance, the loan being related with another commercial type loan or for other reasons, a loan may be categorized into one of the risk categories noted above, unless such loan carries private mortgage insurance (PMI).  Such assessment is completed at the end of each reporting period.
The following tables present the risk category of loans evaluated by internal asset classification based on the most recent analysis performed and the contractual aging as of March 31, 2015 and September 30, 2014:
March 31, 2015		Pass				Watch			Special Mention			Substandard			Doubtful			Total
Single family		$	147,649			$	1,151		$	—		$	1,302		$	—		$	150,102
Multifamily		88,915				2,841			438			—			—			92,194
Commercial real estate		148,027				4,931			961			1,202			—			155,121
Construction and land development		20,941				—			—			—			—			20,941
Commercial business		31,284				3,147			—			138			—			34,569
Consumer and other:
Home equity lines of credit		12,343				—			—			265			—			12,608
Education		4,374				—			—			—			—			4,374
Other		2,342				—			—			—			—			2,342
Total		$	455,875			$	12,070		$	1,399		$	2,907		$	—		$	472,251
September 30, 2014		Pass				Watch			Special Mention			Substandard			Doubtful			Total
Single family		$	132,067			$	1,317		$	118		$	1,835		$	—		$	135,337
Multifamily		73,876				1,915			445			160			—			76,396
Commercial real estate		126,319				6,117			858			1,827			—			135,121
Construction and land development		16,357				—			—			5			—			16,362
Commercial business		34,112				3,459			—			104			—			37,675
Consumer and other:
Home equity lines of credit		14,088				—			—			187			—			14,275
Education		4,694				—			—			—			—			4,694
Other		1,319				—			—			2			—			1,321
		$	402,832			$	12,808		$	1,421		$	4,120		$	—		$	421,181
The following tables provide additional detail of the activity in the allowance for loan losses, by portfolio segment, for the three months ended March 31, 2015 and 2014:
Three Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
31-Mar-15									Real Estate			Land Development			Business			and Other
Allowance for loan losses:
Beginning balance		$	1,025			$	932		$	1,388		$	367		$	412		$	100		$	4,224
Provision for loan losses		86				93			124			(6		)	(2		)	5			300
Loans charged-off		(47		)		—			(14		)	—			—			—			(61		)
Recoveries		—				—			9			—			5			6			20
Ending balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
Period-ended amount allocated for:
Individually evaluated for impairment		$	40			$	—		$	—		$	—		$	—		$	57		$	97
Collectively evaluated for impairment		1,024				1,025			1,507			361			415			54			4,386
Ending Balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
Loans:
Individually evaluated for impairment		$	1,683			$	1,874		$	1,085		$	—		$	—		$	278		$	4,920
Collectively evaluated for impairment		148,419				90,320			154,036			20,941			34,569			19,046			467,331
Ending Balance		$	150,102			$	92,194		$	155,121		$	20,941		$	34,569		$	19,324		$	472,251
Three Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
31-Mar-14									Real Estate			Land Development			Business			and Other
Allowance for loan losses:
Beginning balance		$	1,658			$	138		$	1,493		$	171		$	220		$	63		$	3,743
Provision for loan losses		(183		)		(35		)	253			81			48			36			200
Loans charged-off		(146		)		—			—			—			—			(1		)	(147		)
Recoveries		84				4			1			—			11			2			102
Ending balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
Period-ended amount allocated for:
Individually evaluated for impairment		$	99			$	—		$	—		$	—		$	—		$	60		$	159
Collectively evaluated for impairment		1,314				107			1,747			252			279			40			3,739
Ending Balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
Loans:
Individually evaluated for impairment		$	2,742			$	3,011		$	2,062		$	—		$	—		$	177		$	7,992
Collectively evaluated for impairment		129,239				51,232			119,517			12,280			23,965			16,749			$	352,982
Ending Balance		$	131,981			$	54,243		$	121,579		$	12,280		$	23,965		$	16,926		$	360,974
The following tables provide additional detail of the activity in the allowance for loan losses, by portfolio segment, for the six months ended March 31, 2015 and 2014:
Six Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
31-Mar-15									Real Estate			Land Development			Business			and Other
Allowance for loan losses:
Beginning balance		$	1,072			$	757		$	1,412		$	301		$	454		$	76		$	4,072
Provision for loan losses		189				268			139			60			(36		)	30			650
Loans charged-off		(208		)		—			(62		)	—			(14		)	(2		)	(286		)
Recoveries		11				—			18			—			11			7			47
Ending balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
Period-ended amount allocated for:
Individually evaluated for impairment		$	40			$	—		$	—		$	—		$	—		$	57		$	97
Collectively evaluated for impairment		1,024				1,025			1,507			361			415			54			4,386
Ending Balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
Loans:
Individually evaluated for impairment		$	1,683			$	1,874		$	1,085		$	—		$	—		$	278		$	4,920
Collectively evaluated for impairment		148,419				90,320			154,036			20,941			34,569			19,046			467,331
Ending Balance		$	150,102			$	92,194		$	155,121		$	20,941		$	34,569		$	19,324		$	472,251
Six Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
31-Mar-14									Real Estate			Land Development			Business			and Other
Allowance for loan losses:
Beginning balance		$	1,873			$	165		$	1,501		$	374		$	211		$	142		$	4,266
Provision for loan losses		(117		)		(62		)	466			(122		)	202			(17		)	350
Loans charged-off		(442		)		—			(232		)	—			(159		)	(28		)	(861		)
Recoveries		99				4			12			—			25			3			143
Ending balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
Period-ended amount allocated for:
Individually evaluated for impairment		$	99			$	—		$	—		$	—		$	—		$	60		$	159
Collectively evaluated for impairment		1,314				107			1,747			252			279			40			3,739
Ending Balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
Loans:
Individually evaluated for impairment		$	2,742			$	3,011		$	2,062		$	—		$	—		$	177		$	7,992
Collectively evaluated for impairment		129,239				51,232			119,517			12,280			23,965			16,749			$	352,982
Ending Balance		$	131,981			$	54,243		$	121,579		$	12,280		$	23,965		$	16,926		$	360,974
The following tables present additional detail of impaired loans, segregated by segment, as of and for the three and six month periods ended March 31, 2015 and 2014.  The unpaid principal balance represents the recorded balance prior to any partial charge-offs.  The recorded investment represents customer balances net of any partial charge-offs recognized on the loans.  The interest income recognized column represents all interest income reported on either a cash or accrual basis after the loan became impaired.
												Three months ended						Six months ended
31-Mar-15		Unpaid				Recorded			Allowance for			Average			Interest			Average			Interest
		Principal				Investment			Loan Losses			Recorded			Income			Recorded			Income
		Balance							Allocated			Investment			Recognized			Investment			Recognized
With no related allowance recorded:
Single family		$	1,569			$	1,367		$	—		$	1,258		$	12		$	1,310		$	21
Multifamily		1,970				1,874			—			1,884			20			1,894			40
Commercial real estate		1,179				1,085			—			822			15			703			25
Construction and land development		—				—			—			—			—			—			—
Commercial business		—				—			—			—			—			—			—
Consumer and other		301				221			—			262			1			223			2
With an allowance recorded:
Single family		316				316			40			355			4			343			7
Multifamily		—				—			—			—			—			—			—
Commercial real estate		—				—			—			—			—			55			—
Construction and land development		—				—			—			—			—			—			—
Commercial business		—				—			—			—			—			—			—
Consumer and other		57				57			57			58			1			58			1
		$	5,392			$	4,920		$	97		$	4,639		$	53		$	4,586		$	96
												Three months ended						Six months ended
March 31, 2014		Unpaid				Recorded			Allowance for			Average			Interest			Average			Interest
		Principal				Investment			Loan Losses			Recorded			Income			Recorded			Income
		Balance							Allocated			Investment			Recognized			Investment			Recognized
With no related allowance recorded:
Single family		$	2,499			$	2,334		$	—		$	2,467		$	4		$	2,111		$	10
Multifamily		3,366				3,011			—			3,022			36			3,706			73
Commercial real estate		2,134				2,062			—			1,966			13			1,870			28
Construction and land development		—				—			—			—			—			—			—
Commercial business		—				—			—			—			—			—			—
Consumer and other		335				117			—			118			—			127			—
With an allowance recorded:
Single family		1,235				408			99			204			—			510			—
Multifamily		—				—			—			85			—			114			—
Commercial real estate		—				—			—			99			—			126			—
Construction and land development		—				—			—			—			—			64			—
Commercial business		—				—			—			—			—			—			—
Consumer and other		60				60			60			60			1			60			2
		$	9,629			$	7,992		$	159		$	8,021		$	54		$	8,688		$	113
The following is a summary of troubled debt restructured loans (TDRs) at March 31, 2015 and September 30, 2014:
	March 31, 2015				September 30, 2014
Troubled debt restructurings - accrual	$	3,449			$	3,507
Troubled debt restructurings - nonaccrual	—				195
	$	3,449			$	3,702
Modifications of loan terms in a TDR are generally in the form of an extension of payment terms or lowering of the interest rate, although occasionally the Company has reduced the outstanding principal balance.
There were no loans modified in a TDR during the three months ended March 31, 2015 and 2014. There were no loans modified in a TDR during the six months ended March 31, 2015. During the six months ended March 31, 2014, single family loans totaling $88 were modified in a TDR.
There were no re-defaults of TDR that occurred during the three months or six months ended March 31, 2015 and 2014.
Certain of the Bank’s officers, employees, directors, and their associates are loan customers of the Bank.  As of March 31, 2015 and September 30, 2014, loans of approximately $5,333 and $4,653, respectively, were outstanding to such parties.  These loans were made on substantially the same terms as those prevailing for comparable transactions with other persons and do not involve more than the normal risk of collectability.
An analysis of such loans is as follows:
	Six Months Ended March 31, 2015
Balance, beginning	$	4,653
New loans originated	1,159
Draws on lines of credit	131
Principal repayments	(610		)
Balance, ending	$	5,333

Deposits

Deposits	6 Months Ended
	Mar. 31, 2015
Deposits [Abstract]
Deposits	Deposits
	The following table presents the composition of deposits as of:
		March 31, 2015				30-Sep-14
		Amount		Percent		Amount		Percent
	Checking Accounts:
	Noninterest bearing	$	86,814	16.95	%	$	77,790	17.1	%
	Interest bearing	138,605		27.07	%	132,925		29.22	%
		225,419		44.02	%	210,715		46.32	%
	Passbook and Statement Savings	127,028		24.81	%	122,227		26.87	%
	Variable Rate Money Market Accounts	46,752		9.13	%	25,615		5.63	%
	Certificates of Deposit	112,848		22.04	%	96,371		21.18	%
		$	512,047	100	%	$	454,928	100	%
	Certificates of deposit over one hundred thousand dollars totaled $55,170 and $34,853 as of March 31, 2015 and September 30, 2014, respectively.

Regulatory_Capital

Regulatory Capital	6 Months Ended
	Mar. 31, 2015
Regulatory Capital Requirements [Abstract]
Regulatory Capital	Regulatory Capital
	The federal banking agencies have adopted regulations that substantially amend the capital regulations currently applicable to us. These regulations implement the Basel III regulatory capital reforms and changes required by the Dodd-Frank Act.
	Effective January 1, 2015 (with some changes transitioned into full effectiveness over two to four years), the Bank became subject to new capital requirements adopted by the OCC. These new requirements create a new required ratio for common equity Tier 1 ("CETI") capital, increase the leverage and Tier 1 capital ratios, change the risk weight of certain assets for purposes of the risk-based capital ratios, create an additional capital conservation buffer over the required capital ratios and change what qualifies as capital for purposes of meeting these various capital requirements. Beginning in 2016, failure to maintain the required capital conservation buffer will limit the ability of the Bank to pay dividends, repurchase shares or pay discretionary bonuses. The Company is exempt from consolidated capital requirements as those requirements do not apply to certain small bank holding companies with assets under $1 billion.
	Under the new capital regulations, the minimum capital ratios are: (1) CETI capital ratio of 4.5% of risk-weighted assets; (2) a Tier 1 capital ratio of 6.0% of risk-weighted assets: (3) a total capital ratio of 8.0% of risk-weighted assets; and (4) a leverage ratio of 4.0%. CETI generally consists of common stock and retained earnings, subject to applicable regulatory adjustments and deductions.
	There are a number of changes in what constitutes regulatory capital, some of which are subject to transition periods. These changes include the phasing-out of certain instruments as qualifying capital. The Bank does not use any of these instruments. Under the new requirements for total capital, Tier 2 capital is no longer limited to the amount of Tier 1 capital included in total capital. Mortgage servicing rights, certain deferred tax assets and investments in unconsolidated subsidiaries over designated percentages of CETI will be deducted from capital. The Bank has elected to permanently opt-out of the inclusion of accumulated other comprehensive income in our capital calculations, as permitted by the regulations. This opt-out will reduce the impact of market volatility on our regulatory capital levels.
	The new requirements also include changes in the risk-weights of assets to better reflect credit risk and other risk exposures. These include a 150% risk weight (increased from 100%) for certain high volatility commercial real estate acquisition, development and construction loans and for non-residential mortgage loans that are 90 days past due or otherwise in non-accrual status; a 20% (increased from 0%) credit conversion factor for the unused portion of a commitment with an original maturity of one year or less that is not unconditionally cancellable; a 250% risk weight (increased from 100%) for mortgage servicing and deferred tax assets that are not deducted from capital; and increased risk weights (0% to 600%) for equity exposures.
	In addition to the minimum CETI, Tier 1 and total capital ratios, the Bank will have to maintain a capital conservation buffer consisting of additional CETI capital greater than 2.5% of risk-weighted assets above the required minimum levels in order to avoid limitations on paying dividends, engaging in share repurchases, and paying discretionary bonuses based on percentages of eligible retained income that could be utilized for such actions. This new capital conservation buffer requirement will be phased in beginning in January 2016 at 0.625% of risk-weighted assets and increasing each year until fully implemented in January 2019.
	The OCC's prompt corrective action standards changed effective January 1, 2015. Under the new standards, in order to be considered well-capitalized, the Bank must have a CETI ratio of 6.5% (new), a Tier 1 ratio of 8.0% (increased from 6.0%), a total risk-based capital ratio of 10.0% (unchanged) and a leverage ratio of 5.0% (unchanged). The Bank meets all these new requirements, including the full capital conservation buffer.
	The Bank’s actual capital amounts and ratios and those required by the regulatory standards in effect as of the dates presented are as follows:
	At March 31, 2015	Actual						For Capital Adequacy				To Be Well Capitalized Under Prompt Corrective Action Provisions
								Purposes
		Amount			Ratio			Amount		Ratio		Amount		Ratio
	CETI capital (to risk-weighted assets) - Westbury Bank	64,023			13.18	%		21,859		4.5	%	31,574		6.5	%
	Tier 1 capital (to risk-weighted assets) - Westbury Bank	64,023			13.18	%		29,146		6	%	38,861		8	%
	Total capital (to risk-weighted assets) - Westbury Bank	$	68,506		14.11	%		$	38,841	8	%	$	48,551	10	%
	Leverage (to adjusted total assets) - Westbury Bank	64,023			10.57	%		24,228		4	%	30,285		5	%
	At September 30, 2014	Actual						For Capital Adequacy				To Be Well Capitalized Under Prompt Corrective Action Provisions
								Purposes
		Amount			Ratio			Amount		Ratio		Amount		Ratio
	Total capital (to risk-weighted assets) - Westbury Bank	$	65,181		16.18	%		$	32,228	8	%	$	40,285	10	%
	Tier 1 capital (to risk-weighted assets) - Westbury Bank	61,109			15.17	%		16,113		4	%	24,170		6	%
	Tier 1 capital (to adjusted total assets) - Westbury Bank	61,109			11.13	%		21,962		4	%	27,452		5	%
	The following table reconciles the Bank’s stockholders’ equity to regulatory capital as of March 31, 2015 and September 30, 2014:
		March 31,			September 30,
		2015			2014
	Stockholders’ equity of the Bank	$	69,299		$	67,529
	Less: Disallowed servicing assets	—			(162		)
	Unrealized (gain) loss on securities	(438		)	33
	Disallowed investment in subsidiary	(3,296		)	(3,296		)
	Disallowed deferred tax assets	(1,542		)	(2,995		)
	Tier 1 capital and tangible capital	64,023			61,109
	Plus: Allowable general valuation allowances	4,483			4,072
	Risk-based capital	$	68,506		$	65,181

Commitments

Commitments	6 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments	Commitments
	The Company is a party to financial instruments with off-balance-sheet risk in the normal course of business to meet the financing needs of its customers.  These financial instruments include commitments to extend credit and involve, to varying degrees, elements of credit and interest rate risk in excess of the amount recognized in the consolidated balance sheets.  The contractual amounts of those instruments reflect the extent of involvement the Company has in particular classes of financial instruments.
	The Company’s exposure to credit loss in the event of nonperformance by the other party to the financial instruments for commitments to extend credit is represented by the contractual amount of those instruments.  The Company uses the same credit policies in making commitments and conditional obligations as it does for on-balance-sheet instruments.
	The following instruments were outstanding whose contract amounts represent credit risk:
		31-Mar-15		September 30,
				2014
	Commitments to extend mortgage credit:
	Fixed rate	$	2,422	$	960
	Adjustable rate	1,941		3,339
	Unused commercial loan and home equity lines of credit	85,711		61,325
	Standby letters of credit	951		422
	Commitment to sell loans	1,594		326
	Commitments to extend credit are agreements to lend funds to a customer as long as there is no violation of any condition established in the contract.  Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee.  As some such commitments expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements.  The Company evaluates each customer’s creditworthiness on a case-by-case basis.  The Company generally extends credit only on a secured basis.  Collateral obtained varies but consists primarily of single family residences.
	Unfunded commitments under lines of credit are commitments for possible future extensions of credit to existing customers.  These lines of credit may be uncollateralized and ultimately may not be drawn upon to the total extent to which the Company is committed.
	Standby letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party.  Those letters of credit are primarily issued to support public and private borrowing arrangements, and, generally, have terms of one year or less.  The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers.  The Company holds collateral supporting those commitments if deemed necessary.  In the event the customer does not perform in accordance with the terms of the agreement with the third party, the Company would be required to fund the commitment.  The maximum potential amount of future payments the Company could be required to make is represented by the contractual amount shown in the summary above.  If the commitment is funded, the Company would be entitled to seek recovery from the customer.  At March 31, 2015 and September 30, 2014, no amounts have been recorded as liabilities for the Company’s potential obligations under these guarantees.
	Commitments to sell loans are commitments to sell single family mortgage loans to investors on the secondary market.

Fair_Value_Measurements

Fair Value Measurements	6 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	ASC Topic 820, Fair Value Measurements and Disclosures, defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants.  ASC Topic 820 requires the use of valuation techniques that are consistent with the market approach, the income approach and/or the cost approach.  Inputs to valuation techniques refer to the assumptions that market participants would use in pricing the asset or liability.  Inputs may be observable, meaning those that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources, or unobservable, meaning those that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances.  In that regard, ASC Topic 820 establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows:
	Level 1:  Quoted prices (unadjusted) for identical assets or liabilities in active markets that the entity has the ability to access as of the measurement date.
	Level 2:  Significant other observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.
	Level 3:  Significant unobservable inputs that reflect a reporting entity’s own assumptions about the assumptions that market participants would use in pricing an asset or liability.
	A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below.
	Securities available-for-sale:  The fair value of the Company’s securities available-for-sale is determined using Level 2 inputs, which are derived from readily available pricing sources and third-party pricing services for comparable instruments.  The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, treasury yield curves, trading levels, credit information and credit terms, among other factors. In certain cases where Level 1 or Level 2 are not available, securities are classified within Level 3 of the hierarchy.
	Derivatives:  The fair values of the Company’s embedded derivatives related to certain certificates of deposit are determined using inputs that are observable or that can be corroborated by observable market data (such as the S&P 500 Index and the 10- year U.S. Treasury rate) and, therefore, are classified within Level 2 of the valuation hierarchy.
	Assets and liabilities recorded at fair value on a recurring basis:  The following table summarizes assets measured at fair value on a recurring basis, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value as of:
						Fair Value Measurements
	31-Mar-15		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Securities available-for-sale
	U.S. Government and agency securities		$	25		$	—		$	25		$	—
	U.S. Government agency residential mortgage-backed securities		39,184			—			39,184			—
	U.S. Government agency collateralized mortgage obligations		2,400			—			2,400			—
	U.S. Government agency commercial mortgage-backed securities		9,694			—			9,694			—
	Municipal securities		26,578			—			26,578			—
	Total securities available-for-sale		$	77,881		$	—		$	77,881		$	—
	Derivatives		$	151		$	—		$	151		$	—
	Liabilities
	Derivatives		$	151		$	—		$	151		$	—
						Fair Value Measurements
	September 30, 2014		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets  for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Securities available-for-sale
	U.S. Government and agency securities		$	5,179		$	—		$	5,179		$	—
	U.S. Government agency residential mortgage-backed securities		37,196			—			37,196			—
	U.S. Government agency collateralized mortgage obligations		3,432			—			3,432			—
	U.S. Government agency commercial mortgage-backed securities		10,752			—			10,752			—
	Municipal securities		33,787			—			33,787			—
	Total securities available-for-sale		$	90,346		$	—		$	90,346		$	—
	Derivatives		$	87		$	—		$	87		$	—
	Liabilities
	Derivatives		$	87		$	—		$	87		$	—
	The Company did not have any transfers between Level 1, Level 2, and Level 3 of the fair value hierarchy during the six months ended March 31, 2015.  The Company’s policy for determining transfers between levels occurs at the end of the reporting period when circumstances in the underlying valuation criteria change and result in a transfer between levels.
	Assets recorded at fair value on a nonrecurring basis:  The Company may be required, from time to time, to measure certain instruments at fair value on a nonrecurring basis in accordance with U.S. generally accepted accounting principles.
	Impaired loans:  The Company does not record loans at fair value on a recurring basis.  The specific reserves for collateral-dependent impaired loans are based on the fair value of the collateral less estimated costs to sell. The fair value of collateral is determined based on appraisals.  In some cases, adjustments were made to the appraised values due to various factors including age of the appraisal, age of comparables included in the appraisal, and known changes in the market and in the collateral.  When significant adjustments were based on unobservable inputs, the resulting fair value measurement has been categorized as a Level 3 measurement.  Impaired loans with a carrying amount of $373 and $541 have a valuation allowance of $97 and $136 included in the allowance for loan losses to reflect their fair value as of March 31, 2015 and September 30, 2014, respectively.
	Foreclosed real estate:  The Company does not record foreclosed real estate owned at a fair value on a recurring basis.  The fair value of foreclosed real estate was determined using Level 3 inputs based on appraisals or broker pricing opinions.  In some cases, adjustments were made to these values due to various factors including the age of the appraisal, age of comparables included in the appraisal, and known changes in the market and in collateral.  Foreclosed real estate is measured at fair value less estimated costs to sell at the date of foreclosure.  Subsequent to foreclosure, additional writedowns may be recorded based on changes to the fair value of the assets.
	Mortgage servicing rights:  Mortgage servicing rights ("MSRs") do not trade in an active, open market with readily observable prices.  While sales of MSRs do occur, the precise terms and conditions typically are not readily available.  Accordingly, the Company estimates the fair value of MSRs using discounted cash flow models incorporating numerous assumptions from the perspective of market participants including servicing income, servicing costs, market discount rates, prepayments speeds, and default rates.  Due to the nature of the valuation inputs, MSRs are classified within Level 3 of the valuation hierarchy.  As of March 31, 2015, mortgage servicing rights with a carrying amount of $1,569 have a valuation allowance of $160 to reflect their fair value of $1,409.  As of September 30, 2014, mortgage servicing rights with a carrying amount of $1,784 have a valuation allowance of $160 to reflect their fair value of $1,624.
						Fair Value Measurements
	31-Mar-15		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Impaired loans		$	276		$	—		$	—		$	276
	Foreclosed real estate		2,100			—			—			2,100
	Mortgage servicing rights		1,409			—			—			1,409
						Fair Value Measurements
	September 30, 2014		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Impaired loans		$	405		$	—		$	—		$	405
	Foreclosed real estate		2,355			—			—			2,355
	Mortgage servicing rights		1,624			—			—			1,624
Disclosure of fair value information about financial instruments, for which it is practicable to estimate that value, is required whether or not recognized in the consolidated balance sheets.  In cases where quoted market prices are not available, fair values are based on estimates using present value or other valuation techniques.  Those techniques are significantly affected by the assumptions used, including the discount rate and estimates of future cash flows.  In that regard, the derived fair value estimates cannot be substantiated by comparison to independent markets and, in many cases, could not be realized in immediate settlement of the instruments.  Certain financial instruments with a fair value that is not practicable to estimate and all non-financial instruments are excluded from the disclosure requirements.  Accordingly, the aggregate fair value amounts presented do not necessarily represent the underlying value of the Company for assets and liabilities not previously described.  The Company, in estimating its fair value disclosures for financial instruments not described above, used the following methods and assumptions:
Cash and cash equivalents:  The carrying amounts of cash and cash equivalents reported in the consolidated balance sheets approximate those assets’ fair values.
Securities held to maturity: The fair values of securities held to maturity are based on quoted market prices for similar securities, adjusted for differences in security characteristics.
Loans:  For variable-rate mortgage loans that re-price frequently and with no significant change in credit risk, fair values are based on carrying values.  The fair values for fixed rate residential mortgage loans are based on quoted market prices for similar loans sold in conjunction with sale transactions, adjusted for differences in loan characteristics.  The fair values for commercial real estate loans, rental property mortgage loans, and consumer and other loans are estimated using discounted cash flow analyses and using interest rates currently being offered for loans with similar terms to borrowers of similar credit quality.
Loans held for sale:  Fair value of loans held for sale are based on commitments on hand from investors or prevailing market prices.
Federal Home Loan Bank stock:  The carrying amount of FHLB stock approximates its fair value based on the redemption provisions of the FHLB.
Accrued interest receivable and payable:  The carrying amounts of accrued interest receivable and payable approximate their fair values.
Deposits:  The fair value disclosed for interest-bearing and non-interest-bearing checking accounts, savings accounts, and money market accounts are equal to the amount payable on demand at the reporting date (i.e., their carrying amounts).  The fair values of fixed rate certificates of deposit are estimated using a discounted cash flow calculation that applies interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities of the outstanding certificates of deposit.
Advances from the Federal Home Loan Bank:  The fair values of FHLB advances are estimated using discounted cash flow analyses, based on the Company’s current incremental borrowing rates for similar types of borrowing arrangements.
Advance payments by borrowers for property taxes and insurance:  The carrying amounts of the advance payments by borrowers for property taxes and insurance approximate their fair values.
Mortgage banking derivatives:  The fair value of commitments to originate mortgage loans held for sale is estimated by comparing the Company’s cost to acquire mortgages and the current price for similar mortgage loans, taking into account the terms of the commitments and the credit worthiness of the counterparties.  The fair value of forward commitments to sell residential mortgage loans is the estimated amount that the Bank would receive or pay to terminate the forward delivery contract at the reporting date based on market prices for similar financial instruments.  The fair value of these derivative financial instruments was not material at March 31, 2015 and September 30, 2014.
The estimated fair values and related carrying amounts of the Company’s financial instruments are as follows:
	31-Mar-15
	Carrying			Estimated Fair			Quoted Prices in			Significant Other			Significant Other
	Amount			Value			Active Markets for			Observable			Unobservable
							Identical Assets			Inputs			Inputs
							(Level 1)			(Level 2)			(Level 3)
Financial assets:
Cash and cash equivalents	$	16,805		$	16,805		$	16,805		$	—		$	—
Securities available for sale	77,881			77,881			—			77,881			—
Securities held to maturity	3,025			3,042			—			3,042			—
Loans, net	467,447			467,980			—			—			467,980
Loans held for sale, net	1,594			1,594			—			1,594			—
Federal Home Loan Bank stock	3,350			3,350			—			—			3,350
Mortgage servicing rights	1,409			1,409			—			—			1,409
Accrued interest receivable	1,930			1,930			1,930			—			—
Derivative asset	151			151			—			151			—
Financial liabilities:
Deposits	512,047			489,066			86,814			—			402,252
Advances from Federal Home Loan Bank	13,000			13,000			—			13,000			—
Advance payments by borrowers for property taxes and insurance	1,966			1,966			1,966			—			—
Accrued interest payable	4			4			4			—			—
Derivative liability	151			151			—			151			—
	30-Sep-14
	Carrying			Estimated Fair			Quoted Prices in			Significant Other			Significant Other
	Amount			Value			Active Markets for			Observable			Unobservable
							Identical Assets			Inputs			Inputs
							(Level 1)			(Level 2)			(Level 3)
Financial assets:
Cash and cash equivalents	$	17,608		$	17,608		$	17,608		$	—		$	—
Securities available for sale	90,346			90,346			—			90,346			—
Loans, net	416,874			415,857			—			—			415,857
Loans held for sale, net	326			326			—			326			—
Federal Home Loan Bank stock	2,670			2,670			—			—			2,670
Mortgage servicing rights	1,624			1,624			—			—			1,624
Accrued interest receivable	1,784			1,784			1,784			—			—
Derivative asset	87			87			—			87			—
Financial liabilities:
Deposits	454,928			442,342			77,790			—			364,552
Advances from Federal Home Loan Bank	17,000			17,000			—			17,000			—
Advance payments by borrowers for property taxes and insurance	5,869			5,869			5,869			—			—
Accrued interest payable	3			3			3			—			—
Derivative liability	87			87			—			87			—

Employee_Stock_Ownership_Plan

Employee Stock Ownership Plan	6 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee Stock Ownership Plan	Employee Stock Ownership Plan
	The Bank maintains a leveraged employee stock ownership plan ("ESOP") that covers all employees meeting certain minimum age and service requirements. The ESOP was established in conjunction with the Company's stock offering completed in April 2013 and operates on a plan year ending December 31. The ESOP initially borrowed $4.1 million from the Company and used those funds to acquire 411,403 shares, or 8.0% of the total number of shares issued by the Company in its initial public offering. The shares were acquired at a price of $10.00 per share. The Bank makes annual contributions to the ESOP equal to the ESOP's debt service. The ESOP shares were pledged as collateral for its debt. As the debt is repaid, shares are released from collateral and allocated to active participants, based on the proportion of debt service paid in the year. The debt repayment and release of shares generally occurs at December 31, the plan year end date. The Company accounts for its ESOP in accordance with ASC 718-40. Accordingly, because the debt is intercompany, it is eliminated in consolidation for presentation in these statements. The shares pledged as collateral are reported as unearned ESOP shares in the balance sheet. Total ESOP shares may be reduced as a result of employees leaving the Company as shares that have previously been released to those exiting employees may be removed from the ESOP and transferred to that employee. As shares are committed to be released from collateral, the Company reports compensation expense equal to the current market price of the shares, and the shares become outstanding for EPS computations. During the three months ended March 31, 2015, 5,142 shares were committed to be released. The total ESOP compensation expense recorded for the three months ended March 31, 2015 and 2014 was $86 and $72 respectively. During the six months ended March 31, 2015, 10,284 shares were committed to be released, 5,142 of which were released and available for allocation at December 31, 2014 concurrent with the payment of the annual debt service on the ESOP loan. The total ESOP compensation expense recorded for the six months ended March 31, 2015 and 2014 was $198 and $168 respectively.
	The ESOP shares as of March 31, 2015 and September 30, 2014 were as follows (in thousands, except share data):
		31-Mar-15				September 30, 2014
	Allocated shares to active participants	36,442				20,570
	Shares committed to be released	5,142				15,428
	Unallocated shares	365,121				375,405
	Total ESOP shares	406,705				411,403
	Fair value of unallocated shares	$	6,390			$	5,650
	Compensation Plans
	ASC Topic 718 requires that the grant date fair value of equity awards to employees be recognized as compensation expense over the period during which an employee is required to provide service in exchange for such award.
	The following table summarizes the impact of the Company's share-based payment plans in the financial statements for the periods shown:
		Three Months Ended March 31,							Six Months Ended March 31,
		2015				2014			2015		2014
	Total cost of stock grant plan during the year	$	155			$	—		$	310	$	—
	Total cost of stock option plan during the year	46				—			92		—
	Total cost of share-based payment plans during the year	$	201			$	—		$	402	—
	Amount of related income tax benefit recognized in income	$	79			$	—		$	158	$	—
	The Company adopted the Westbury Bancorp Inc 2014 Equity Incentive Plan (the "Plan") in 2014. In June 2014, the Company's stockholders approved the Plan which authorized the issue of up to 203,665 restricted stock awards and up to 509,162 stock options. As of March 31, 2015 there were no restricted stock awards and 182,938 options available for future grants.
	Annual equity-based incentive awards are typically granted to selected officers and employees mid-year. Options are granted with an exercise price equal to no less than the market price of the Company's shares at the date of grant: those option awards generally vest over five years of service and have 10-year contractual terms. Restricted shares and units typically vest over a five year period. Equity awards may also be granted at other times throughout the year in connection with the recruitment and retention of officers and employees.
	The following table summarizes stock options outstanding for the three and six months ended March 31, 2015:
		Number of Options		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
	Options outstanding as of December 31, 2014	326,224		$	15.2
	Granted	—		—
	Exercised	—		—
	Expired or canceled	—		—
	Forfeited	—		—
	Options outstanding as of March 31, 2015	326,224		$	15.2		9.25	$	750
	Options exercisable as of March 31, 2015	—		$	—		—	$	—
		Number of Options		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
	Options outstanding as of September 30, 2014	326,224		$	15.2
	Granted	—		—
	Exercised	—		—
	Expired or canceled	—		—
	Forfeited	—		—
	Options outstanding as of March 31, 2015	326,224		$	15.2		9.25	$	750
	Options exercisable as of March 31, 2015	—		$	—		—	$	—
	The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model based on certain assumptions. Expected volatility is based on historical volatility and the expectations of future volatility of Company shares. The risk free interest rate for periods within the contractual term of the option is based on the U.S. Treasury yield curve in effect at the time of the grant. The expected life of options is estimated based on historical employee behavior and represents the period of time that options granted are expected to remain outstanding.
	The following assumptions were used for options granted during the year ended September 30, 2014:
	Risk-free interest rate	2.1		%
	Expected volatility of Company's stock	9.49		%
	Expected dividend yield	—		%
	Expected life of options (years)	7.5
	Weighted average fair value per option of options granted during the year	$	2.82
	The total intrinsic value of options exercised during the three and six months ended March 31, 2015 was $0.
	The following is a summary of changes in restricted shares for the three and six months ended March 31, 2015:
		Number of Shares			Weighted Average Grant Date Fair Value
	Shares Outstanding at December 31, 2014	203,665			$	15.2
	Granted	—			—
	Vested	—			—
	Forfeited	—			—
	Shares Outstanding at March 31, 2015	203,665			$	15.2
		Number of Shares			Weighted Average Grant Date Fair Value
	Shares Outstanding at September 30, 2014	203,665			$	15.2
	Granted	—			—
	Vested	—			—
	Forfeited	—			—
	Shares Outstanding at March 31, 2015	203,665			$	15.2
	The total intrinsic value of restricted shares that vested during the six months ended March 31, 2015 was $0.
	As of March 31, 2015, there was $3.4 million of total unrecognized compensation cost related to nonvested share-based compensation arrangements (including share option and nonvested share awards) granted under the Plan. At March 31, 2015, the weighted-average period over which the unrecognized compensation expense is expected to be recognized was approximately 4.25 years.

Compensation_Equity_Plans_Note

Compensation Equity Plans (Notes)	6 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation Equity Plans	Employee Stock Ownership Plan
	The Bank maintains a leveraged employee stock ownership plan ("ESOP") that covers all employees meeting certain minimum age and service requirements. The ESOP was established in conjunction with the Company's stock offering completed in April 2013 and operates on a plan year ending December 31. The ESOP initially borrowed $4.1 million from the Company and used those funds to acquire 411,403 shares, or 8.0% of the total number of shares issued by the Company in its initial public offering. The shares were acquired at a price of $10.00 per share. The Bank makes annual contributions to the ESOP equal to the ESOP's debt service. The ESOP shares were pledged as collateral for its debt. As the debt is repaid, shares are released from collateral and allocated to active participants, based on the proportion of debt service paid in the year. The debt repayment and release of shares generally occurs at December 31, the plan year end date. The Company accounts for its ESOP in accordance with ASC 718-40. Accordingly, because the debt is intercompany, it is eliminated in consolidation for presentation in these statements. The shares pledged as collateral are reported as unearned ESOP shares in the balance sheet. Total ESOP shares may be reduced as a result of employees leaving the Company as shares that have previously been released to those exiting employees may be removed from the ESOP and transferred to that employee. As shares are committed to be released from collateral, the Company reports compensation expense equal to the current market price of the shares, and the shares become outstanding for EPS computations. During the three months ended March 31, 2015, 5,142 shares were committed to be released. The total ESOP compensation expense recorded for the three months ended March 31, 2015 and 2014 was $86 and $72 respectively. During the six months ended March 31, 2015, 10,284 shares were committed to be released, 5,142 of which were released and available for allocation at December 31, 2014 concurrent with the payment of the annual debt service on the ESOP loan. The total ESOP compensation expense recorded for the six months ended March 31, 2015 and 2014 was $198 and $168 respectively.
	The ESOP shares as of March 31, 2015 and September 30, 2014 were as follows (in thousands, except share data):
		31-Mar-15				September 30, 2014
	Allocated shares to active participants	36,442				20,570
	Shares committed to be released	5,142				15,428
	Unallocated shares	365,121				375,405
	Total ESOP shares	406,705				411,403
	Fair value of unallocated shares	$	6,390			$	5,650
	Compensation Plans
	ASC Topic 718 requires that the grant date fair value of equity awards to employees be recognized as compensation expense over the period during which an employee is required to provide service in exchange for such award.
	The following table summarizes the impact of the Company's share-based payment plans in the financial statements for the periods shown:
		Three Months Ended March 31,							Six Months Ended March 31,
		2015				2014			2015		2014
	Total cost of stock grant plan during the year	$	155			$	—		$	310	$	—
	Total cost of stock option plan during the year	46				—			92		—
	Total cost of share-based payment plans during the year	$	201			$	—		$	402	—
	Amount of related income tax benefit recognized in income	$	79			$	—		$	158	$	—
	The Company adopted the Westbury Bancorp Inc 2014 Equity Incentive Plan (the "Plan") in 2014. In June 2014, the Company's stockholders approved the Plan which authorized the issue of up to 203,665 restricted stock awards and up to 509,162 stock options. As of March 31, 2015 there were no restricted stock awards and 182,938 options available for future grants.
	Annual equity-based incentive awards are typically granted to selected officers and employees mid-year. Options are granted with an exercise price equal to no less than the market price of the Company's shares at the date of grant: those option awards generally vest over five years of service and have 10-year contractual terms. Restricted shares and units typically vest over a five year period. Equity awards may also be granted at other times throughout the year in connection with the recruitment and retention of officers and employees.
	The following table summarizes stock options outstanding for the three and six months ended March 31, 2015:
		Number of Options		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
	Options outstanding as of December 31, 2014	326,224		$	15.2
	Granted	—		—
	Exercised	—		—
	Expired or canceled	—		—
	Forfeited	—		—
	Options outstanding as of March 31, 2015	326,224		$	15.2		9.25	$	750
	Options exercisable as of March 31, 2015	—		$	—		—	$	—
		Number of Options		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
	Options outstanding as of September 30, 2014	326,224		$	15.2
	Granted	—		—
	Exercised	—		—
	Expired or canceled	—		—
	Forfeited	—		—
	Options outstanding as of March 31, 2015	326,224		$	15.2		9.25	$	750
	Options exercisable as of March 31, 2015	—		$	—		—	$	—
	The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model based on certain assumptions. Expected volatility is based on historical volatility and the expectations of future volatility of Company shares. The risk free interest rate for periods within the contractual term of the option is based on the U.S. Treasury yield curve in effect at the time of the grant. The expected life of options is estimated based on historical employee behavior and represents the period of time that options granted are expected to remain outstanding.
	The following assumptions were used for options granted during the year ended September 30, 2014:
	Risk-free interest rate	2.1		%
	Expected volatility of Company's stock	9.49		%
	Expected dividend yield	—		%
	Expected life of options (years)	7.5
	Weighted average fair value per option of options granted during the year	$	2.82
	The total intrinsic value of options exercised during the three and six months ended March 31, 2015 was $0.
	The following is a summary of changes in restricted shares for the three and six months ended March 31, 2015:
		Number of Shares			Weighted Average Grant Date Fair Value
	Shares Outstanding at December 31, 2014	203,665			$	15.2
	Granted	—			—
	Vested	—			—
	Forfeited	—			—
	Shares Outstanding at March 31, 2015	203,665			$	15.2
		Number of Shares			Weighted Average Grant Date Fair Value
	Shares Outstanding at September 30, 2014	203,665			$	15.2
	Granted	—			—
	Vested	—			—
	Forfeited	—			—
	Shares Outstanding at March 31, 2015	203,665			$	15.2
	The total intrinsic value of restricted shares that vested during the six months ended March 31, 2015 was $0.
	As of March 31, 2015, there was $3.4 million of total unrecognized compensation cost related to nonvested share-based compensation arrangements (including share option and nonvested share awards) granted under the Plan. At March 31, 2015, the weighted-average period over which the unrecognized compensation expense is expected to be recognized was approximately 4.25 years.

Condensed_Parent_Company_Finan

Condensed Parent Company Financial Information (Notes)	6 Months Ended
	Mar. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Financial Information	Condensed Parent Company Financial Information
	The condensed financial statements of Westbury Bancorp, Inc. (parent company only) are presented below:
	Balance Sheets
	(In thousands)
		March 31,			September 30,
		2015			2014
	Assets
	Cash and interest bearing deposits	$	2,775		$	6,878
	Investments	1,424			6,590
	Loan to ESOP	3,778			3,931
	Investment in subsidiary	72,702			71,131
	Other assets	1,992			1,674
	Total assets	$	82,671		$	90,204
	Liabilities and Stockholders' Equity
	Total liabilities	$	131		$	115
	Stockholders' equity	82,540			90,089
	Total liabilities and stockholders' equity	$	82,671		$	90,204
	Statements of Operations
	(In thousands)
		Three Months Ended March 31,						Six Months Ended March 31,
		2015			2014			2015			2014
	Interest and other income	$	63		$	71		$	126		$	141
	Interest and other expense	165			261			349			448
	Loss before income tax benefit and equity in undistributed net income of subsidiary	(102		)	(190		)	(223		)	(307		)
	Income tax benefit	(24		)	(61		)	(54		)	(93		)
	Loss before equity in undistributed net income (loss) of subsidiary	(78		)	(129		)	(169		)	(214		)
	Equity in undistributed net income (loss) of subsidiary	562			(1,670		)	1,100			(1,517		)
	Net income (loss)	$	484		$	(1,799	)	$	931		$	(1,731	)
	Statements of Cash Flows
	(in thousands)
		For Six Months Ended March 31,
		2015			2014
	Cash Flows From Operating Activities
	Net income (loss)	$	931		$	(1,731	)
	Adjustments to reconcile net income (loss) to net cash used in operating activities:
	Equity in undistributed net income (loss) of subsidiary	(1,100		)	1,517
	Net change in other liabilities	16			6
	Net change in other assets	100			47
	Net cash used in operating activities	(53		)	(161		)
	Cash Flows From Investing Activities
	Purchase of securities	(728		)	(663		)
	Sales and maturities of securities	5,894			706
	Payments received on ESOP loan	153			183
	Net cash provided by investing activities	5,319			226
	Cash Flows From Financing Activities
	Repurchase of common stock	(9,369		)	—
	Net cash used in financing activities	(9,369		)	—
	Net increase (decrease) in cash	(4,103		)	65
	Cash
	Beginning of period	6,878			9,271
	End of period	$	2,775		$	9,336

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	6 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Schedule of calculated earnings per share, basic and diluted	The following table presents a reconciliation of the number of shares used in the calculation of basic and diluted earnings per common share (in thousands, except share and per share data).
		Three Months Ended						Six Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
	Net income (loss)	$	484		$	(1,799	)	$	931		$	(1,731	)
	Basic potential common shares:
	Weighted average shares outstanding	4,657,638			5,142,541			4,746,438			5,142,541
	Weighted average unallocated ESOP shares	(368,549		)	(387,405		)	(371,149		)	(390,262		)
	Basic weighted average shares outstanding	4,289,089			4,755.14			4,375,289			4,752.28
	Dilutive effect of equity awards	33,670			—			28,971			—
	Diluted weighted average shares outstanding	4,322,759			4,755,136			4,404,260			4,752,279
	Basic income (loss) per share	$	0.11		$	(0.38	)	$	0.21		$	(0.36	)
	Diluted income (loss) per share	$	0.11		$	(0.38	)	$	0.21		$	(0.36	)

Investment_Securitites_Tables

Investment Securitites (Tables)	6 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Schedule of amortized costs and fair values of securities available-for-sale	The amortized cost and fair value of investment securities are summarized as follows:
		31-Mar-15
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			(Losses)
	Available for Sale
	U.S. Government and agency securities	$	24	$	1		$	—		$	25
	U.S. Government agency residential mortgage-backed securities	38,762		534			(112		)	39,184
	U.S. Government agency collateralized mortgage obligations	2,424		23			(47		)	2,400
	U.S. Government agency commercial mortgage-backed securities	9,617		77			—			9,694
	Municipal securities	26,328		278			(28		)	26,578
	Total Available for Sale	77,155		913			(187		)	77,881
	Held to Maturity
	Municipal securities	3,025		17			—			3,042
	Total Investment Securities	$	80,180	$	930		$	(187	)	$	80,923
		30-Sep-14
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			(Losses)
	Available for Sale
	U.S. Government and agency securities	$	5,250	$	—		$	(71	)	$	5,179
	U.S. Government agency residential mortgage-backed securities	37,144		389			(337		)	37,196
	U.S. Government agency collateralized mortgage obligations	3,458		30			(56		)	3,432
	U.S. Government agency commercial mortgage-backed securities	10,835		11			(94		)	10,752
	Municipal securities	33,735		280			(228		)	33,787
	Total Available for Sale	90,422		710			(786		)	90,346
	Held to Maturity
	Municipal securities	—		—			—			—
	Total Investment Securities	$	90,422	$	710		$	(786	)	$	90,346
Schedule of amortized cost and estimated fair value of investment securities by contractual maturity	The amortized cost and fair value of investment securities, by contractual maturity at March 31, 2015 are shown in the following table.  Actual maturities differ from contractual maturities for mortgage-backed securities because the mortgages underlying the securities may be called or repaid without penalty.  Therefore, these securities are not presented in the maturity categories in the table below.
		31-Mar-15
		Amortized Cost		Fair Value
	Available for sale:
	Due in one year or less	$	2,447	$	2,475
	Due after one year through five years	14,696		14,865
	Due after five years through ten years	7,604		7,671
	Due after ten years	1,605		1,592
	U.S. Government agency collateralized mortgage obligations	2,424		2,400
	U.S. Government agency residential mortgage-backed securities	38,762		39,184
	U.S. Government agency commercial mortgage-backed securities	9,617		9,694
		77,155		77,881
	Held to maturity:
	Due in one year or less	566		566
	Due after one year through five years	679		680
	Due after five years through ten years	929		937
	Due after ten years	851		859
		3,025		3,042
	Total	$	80,180	$	80,923
Schedule of investment securities in an unrealized loss position	Information pertaining to securities with gross unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, are summarized as follows:
		31-Mar-15
		Less than 12 Months					12 Months or Longer						Total
		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
		Value		Loss			Value			Loss			Value		Loss
	U.S. Government and agency securities	$	—	$	—		$	—		$	—		$	—	$	—
	U.S. Government agency residential mortgage-backed securities	3,858		(13		)	8,321			(99		)	12,179		(112		)
	U.S. Government agency collateralized mortgage obligations	—		—			753			(47		)	753		(47		)
	U.S Government agency commercial mortgage-backed securities	—		—			—			—			—		—
	Municipal securities	2,008		(13		)	1,690			(15		)	3,698		(28		)
		$	5,866	$	(26	)	$	10,764		$	(161	)	$	16,630	$	(187	)
		30-Sep-14
		Less than 12 Months					12 Months or Longer						Total
		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
		Value		Loss			Value			Loss			Value		Loss
	U.S. Government and agency securities	$	—	$	—		$	5,179		$	(71	)	$	5,179	$	(71	)
	U.S. Government agency residential mortgage-backed securities	9,617		(54		)	13,075			(283		)	22,692		(337		)
	U.S. Government agency collateralized mortgage obligations	—		—			891			(56		)	891		(56		)
	U.S. Government agency commercial mortgage-backed securities	6,235		(73		)	1,033			(21		)	7,268		(94		)
	Municipal securities	3,046		(8		)	13,621			(220		)	16,667		(228		)
		$	18,898	$	(135	)	$	33,799		$	(651	)	$	52,697	$	(786	)

Loans_Tables

Loans (Tables)	6 Months Ended
	Mar. 31, 2015
Loans
Summary of balances of loans	A summary of the balances of loans follows:
		March 31, 2015				September 30,
						2014
	Real estate:
	Single family	$	150,102			$	135,337
	Multifamily	92,194				76,396
	Commercial real estate	155,121				135,121
	Construction and land development	20,941				16,362
	Total real estate	418,358				363,216
	Commercial business	34,569				37,675
	Consumer:
	Home equity lines of credit	12,608				14,275
	Education	4,374				4,694
	Other	2,342				1,321
	Total consumer	19,324				20,290
	Total loans	472,251				421,181
	Less:
	Net deferred loan fees	321				235
	Allowance for loan losses	4,483				4,072
	Net loans	$	467,447			$	416,874
Schedule of contractual aging of recorded investment in past due loans	The following tables present the contractual aging of the recorded investment in past due loans by class of loans as of March 31, 2015 and September 30, 2014:
	March 31, 2015		Current				30-59 Days			60-89 Days			Loans Past			Total
							Past Due			Past Due			Due 90 Days
													or More
	Single family		$	148,804			$	1,016		$	—		$	282		$	150,102
	Multifamily		92,194				—			—			—			92,194
	Commercial real estate		154,727				—			—			394			155,121
	Construction and land development		20,941				—			—			—			20,941
	Commercial business		34,567				2			—			—			34,569
	Consumer and other:
	Home equity lines of credit		12,428				—			—			180			12,608
	Education		4,180				54			66			74			4,374
	Other		2,342				—			—			—			2,342
			$	470,183			$	1,072		$	66		$	930		$	472,251
	September 30, 2014		Current				30-59 Days			60-89 Days			Loans Past			Total
							Past Due			Past Due			Due 90 Days
													or More
	Single family		$	133,102			$	1,623		$	162		$	450		$	135,337
	Multifamily		76,396				—			—			—			76,396
	Commercial real estate		134,584				178			163			196			135,121
	Construction and land development		16,362				—			—			—			16,362
	Commercial business		37,653				—			—			22			37,675
	Consumer and other:
	Home equity lines of credit		13,918				228			—			129			14,275
	Education		4,502				28			44			120			4,694
	Other		1,319				—			—			2			1,321
			$	417,836			$	2,057		$	369		$	919		$	421,181
Schedule of risk category of loans	The following tables present the risk category of loans evaluated by internal asset classification based on the most recent analysis performed and the contractual aging as of March 31, 2015 and September 30, 2014:
	March 31, 2015		Pass				Watch			Special Mention			Substandard			Doubtful			Total
	Single family		$	147,649			$	1,151		$	—		$	1,302		$	—		$	150,102
	Multifamily		88,915				2,841			438			—			—			92,194
	Commercial real estate		148,027				4,931			961			1,202			—			155,121
	Construction and land development		20,941				—			—			—			—			20,941
	Commercial business		31,284				3,147			—			138			—			34,569
	Consumer and other:
	Home equity lines of credit		12,343				—			—			265			—			12,608
	Education		4,374				—			—			—			—			4,374
	Other		2,342				—			—			—			—			2,342
	Total		$	455,875			$	12,070		$	1,399		$	2,907		$	—		$	472,251
	September 30, 2014		Pass				Watch			Special Mention			Substandard			Doubtful			Total
	Single family		$	132,067			$	1,317		$	118		$	1,835		$	—		$	135,337
	Multifamily		73,876				1,915			445			160			—			76,396
	Commercial real estate		126,319				6,117			858			1,827			—			135,121
	Construction and land development		16,357				—			—			5			—			16,362
	Commercial business		34,112				3,459			—			104			—			37,675
	Consumer and other:
	Home equity lines of credit		14,088				—			—			187			—			14,275
	Education		4,694				—			—			—			—			4,694
	Other		1,319				—			—			2			—			1,321
			$	402,832			$	12,808		$	1,421		$	4,120		$	—		$	421,181
Schedule of activity in the allowance for loan losses, by portfolio segment	The following tables provide additional detail of the activity in the allowance for loan losses, by portfolio segment, for the three months ended March 31, 2015 and 2014:
	Three Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
	31-Mar-15									Real Estate			Land Development			Business			and Other
	Allowance for loan losses:
	Beginning balance		$	1,025			$	932		$	1,388		$	367		$	412		$	100		$	4,224
	Provision for loan losses		86				93			124			(6		)	(2		)	5			300
	Loans charged-off		(47		)		—			(14		)	—			—			—			(61		)
	Recoveries		—				—			9			—			5			6			20
	Ending balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
	Period-ended amount allocated for:
	Individually evaluated for impairment		$	40			$	—		$	—		$	—		$	—		$	57		$	97
	Collectively evaluated for impairment		1,024				1,025			1,507			361			415			54			4,386
	Ending Balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
	Loans:
	Individually evaluated for impairment		$	1,683			$	1,874		$	1,085		$	—		$	—		$	278		$	4,920
	Collectively evaluated for impairment		148,419				90,320			154,036			20,941			34,569			19,046			467,331
	Ending Balance		$	150,102			$	92,194		$	155,121		$	20,941		$	34,569		$	19,324		$	472,251
	Three Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
	31-Mar-14									Real Estate			Land Development			Business			and Other
	Allowance for loan losses:
	Beginning balance		$	1,658			$	138		$	1,493		$	171		$	220		$	63		$	3,743
	Provision for loan losses		(183		)		(35		)	253			81			48			36			200
	Loans charged-off		(146		)		—			—			—			—			(1		)	(147		)
	Recoveries		84				4			1			—			11			2			102
	Ending balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
	Period-ended amount allocated for:
	Individually evaluated for impairment		$	99			$	—		$	—		$	—		$	—		$	60		$	159
	Collectively evaluated for impairment		1,314				107			1,747			252			279			40			3,739
	Ending Balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
	Loans:
	Individually evaluated for impairment		$	2,742			$	3,011		$	2,062		$	—		$	—		$	177		$	7,992
	Collectively evaluated for impairment		129,239				51,232			119,517			12,280			23,965			16,749			$	352,982
	Ending Balance		$	131,981			$	54,243		$	121,579		$	12,280		$	23,965		$	16,926		$	360,974
	The following tables provide additional detail of the activity in the allowance for loan losses, by portfolio segment, for the six months ended March 31, 2015 and 2014:
	Six Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
	31-Mar-15									Real Estate			Land Development			Business			and Other
	Allowance for loan losses:
	Beginning balance		$	1,072			$	757		$	1,412		$	301		$	454		$	76		$	4,072
	Provision for loan losses		189				268			139			60			(36		)	30			650
	Loans charged-off		(208		)		—			(62		)	—			(14		)	(2		)	(286		)
	Recoveries		11				—			18			—			11			7			47
	Ending balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
	Period-ended amount allocated for:
	Individually evaluated for impairment		$	40			$	—		$	—		$	—		$	—		$	57		$	97
	Collectively evaluated for impairment		1,024				1,025			1,507			361			415			54			4,386
	Ending Balance		$	1,064			$	1,025		$	1,507		$	361		$	415		$	111		$	4,483
	Loans:
	Individually evaluated for impairment		$	1,683			$	1,874		$	1,085		$	—		$	—		$	278		$	4,920
	Collectively evaluated for impairment		148,419				90,320			154,036			20,941			34,569			19,046			467,331
	Ending Balance		$	150,102			$	92,194		$	155,121		$	20,941		$	34,569		$	19,324		$	472,251
	Six Months Ended		Single Family				Multifamily			Commercial			Construction and			Commercial			Consumer			Total
	31-Mar-14									Real Estate			Land Development			Business			and Other
	Allowance for loan losses:
	Beginning balance		$	1,873			$	165		$	1,501		$	374		$	211		$	142		$	4,266
	Provision for loan losses		(117		)		(62		)	466			(122		)	202			(17		)	350
	Loans charged-off		(442		)		—			(232		)	—			(159		)	(28		)	(861		)
	Recoveries		99				4			12			—			25			3			143
	Ending balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
	Period-ended amount allocated for:
	Individually evaluated for impairment		$	99			$	—		$	—		$	—		$	—		$	60		$	159
	Collectively evaluated for impairment		1,314				107			1,747			252			279			40			3,739
	Ending Balance		$	1,413			$	107		$	1,747		$	252		$	279		$	100		$	3,898
	Loans:
	Individually evaluated for impairment		$	2,742			$	3,011		$	2,062		$	—		$	—		$	177		$	7,992
Collectively evaluated for impairment		129,239				51,232			119,517			12,280			23,965			16,749			$	352,982
Ending Balance		$	131,981			$	54,243		$	121,579		$	12,280		$	23,965		$	16,926		$	360,974
Schedule of impaired loans
													Three months ended						Six months ended
	31-Mar-15		Unpaid				Recorded			Allowance for			Average			Interest			Average			Interest
			Principal				Investment			Loan Losses			Recorded			Income			Recorded			Income
			Balance							Allocated			Investment			Recognized			Investment			Recognized
	With no related allowance recorded:
	Single family		$	1,569			$	1,367		$	—		$	1,258		$	12		$	1,310		$	21
	Multifamily		1,970				1,874			—			1,884			20			1,894			40
	Commercial real estate		1,179				1,085			—			822			15			703			25
	Construction and land development		—				—			—			—			—			—			—
	Commercial business		—				—			—			—			—			—			—
	Consumer and other		301				221			—			262			1			223			2
	With an allowance recorded:
	Single family		316				316			40			355			4			343			7
	Multifamily		—				—			—			—			—			—			—
	Commercial real estate		—				—			—			—			—			55			—
	Construction and land development		—				—			—			—			—			—			—
	Commercial business		—				—			—			—			—			—			—
	Consumer and other		57				57			57			58			1			58			1
			$	5,392			$	4,920		$	97		$	4,639		$	53		$	4,586		$	96
													Three months ended						Six months ended
	March 31, 2014		Unpaid				Recorded			Allowance for			Average			Interest			Average			Interest
			Principal				Investment			Loan Losses			Recorded			Income			Recorded			Income
			Balance							Allocated			Investment			Recognized			Investment			Recognized
	With no related allowance recorded:
	Single family		$	2,499			$	2,334		$	—		$	2,467		$	4		$	2,111		$	10
	Multifamily		3,366				3,011			—			3,022			36			3,706			73
	Commercial real estate		2,134				2,062			—			1,966			13			1,870			28
	Construction and land development		—				—			—			—			—			—			—
	Commercial business		—				—			—			—			—			—			—
	Consumer and other		335				117			—			118			—			127			—
	With an allowance recorded:
	Single family		1,235				408			99			204			—			510			—
	Multifamily		—				—			—			85			—			114			—
	Commercial real estate		—				—			—			99			—			126			—
	Construction and land development		—				—			—			—			—			64			—
	Commercial business		—				—			—			—			—			—			—
	Consumer and other		60				60			60			60			1			60			2
			$	9,629			$	7,992		$	159		$	8,021		$	54		$	8,688		$	113
Schedule of loans modified in a TDR, by class
Schedule of Loans and Leases Receivable, Related Parties	An analysis of such loans is as follows:
		Six Months Ended March 31, 2015
	Balance, beginning	$	4,653
	New loans originated	1,159
	Draws on lines of credit	131
	Principal repayments	(610		)
	Balance, ending	$	5,333
Past due loans
Loans
Schedule of recorded investment by accrual status	The following table presents the recorded investment in nonaccrual loans by class of loans as of March 31, 2015 and September 30, 2014:
		31-Mar-15				September 30,
						2014
	Single family	$	426			$	791
	Multifamily	—				—
	Commercial real estate	394				350
	Construction and land development	—				—
	Commercial business	—				22
	Consumer and other:
	Home equity lines of credit	194				145
	Education	74				120
	Other	—				2
		$	1,088			$	1,430
Troubled debt restructurings
Loans
Schedule of recorded investment by accrual status	The following is a summary of troubled debt restructured loans (TDRs) at March 31, 2015 and September 30, 2014:
		March 31, 2015				September 30, 2014
	Troubled debt restructurings - accrual	$	3,449			$	3,507
	Troubled debt restructurings - nonaccrual	—				195
		$	3,449			$	3,702

Deposits_Tables

Deposits (Tables)	6 Months Ended
	Mar. 31, 2015
Deposits [Abstract]
Schedule of composition of deposits	The following table presents the composition of deposits as of:
		March 31, 2015				30-Sep-14
		Amount		Percent		Amount		Percent
	Checking Accounts:
	Noninterest bearing	$	86,814	16.95	%	$	77,790	17.1	%
	Interest bearing	138,605		27.07	%	132,925		29.22	%
		225,419		44.02	%	210,715		46.32	%
	Passbook and Statement Savings	127,028		24.81	%	122,227		26.87	%
	Variable Rate Money Market Accounts	46,752		9.13	%	25,615		5.63	%
	Certificates of Deposit	112,848		22.04	%	96,371		21.18	%
		$	512,047	100	%	$	454,928	100	%

Regulatory_Capital_Tables

Regulatory Capital (Tables)	6 Months Ended
	Mar. 31, 2015
Regulatory Capital Requirements [Abstract]
Schedule of actual capital amounts and ratios and those required by the above regulatory standards	The Bank’s actual capital amounts and ratios and those required by the regulatory standards in effect as of the dates presented are as follows:
	At March 31, 2015	Actual						For Capital Adequacy				To Be Well Capitalized Under Prompt Corrective Action Provisions
								Purposes
		Amount			Ratio			Amount		Ratio		Amount		Ratio
	CETI capital (to risk-weighted assets) - Westbury Bank	64,023			13.18	%		21,859		4.5	%	31,574		6.5	%
	Tier 1 capital (to risk-weighted assets) - Westbury Bank	64,023			13.18	%		29,146		6	%	38,861		8	%
	Total capital (to risk-weighted assets) - Westbury Bank	$	68,506		14.11	%		$	38,841	8	%	$	48,551	10	%
	Leverage (to adjusted total assets) - Westbury Bank	64,023			10.57	%		24,228		4	%	30,285		5	%
	At September 30, 2014	Actual						For Capital Adequacy				To Be Well Capitalized Under Prompt Corrective Action Provisions
								Purposes
		Amount			Ratio			Amount		Ratio		Amount		Ratio
	Total capital (to risk-weighted assets) - Westbury Bank	$	65,181		16.18	%		$	32,228	8	%	$	40,285	10	%
	Tier 1 capital (to risk-weighted assets) - Westbury Bank	61,109			15.17	%		16,113		4	%	24,170		6	%
	Tier 1 capital (to adjusted total assets) - Westbury Bank	61,109			11.13	%		21,962		4	%	27,452		5	%
Schedule of reconciliation of the Bank's stockholders' equity to regulatory capital	The following table reconciles the Bank’s stockholders’ equity to regulatory capital as of March 31, 2015 and September 30, 2014:
		March 31,			September 30,
		2015			2014
	Stockholders’ equity of the Bank	$	69,299		$	67,529
	Less: Disallowed servicing assets	—			(162		)
	Unrealized (gain) loss on securities	(438		)	33
	Disallowed investment in subsidiary	(3,296		)	(3,296		)
	Disallowed deferred tax assets	(1,542		)	(2,995		)
	Tier 1 capital and tangible capital	64,023			61,109
	Plus: Allowable general valuation allowances	4,483			4,072
	Risk-based capital	$	68,506		$	65,181

Commitments_Tables

Commitments (Tables)	6 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of financial instruments whose contract amounts represent credit risk	The following instruments were outstanding whose contract amounts represent credit risk:
		31-Mar-15		September 30,
				2014
	Commitments to extend mortgage credit:
	Fixed rate	$	2,422	$	960
	Adjustable rate	1,941		3,339
	Unused commercial loan and home equity lines of credit	85,711		61,325
	Standby letters of credit	951		422
	Commitment to sell loans	1,594		326

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	6 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of assets and liabilities measured at fair value on a recurring basis	The following table summarizes assets measured at fair value on a recurring basis, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value as of:
						Fair Value Measurements
	31-Mar-15		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Securities available-for-sale
	U.S. Government and agency securities		$	25		$	—		$	25		$	—
	U.S. Government agency residential mortgage-backed securities		39,184			—			39,184			—
	U.S. Government agency collateralized mortgage obligations		2,400			—			2,400			—
	U.S. Government agency commercial mortgage-backed securities		9,694			—			9,694			—
	Municipal securities		26,578			—			26,578			—
	Total securities available-for-sale		$	77,881		$	—		$	77,881		$	—
	Derivatives		$	151		$	—		$	151		$	—
	Liabilities
	Derivatives		$	151		$	—		$	151		$	—
						Fair Value Measurements
	September 30, 2014		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets  for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Securities available-for-sale
	U.S. Government and agency securities		$	5,179		$	—		$	5,179		$	—
	U.S. Government agency residential mortgage-backed securities		37,196			—			37,196			—
	U.S. Government agency collateralized mortgage obligations		3,432			—			3,432			—
	U.S. Government agency commercial mortgage-backed securities		10,752			—			10,752			—
	Municipal securities		33,787			—			33,787			—
	Total securities available-for-sale		$	90,346		$	—		$	90,346		$	—
	Derivatives		$	87		$	—		$	87		$	—
	Liabilities
	Derivatives		$	87		$	—		$	87		$	—
Schedule of assets measured at fair value on a nonrecurring basis
						Fair Value Measurements
	31-Mar-15		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Impaired loans		$	276		$	—		$	—		$	276
	Foreclosed real estate		2,100			—			—			2,100
	Mortgage servicing rights		1,409			—			—			1,409
						Fair Value Measurements
	September 30, 2014		Total			Quoted Prices in			Significant Other			Significant Other
						Active Markets for			Observable Inputs			Unobservable
						Identical Assets			(Level 2)			Inputs (Level 3)
						(Level 1)
	Assets
	Impaired loans		$	405		$	—		$	—		$	405
	Foreclosed real estate		2,355			—			—			2,355
	Mortgage servicing rights		1,624			—			—			1,624
Schedule of estimated fair values and related carrying amounts of the entity's financial instruments	The estimated fair values and related carrying amounts of the Company’s financial instruments are as follows:
		31-Mar-15
		Carrying			Estimated Fair			Quoted Prices in			Significant Other			Significant Other
		Amount			Value			Active Markets for			Observable			Unobservable
								Identical Assets			Inputs			Inputs
								(Level 1)			(Level 2)			(Level 3)
	Financial assets:
	Cash and cash equivalents	$	16,805		$	16,805		$	16,805		$	—		$	—
	Securities available for sale	77,881			77,881			—			77,881			—
	Securities held to maturity	3,025			3,042			—			3,042			—
	Loans, net	467,447			467,980			—			—			467,980
	Loans held for sale, net	1,594			1,594			—			1,594			—
	Federal Home Loan Bank stock	3,350			3,350			—			—			3,350
	Mortgage servicing rights	1,409			1,409			—			—			1,409
	Accrued interest receivable	1,930			1,930			1,930			—			—
	Derivative asset	151			151			—			151			—
	Financial liabilities:
	Deposits	512,047			489,066			86,814			—			402,252
	Advances from Federal Home Loan Bank	13,000			13,000			—			13,000			—
	Advance payments by borrowers for property taxes and insurance	1,966			1,966			1,966			—			—
	Accrued interest payable	4			4			4			—			—
	Derivative liability	151			151			—			151			—
		30-Sep-14
		Carrying			Estimated Fair			Quoted Prices in			Significant Other			Significant Other
		Amount			Value			Active Markets for			Observable			Unobservable
								Identical Assets			Inputs			Inputs
								(Level 1)			(Level 2)			(Level 3)
	Financial assets:
	Cash and cash equivalents	$	17,608		$	17,608		$	17,608		$	—		$	—
	Securities available for sale	90,346			90,346			—			90,346			—
	Loans, net	416,874			415,857			—			—			415,857
	Loans held for sale, net	326			326			—			326			—
	Federal Home Loan Bank stock	2,670			2,670			—			—			2,670
	Mortgage servicing rights	1,624			1,624			—			—			1,624
	Accrued interest receivable	1,784			1,784			1,784			—			—
	Derivative asset	87			87			—			87			—
	Financial liabilities:
	Deposits	454,928			442,342			77,790			—			364,552
	Advances from Federal Home Loan Bank	17,000			17,000			—			17,000			—
	Advance payments by borrowers for property taxes and insurance	5,869			5,869			5,869			—			—
	Accrued interest payable	3			3			3			—			—
	Derivative liability	87			87			—			87			—

Compensation_Equity_Plans_Tabl

Compensation Equity Plans (Tables)	6 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Allocation of Share-based Compensation Costs by Plan	The following table summarizes the impact of the Company's share-based payment plans in the financial statements for the periods shown:
		Three Months Ended March 31,							Six Months Ended March 31,
		2015				2014			2015		2014
	Total cost of stock grant plan during the year	$	155			$	—		$	310	$	—
	Total cost of stock option plan during the year	46				—			92		—
	Total cost of share-based payment plans during the year	$	201			$	—		$	402	—
	Amount of related income tax benefit recognized in income	$	79			$	—		$	158	$	—
Schedule of Stock Options Activity	The following table summarizes stock options outstanding for the three and six months ended March 31, 2015:
		Number of Options		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
	Options outstanding as of December 31, 2014	326,224		$	15.2
	Granted	—		—
	Exercised	—		—
	Expired or canceled	—		—
	Forfeited	—		—
	Options outstanding as of March 31, 2015	326,224		$	15.2		9.25	$	750
	Options exercisable as of March 31, 2015	—		$	—		—	$	—
		Number of Options		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
	Options outstanding as of September 30, 2014	326,224		$	15.2
	Granted	—		—
	Exercised	—		—
	Expired or canceled	—		—
	Forfeited	—		—
	Options outstanding as of March 31, 2015	326,224		$	15.2		9.25	$	750
	Options exercisable as of March 31, 2015	—		$	—		—	$	—
Schedule of Stock Options Valuation Assumptions	The following assumptions were used for options granted during the year ended September 30, 2014:
	Risk-free interest rate	2.1		%
	Expected volatility of Company's stock	9.49		%
	Expected dividend yield	—		%
	Expected life of options (years)	7.5
	Weighted average fair value per option of options granted during the year	$	2.82
Schedule of Restricted Stock Units Award Activity	The following is a summary of changes in restricted shares for the three and six months ended March 31, 2015:
		Number of Shares			Weighted Average Grant Date Fair Value
	Shares Outstanding at December 31, 2014	203,665			$	15.2
	Granted	—			—
	Vested	—			—
	Forfeited	—			—
	Shares Outstanding at March 31, 2015	203,665			$	15.2
		Number of Shares			Weighted Average Grant Date Fair Value
	Shares Outstanding at September 30, 2014	203,665			$	15.2
	Granted	—			—
	Vested	—			—
	Forfeited	—			—
	Shares Outstanding at March 31, 2015	203,665			$	15.2

Condensed_Parent_Company_Finan1

Condensed Parent Company Financial Information (Tables)	6 Months Ended
	Mar. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheet	The condensed financial statements of Westbury Bancorp, Inc. (parent company only) are presented below:
	Balance Sheets
	(In thousands)
		March 31,			September 30,
		2015			2014
	Assets
	Cash and interest bearing deposits	$	2,775		$	6,878
	Investments	1,424			6,590
	Loan to ESOP	3,778			3,931
	Investment in subsidiary	72,702			71,131
	Other assets	1,992			1,674
	Total assets	$	82,671		$	90,204
	Liabilities and Stockholders' Equity
	Total liabilities	$	131		$	115
	Stockholders' equity	82,540			90,089
	Total liabilities and stockholders' equity	$	82,671		$	90,204
Condensed Income Statement
	Statements of Operations
	(In thousands)
		Three Months Ended March 31,						Six Months Ended March 31,
		2015			2014			2015			2014
	Interest and other income	$	63		$	71		$	126		$	141
	Interest and other expense	165			261			349			448
	Loss before income tax benefit and equity in undistributed net income of subsidiary	(102		)	(190		)	(223		)	(307		)
	Income tax benefit	(24		)	(61		)	(54		)	(93		)
	Loss before equity in undistributed net income (loss) of subsidiary	(78		)	(129		)	(169		)	(214		)
	Equity in undistributed net income (loss) of subsidiary	562			(1,670		)	1,100			(1,517		)
	Net income (loss)	$	484		$	(1,799	)	$	931		$	(1,731	)
Condensed Cash Flow Statement
	Statements of Cash Flows
	(in thousands)
		For Six Months Ended March 31,
		2015			2014
	Cash Flows From Operating Activities
	Net income (loss)	$	931		$	(1,731	)
	Adjustments to reconcile net income (loss) to net cash used in operating activities:
	Equity in undistributed net income (loss) of subsidiary	(1,100		)	1,517
	Net change in other liabilities	16			6
	Net change in other assets	100			47
	Net cash used in operating activities	(53		)	(161		)
	Cash Flows From Investing Activities
	Purchase of securities	(728		)	(663		)
	Sales and maturities of securities	5,894			706
	Payments received on ESOP loan	153			183
	Net cash provided by investing activities	5,319			226
	Cash Flows From Financing Activities
	Repurchase of common stock	(9,369		)	—
	Net cash used in financing activities	(9,369		)	—
	Net increase (decrease) in cash	(4,103		)	65
	Cash
	Beginning of period	6,878			9,271
	End of period	$	2,775		$	9,336

Earnings_Per_Share_Details

Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income (loss)	$484	($1,799)	$931	($1,731)
Basic potential common shares:
Weighted average shares outstanding (in shares)	4,657,638	5,142,541	4,746,438	5,142,541
Weighted average unallocated ESOP shares (in shares)	-368,549	-387,405	-371,149	-390,262
Basic weighted average shares outstanding (in shares)	4,289,089	4,755,136	4,375,289	4,752,279
Dilutive potential common shares (in shares)	33,670	0	28,971	0
Diluted weighted average shares outstanding (in shares)	4,322,759	4,755,136	4,404,260	4,752,279
Basic loss per share (in dollars per share)	$0.11	($0.38)	$0.21	($0.36)
Diluted loss per share (in dollars per share)	$0.11	($0.38)	$0.21	($0.36)

Investment_Securitites_Details

Investment Securitites (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Securities Available for Sale
Amortized Cost	$77,155	$90,422
Gross Unrealized Gains	913	710
Gross Unrealized (Losses)	-187	-786
Fair Value	77,881	90,346
Held-to-maturity Securities [Abstract]
Amortized Cost	3,025	0
Fair Value	3,042
Total Investment Securities
Amortized Cost	80,180	90,422
Gross Unrealized Gains	930	710
Gross Unrealized (Losses)	-187	-786
Fair Value	80,923	90,346
U.S. Government and agency securities
Securities Available for Sale
Amortized Cost	24	5,250
Gross Unrealized Gains	1	0
Gross Unrealized (Losses)	0	-71
Fair Value	25	5,179
U.S. Government agency residential mortgage-backed securities
Securities Available for Sale
Amortized Cost	38,762	37,144
Gross Unrealized Gains	534	389
Gross Unrealized (Losses)	-112	-337
Fair Value	39,184	37,196
U.S. Government agency collateralized mortgage obligations
Securities Available for Sale
Amortized Cost	2,424	3,458
Gross Unrealized Gains	23	30
Gross Unrealized (Losses)	-47	-56
Fair Value	2,400	3,432
U.S. Government agency commercial mortgage-backed securities
Securities Available for Sale
Amortized Cost	9,617	10,835
Gross Unrealized Gains	77	11
Gross Unrealized (Losses)	0	-94
Fair Value	9,694	10,752
Municipal securities
Securities Available for Sale
Amortized Cost	26,328	33,735
Gross Unrealized Gains	278	280
Gross Unrealized (Losses)	-28	-228
Fair Value	26,578	33,787
Held-to-maturity Securities [Abstract]
Amortized Cost	3,025	0
Gross Unrealized Gains	17	0
Gross Unrealized (Losses)	0	0
Fair Value	$3,042	$0

Investment_Securitites_Details1

Investment Securitites (Details 2) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
Available for Sale, Amortized Cost
Due in one year or less	$2,447,000		$2,447,000
Due after one year through five years	14,696,000		14,696,000
Due after five years through ten years	7,604,000		7,604,000
Due after ten years	1,605,000		1,605,000
Total	77,155,000		77,155,000
Available for Sale, Fair Value
Due in one year or less	2,475,000		2,475,000
Due after one year through five years	14,865,000		14,865,000
Due after five years through ten years	7,671,000		7,671,000
Due after ten years	1,592,000		1,592,000
Fair Value	77,881,000		77,881,000		90,346,000
Other disclosures
Proceeds from sales of securities available-for-sale	5,452,000	14,145,000	17,536,000	14,145,000
Gross realized gains on the sale of securities available-for-sale	14,000	170,000	125,000	170,000
Gross realized losses on the sale of securities available-for-sale	11,000	146,000	52,000	146,000
Securities pledged to secure treasury, tax, and loan deposits and other purposes	0		0		0
Held to maturity, Amortized Cost
Due in one year or less	566,000		566,000
Due after one year through five years	679,000		679,000
Due after five years through ten years	929,000		929,000
Due after five years through ten years	851,000		851,000
Amortized Cost	3,025,000		3,025,000		0
Amortized Cost	80,180,000		80,180,000		90,422,000
Held to maturity, Fair Value
Due in one year or less	566,000		566,000
Due after one year through five years	680,000		680,000
Due after five years through ten years	937,000		937,000
Due after ten years	859,000		859,000
Fair Value	3,042,000		3,042,000
Investment Securities	80,923,000		80,923,000		90,346,000
U.S. Government agency collateralized mortgage obligations
Available for Sale, Amortized Cost
U.S. Government agency securities	2,424,000		2,424,000
Available for Sale, Fair Value
U.S. Government agency securities	2,400,000		2,400,000
Fair Value	2,400,000		2,400,000		3,432,000
U.S. Government agency residential mortgage-backed securities
Available for Sale, Amortized Cost
U.S. Government agency securities	38,762,000		38,762,000
Available for Sale, Fair Value
U.S. Government agency securities	39,184,000		39,184,000
Fair Value	39,184,000		39,184,000		37,196,000
U.S. Government agency commercial mortgage-backed securities
Available for Sale, Amortized Cost
U.S. Government agency securities	9,617,000		9,617,000
Available for Sale, Fair Value
U.S. Government agency securities	9,694,000		9,694,000
Fair Value	$9,694,000		$9,694,000		$10,752,000

Investment_Securitites_Details2

Investment Securitites (Details 3) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified	security	security
Total temporary impaired securities
Less than 12 months, Fair Value	$5,866	$18,898
Less than 12 months, Unrealized Losses	-26	-135
12 months or longer, Fair Value	10,764	33,799
12 months or longer, Unrealized Losses	-161	-651
Total, Fair Value	16,630	52,697
Total, Unrealized Losses	-187	-786
Number of securities in an unrealized loss position, greater than twelve months	17	63
Number of securities in an unrealized loss position, less than twelve months	8	25
U.S. Government and agency securities
Total temporary impaired securities
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	0	5,179
12 months or longer, Unrealized Losses	0	-71
Total, Fair Value	0	5,179
Total, Unrealized Losses	0	-71
U.S. Government agency residential mortgage-backed securities
Total temporary impaired securities
Less than 12 months, Fair Value	3,858	9,617
Less than 12 months, Unrealized Losses	-13	-54
12 months or longer, Fair Value	8,321	13,075
12 months or longer, Unrealized Losses	-99	-283
Total, Fair Value	12,179	22,692
Total, Unrealized Losses	-112	-337
U.S. Government agency collateralized mortgage obligations
Total temporary impaired securities
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	753	891
12 months or longer, Unrealized Losses	-47	-56
Total, Fair Value	753	891
Total, Unrealized Losses	-47	-56
U.S. Government agency commercial mortgage-backed securities
Total temporary impaired securities
Less than 12 months, Fair Value	0	6,235
Less than 12 months, Unrealized Losses	0	-73
12 months or longer, Fair Value	0	1,033
12 months or longer, Unrealized Losses	0	-21
Total, Fair Value	0	7,268
Total, Unrealized Losses	0	-94
Municipal securities
Total temporary impaired securities
Less than 12 months, Fair Value	2,008	3,046
Less than 12 months, Unrealized Losses	-13	-8
12 months or longer, Fair Value	1,690	13,621
12 months or longer, Unrealized Losses	-15	-220
Total, Fair Value	3,698	16,667
Total, Unrealized Losses	($28)	($228)

Loans_Details

Loans (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Loans
Loans	$472,251		$421,181	$360,974
Less: Net deferred loan fees	321		235
Less: Allowance for loan losses	4,483	4,224	4,072	3,898	3,743	4,266
Net loans	467,447		416,874
Real Estate
Loans
Loans	418,358		363,216
Single family
Loans
Loans	150,102		135,337	131,981
Less: Allowance for loan losses	1,064	1,025	1,072	1,413	1,658	1,873
Multifamily
Loans
Loans	92,194		76,396	54,243
Less: Allowance for loan losses	1,025	932	757	107	138	165
Commercial real estate
Loans
Loans	155,121		135,121	121,579
Less: Allowance for loan losses	1,507	1,388	1,412	1,747	1,493	1,501
Construction and land development
Loans
Loans	20,941		16,362	12,280
Less: Allowance for loan losses	361	367	301	252	171	374
Commercial business
Loans
Loans	34,569		37,675	23,965
Less: Allowance for loan losses	415	412	454	279	220	211
Consumer
Loans
Loans	19,324		20,290	16,926
Less: Allowance for loan losses	111	100	76	100	63	142
Home equity lines of credit
Loans
Loans	12,608		14,275
Education
Loans
Loans	4,374		4,694
Other
Loans
Loans	$2,342		$1,321

Loans_Details_2

Loans (Details 2) (USD $)	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
Contractual aging of the recorded investment in past due loans
Current	$470,183,000	$417,836,000
Total Loans	472,251,000	421,181,000	360,974,000
Troubled debt restructurings - accrual	0	0
Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	1,088,000	1,430,000
Single family
Contractual aging of the recorded investment in past due loans
Current	148,804,000	133,102,000
Total Loans	150,102,000	135,337,000	131,981,000
Single family | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	426,000	791,000
Multifamily
Contractual aging of the recorded investment in past due loans
Current	92,194,000	76,396,000
Total Loans	92,194,000	76,396,000	54,243,000
Multifamily | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	0	0
Construction and land development
Contractual aging of the recorded investment in past due loans
Current	20,941,000	16,362,000
Total Loans	20,941,000	16,362,000	12,280,000
Construction and land development | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	0	0
Commercial business
Contractual aging of the recorded investment in past due loans
Current	34,567,000	37,653,000
Total Loans	34,569,000	37,675,000	23,965,000
Commercial business | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	0	22,000
Home equity lines of credit
Contractual aging of the recorded investment in past due loans
Current	12,428,000	13,918,000
Total Loans	12,608,000	14,275,000
Home equity lines of credit | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	194,000	145,000
Commercial real estate
Contractual aging of the recorded investment in past due loans
Current	154,727,000	134,584,000
Total Loans	155,121,000	135,121,000	121,579,000
Commercial real estate | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	394,000	350,000
Education
Contractual aging of the recorded investment in past due loans
Current	4,180,000	4,502,000
Total Loans	4,374,000	4,694,000
Education | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	74,000	120,000
Other
Contractual aging of the recorded investment in past due loans
Current	2,342,000	1,319,000
Total Loans	2,342,000	1,321,000
Other | Past due loans
Contractual aging of the recorded investment in past due loans
Recorded investment in nonaccrual loans	0	2,000
Financing Receivables, 60 to 89 Days Past Due
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	66,000	369,000
Financing Receivables, 60 to 89 Days Past Due | Single family
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	162,000
Financing Receivables, 60 to 89 Days Past Due | Multifamily
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due | Construction and land development
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due | Commercial business
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due | Home equity lines of credit
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due | Commercial real estate
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	163,000
Financing Receivables, 60 to 89 Days Past Due | Education
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	66,000	44,000
Financing Receivables, 60 to 89 Days Past Due | Other
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	1,072,000	2,057,000
Financing Receivables, 30 to 59 Days Past Due | Single family
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	1,016,000	1,623,000
Financing Receivables, 30 to 59 Days Past Due | Multifamily
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due | Construction and land development
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due | Commercial business
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	2,000	0
Financing Receivables, 30 to 59 Days Past Due | Home equity lines of credit
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	228,000
Financing Receivables, 30 to 59 Days Past Due | Commercial real estate
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	178,000
Financing Receivables, 30 to 59 Days Past Due | Education
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	54,000	28,000
Financing Receivables, 30 to 59 Days Past Due | Other
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	930,000	919,000
Financing Receivables, Equal to Greater than 90 Days Past Due | Single family
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	282,000	450,000
Financing Receivables, Equal to Greater than 90 Days Past Due | Multifamily
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Construction and land development
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Commercial business
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	0	22,000
Financing Receivables, Equal to Greater than 90 Days Past Due | Home equity lines of credit
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	180,000	129,000
Financing Receivables, Equal to Greater than 90 Days Past Due | Commercial real estate
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	394,000	196,000
Financing Receivables, Equal to Greater than 90 Days Past Due | Education
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	74,000	120,000
Financing Receivables, Equal to Greater than 90 Days Past Due | Other
Contractual aging of the recorded investment in past due loans
Financing Receivable, Recorded Investment, Past Due	$0	$2,000

Loans_Details_3

Loans (Details 3) (USD $)	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Risk category of loans evaluated by internal asset classification
Total	$472,251	$421,181	$360,974
Single family
Risk category of loans evaluated by internal asset classification
Total	150,102	135,337	131,981
Multifamily
Risk category of loans evaluated by internal asset classification
Total	92,194	76,396	54,243
Commercial real estate
Risk category of loans evaluated by internal asset classification
Total	155,121	135,121	121,579
Construction and land development
Risk category of loans evaluated by internal asset classification
Total	20,941	16,362	12,280
Commercial business
Risk category of loans evaluated by internal asset classification
Total	34,569	37,675	23,965
Home equity lines of credit
Risk category of loans evaluated by internal asset classification
Total	12,608	14,275
Education
Risk category of loans evaluated by internal asset classification
Total	4,374	4,694
Other
Risk category of loans evaluated by internal asset classification
Total	2,342	1,321
Pass
Risk category of loans evaluated by internal asset classification
Total	455,875	402,832
Pass | Single family
Risk category of loans evaluated by internal asset classification
Total	147,649	132,067
Pass | Multifamily
Risk category of loans evaluated by internal asset classification
Total	88,915	73,876
Pass | Commercial real estate
Risk category of loans evaluated by internal asset classification
Total	148,027	126,319
Pass | Construction and land development
Risk category of loans evaluated by internal asset classification
Total	20,941	16,357
Pass | Commercial business
Risk category of loans evaluated by internal asset classification
Total	31,284	34,112
Pass | Home equity lines of credit
Risk category of loans evaluated by internal asset classification
Total	12,343	14,088
Pass | Education
Risk category of loans evaluated by internal asset classification
Total	4,374	4,694
Pass | Other
Risk category of loans evaluated by internal asset classification
Total	2,342	1,319
Watch
Risk category of loans evaluated by internal asset classification
Total	12,070	12,808
Watch | Single family
Risk category of loans evaluated by internal asset classification
Total	1,151	1,317
Watch | Multifamily
Risk category of loans evaluated by internal asset classification
Total	2,841	1,915
Watch | Commercial real estate
Risk category of loans evaluated by internal asset classification
Total	4,931	6,117
Watch | Construction and land development
Risk category of loans evaluated by internal asset classification
Total	0	0
Watch | Commercial business
Risk category of loans evaluated by internal asset classification
Total	3,147	3,459
Watch | Home equity lines of credit
Risk category of loans evaluated by internal asset classification
Total	0	0
Watch | Education
Risk category of loans evaluated by internal asset classification
Total	0	0
Watch | Other
Risk category of loans evaluated by internal asset classification
Total	0	0
Special Mention
Risk category of loans evaluated by internal asset classification
Total	1,399	1,421
Special Mention | Single family
Risk category of loans evaluated by internal asset classification
Total	0	118
Special Mention | Multifamily
Risk category of loans evaluated by internal asset classification
Total	438	445
Special Mention | Commercial real estate
Risk category of loans evaluated by internal asset classification
Total	961	858
Special Mention | Construction and land development
Risk category of loans evaluated by internal asset classification
Total	0	0
Special Mention | Commercial business
Risk category of loans evaluated by internal asset classification
Total	0	0
Special Mention | Home equity lines of credit
Risk category of loans evaluated by internal asset classification
Total	0	0
Special Mention | Education
Risk category of loans evaluated by internal asset classification
Total	0	0
Special Mention | Other
Risk category of loans evaluated by internal asset classification
Total	0	0
Substandard
Risk category of loans evaluated by internal asset classification
Total	2,907	4,120
Substandard | Single family
Risk category of loans evaluated by internal asset classification
Total	1,302	1,835
Substandard | Multifamily
Risk category of loans evaluated by internal asset classification
Total	0	160
Substandard | Commercial real estate
Risk category of loans evaluated by internal asset classification
Total	1,202	1,827
Substandard | Construction and land development
Risk category of loans evaluated by internal asset classification
Total	0	5
Substandard | Commercial business
Risk category of loans evaluated by internal asset classification
Total	138	104
Substandard | Home equity lines of credit
Risk category of loans evaluated by internal asset classification
Total	265	187
Substandard | Education
Risk category of loans evaluated by internal asset classification
Total	0	0
Substandard | Other
Risk category of loans evaluated by internal asset classification
Total	0	2
Doubtful
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Single family
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Multifamily
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Commercial real estate
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Construction and land development
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Commercial business
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Home equity lines of credit
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Education
Risk category of loans evaluated by internal asset classification
Total	0	0
Doubtful | Other
Risk category of loans evaluated by internal asset classification
Total	$0	$0

Loans_Details_4

Loans (Details 4) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
Allowance for loan losses
Balance, beginning	$4,224	$3,743	$4,072	$4,266
Provision for loan losses	300	200	650	350
Loans charge-off	-61	-147	-286	-861
Recoveries	20	102	47	143
Balance, ending	4,483	3,898	4,483	3,898
Period-ended amount allocated for:
Individually evaluated for impairment	97	159	97	159
Collectively evaluated for impairment	4,386	3,739	4,386	3,739
Ending Balance	4,483	3,898	4,483	3,898
Loans:
Individually evaluated for impairment	4,920	7,992	4,920	7,992
Collectively evaluated for impairment	467,331	352,982	467,331	352,982
Total Loans	472,251	360,974	472,251	360,974	421,181
Real Estate
Loans:
Total Loans	418,358		418,358		363,216
Single family
Allowance for loan losses
Balance, beginning	1,025	1,658	1,072	1,873
Provision for loan losses	86	-183	189	-117
Loans charge-off	-47	-146	-208	-442
Recoveries	0	84	11	99
Balance, ending	1,064	1,413	1,064	1,413
Period-ended amount allocated for:
Individually evaluated for impairment	40	99	40	99
Collectively evaluated for impairment	1,024	1,314	1,024	1,314
Ending Balance	1,064	1,413	1,064	1,413
Loans:
Individually evaluated for impairment	1,683	2,742	1,683	2,742
Collectively evaluated for impairment	148,419	129,239	148,419	129,239
Total Loans	150,102	131,981	150,102	131,981	135,337
Multifamily
Allowance for loan losses
Balance, beginning	932	138	757	165
Provision for loan losses	93	-35	268	-62
Loans charge-off	0	0	0	0
Recoveries	0	4	0	4
Balance, ending	1,025	107	1,025	107
Period-ended amount allocated for:
Individually evaluated for impairment	0	0	0	0
Collectively evaluated for impairment	1,025	107	1,025	107
Ending Balance	1,025	107	1,025	107
Loans:
Individually evaluated for impairment	1,874	3,011	1,874	3,011
Collectively evaluated for impairment	90,320	51,232	90,320	51,232
Total Loans	92,194	54,243	92,194	54,243	76,396
Commercial real estate
Allowance for loan losses
Balance, beginning	1,388	1,493	1,412	1,501
Provision for loan losses	124	253	139	466
Loans charge-off	-14	0	-62	-232
Recoveries	9	1	18	12
Balance, ending	1,507	1,747	1,507	1,747
Period-ended amount allocated for:
Individually evaluated for impairment	0	0	0	0
Collectively evaluated for impairment	1,507	1,747	1,507	1,747
Ending Balance	1,507	1,747	1,507	1,747
Loans:
Individually evaluated for impairment	1,085	2,062	1,085	2,062
Collectively evaluated for impairment	154,036	119,517	154,036	119,517
Total Loans	155,121	121,579	155,121	121,579	135,121
Construction and land development
Allowance for loan losses
Balance, beginning	367	171	301	374
Provision for loan losses	-6	81	60	-122
Loans charge-off	0	0	0	0
Recoveries	0	0	0	0
Balance, ending	361	252	361	252
Period-ended amount allocated for:
Individually evaluated for impairment	0	0	0	0
Collectively evaluated for impairment	361	252	361	252
Ending Balance	361	252	361	252
Loans:
Individually evaluated for impairment	0	0	0	0
Collectively evaluated for impairment	20,941	12,280	20,941	12,280
Total Loans	20,941	12,280	20,941	12,280	16,362
Commercial business
Allowance for loan losses
Balance, beginning	412	220	454	211
Provision for loan losses	-2	48	-36	202
Loans charge-off	0	0	-14	-159
Recoveries	5	11	11	25
Balance, ending	415	279	415	279
Period-ended amount allocated for:
Individually evaluated for impairment	0	0	0	0
Collectively evaluated for impairment	415	279	415	279
Ending Balance	415	279	415	279
Loans:
Individually evaluated for impairment	0	0	0	0
Collectively evaluated for impairment	34,569	23,965	34,569	23,965
Total Loans	34,569	23,965	34,569	23,965	37,675
Consumer and other
Allowance for loan losses
Balance, beginning	100	63	76	142
Provision for loan losses	5	36	30	-17
Loans charge-off	0	-1	-2	-28
Recoveries	6	2	7	3
Balance, ending	111	100	111	100
Period-ended amount allocated for:
Individually evaluated for impairment	57	60	57	60
Collectively evaluated for impairment	54	40	54	40
Ending Balance	111	100	111	100
Loans:
Individually evaluated for impairment	278	177	278	177
Collectively evaluated for impairment	19,046	16,749	19,046	16,749
Total Loans	$19,324	$16,926	$19,324	$16,926	$20,290

Loans_Details_5

Loans (Details 5) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Unpaid Principal Balance
Total	$5,392	$9,629	$5,392	$9,629
Recorded Investment
Total	4,920	7,992	4,920	7,992
Allowance for Loan Losses Allocated
With an allowance recorded	97	159	97	159
Average Recorded Investment
Total	4,639	8,021	4,586	8,688
Interest Income Recognized
Total	53	54	96	113
Single family
Unpaid Principal Balance
With no related allowance recorded	1,569	2,499	1,569	2,499
With an allowance recorded	316	1,235	316	1,235
Recorded Investment
With no related allowance recorded	1,367	2,334	1,367	2,334
With an allowance recorded	316	408	316	408
Allowance for Loan Losses Allocated
With an allowance recorded	40	99	40	99
Average Recorded Investment
With no related allowance recorded	1,258	2,467	1,310	2,111
With an allowance recorded	355	204	343	510
Interest Income Recognized
With no related allowance	12	4	21	10
With related allowance	4	0	7	0
Multifamily
Unpaid Principal Balance
With no related allowance recorded	1,970	3,366	1,970	3,366
With an allowance recorded	0	0	0	0
Recorded Investment
With no related allowance recorded	1,874	3,011	1,874	3,011
With an allowance recorded	0	0	0	0
Allowance for Loan Losses Allocated
With an allowance recorded	0	0	0	0
Average Recorded Investment
With no related allowance recorded	1,884	3,022	1,894	3,706
With an allowance recorded	0	85	0	114
Interest Income Recognized
With no related allowance	20	36	40	73
With related allowance	0	0	0	0
Commercial real estate
Unpaid Principal Balance
With no related allowance recorded	1,179	2,134	1,179	2,134
With an allowance recorded	0	0	0	0
Recorded Investment
With no related allowance recorded	1,085	2,062	1,085	2,062
With an allowance recorded	0	0	0	0
Allowance for Loan Losses Allocated
With an allowance recorded	0	0	0	0
Average Recorded Investment
With no related allowance recorded	822	1,966	703	1,870
With an allowance recorded	0	99	55	126
Interest Income Recognized
With no related allowance	15	13	25	28
With related allowance	0	0	0	0
Construction and land development
Unpaid Principal Balance
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Recorded Investment
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Allowance for Loan Losses Allocated
With an allowance recorded	0	0	0	0
Average Recorded Investment
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	64
Interest Income Recognized
With no related allowance	0	0	0	0
With related allowance	0	0	0	0
Commercial business
Unpaid Principal Balance
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Recorded Investment
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Allowance for Loan Losses Allocated
With an allowance recorded	0	0	0	0
Average Recorded Investment
With no related allowance recorded	0	0	0	0
With an allowance recorded	0	0	0	0
Interest Income Recognized
With no related allowance	0	0	0	0
With related allowance	0	0	0	0
Consumer and other
Unpaid Principal Balance
With no related allowance recorded	301	335	301	335
With an allowance recorded	57	60	57	60
Recorded Investment
With no related allowance recorded	221	117	221	117
With an allowance recorded	57	60	57	60
Allowance for Loan Losses Allocated
With an allowance recorded	57	60	57	60
Average Recorded Investment
With no related allowance recorded	262	118	223	127
With an allowance recorded	58	60	58	60
Interest Income Recognized
With no related allowance	1	0	2	0
With related allowance	$1	$1	$1	$2

Loans_Details_6

Loans (Details 6) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
	contract	contract	contract	contract
Troubled debt restructured loans
Troubled debt restructurings - accrual	$0		$0		$0
Modified Trouble Debt Restructurings
Number of Modifications	0	0	0	1
Unpaid Principal Balance (at end of period)	0	0	0	88,000
Loans Modified in a Trouble Debt Restructuring [Abstract]
Other				88,000
Total	0	0	0	88,000
Number of re-defaults of TDR	0	0	0	0
Past due loans
Troubled debt restructured loans
Troubled debt restructurings - accrual	3,449,000		3,449,000		3,507,000
Troubled debt restructurings - nonaccrual	0		0		195,000
Troubled debt restructurings	$3,449,000		$3,449,000		$3,702,000

Loans_Loans_Details_7

Loans Loans (Details 7) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Loans and Leases Receivable, Related Parties [Roll Forward]
Loans outstanding to officers, employees, directors, and their associates	$5,333	$4,653
Loans and Leases Receivable, Related Parties, Additions	1,159
Loans and Leases Receivable, Related Parties, Amount Drawn Upon During Period	131
Loans and Leases Receivable, Related Parties, Collections	($610)

Deposits_Details

Deposits (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Negotiable order for withdrawal accounts:
Noninterest bearing	$86,814	$77,790
Interest bearing	138,605	132,925
Gross total	225,419	210,715
Passbook and Statement Savings	127,028	122,227
Variable Rate Money Market Accounts	46,752	25,615
Certificates of Deposit	112,848	96,371
Deposits	512,047	454,928
Negotiable order for withdrawal accounts:
Noninterest bearing (as a percent)	16.95%	17.10%
Interest bearing (as a percent)	27.07%	29.22%
Gross total (as a percent)	44.02%	46.32%
Passbook and Statement Savings (as a percent)	24.81%	26.87%
Variable Rate Money Market Accounts (as a percent)	9.13%	5.63%
Certificates of Deposit (as a percent)	22.04%	21.18%
Deposits (as a percent)	100.00%	100.00%
Certificates of Deposit over one hundred thousand dollars	55,170	34,853
Certificates of Deposit over two hundred fifty thousand dollars	$7,265	$5,602

Regulatory_Capital_Details

Regulatory Capital (Details) (Westbury Bank, USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Westbury Bank
Total capital (to risk-weighted assets), Amount
Actual	$68,506	$65,181
For Capital Adequacy Purposes	38,841	32,228
To be Well Capitalized Under Prompt Corrective Action Provisions	48,551	40,285
Total capital (to risk-weighted assets), Ratio
Actual (as a percent)	14.11%	16.18%
For Capital Adequacy Purposes (as a percent)	8.00%	8.00%
To be Well Capitalized Under Prompt Corrective Action Provisions (as a percent)	10.00%	10.00%
Tier 1 capital (to risk-weighted assets), Amount
Actual	64,023	61,109
For Capital Adequacy Purposes	29,146	16,113
To be Well Capitalized Under Prompt Corrective Action Provisions	38,861	24,170
Tier 1 capital (to risk-weighted assets), Ratio
Actual (as a percent)	13.18%	15.17%
For Capital Adequacy Purposes (as a percent)	6.00%	4.00%
To be Well Capitalized Under Prompt Corrective Action Provisions (as a percent)	8.00%	6.00%
CETI capital (to risk-weighted assets), Amount
Actual	64,023
For Capital Adequacy Purposes	21,859
To Be Well Capitalized Under Prompt Corrective Action Provisions	31,574
CETI capital (to risk-weighted assets), Ratio
Actual (as a percent)	13.18%
For Capital Adequacy Purposes (as a percent)	4.50%
To Be Well Capitalized Under Prompt Corrective Action Provisions (as a percent)	6.50%
Tier 1 capital (to adjusted total assets), Amount
Actual	64,023	61,109
For Capital Adequacy Purposes	24,228	21,962
To be Well Capitalized Under Prompt Corrective Action Provisions	$30,285	$27,452
Tier 1 capital (to adjusted total assets), Ratio
Actual (as a percent)	10.57%	11.13%
For Capital Adequacy Purposes (as a percent)	4.00%	4.00%
To be Well Capitalized Under Prompt Corrective Action Provisions (as a percent)	5.00%	5.00%

Regulatory_Capital_Stockholder

Regulatory Capital- Stockholders' equity of the Bank (Details) (USD $)	6 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013
Regulatory Capital
Stockholders' equity	$79,136	$86,487	$89,600	$90,602
Less: Disallowed servicing assets	-1,409	-1,624
Westbury Bank
Regulatory Capital
Stockholders' equity	69,299	67,529
Less: Disallowed servicing assets	0	-162
Unrealized (gain) loss on securities	-438	33
Investment in subsidiary	3,296	3,296
Disallowed deferred tax assets	-1,542	-2,995
Tier 1 and tangible capital	64,023	61,109
Plus: Allowable general valuation allowances	4,483	4,072
Actual	$68,506	$65,181

Commitments_Details

Commitments (Details) (USD $)	6 Months Ended
	Mar. 31, 2015	Sep. 30, 2014
Financial Instruments with Off-Balance Sheet Risk
Liabilities recorded for company's potential obligations	$0	$0
Fixed rate commitments to extend mortgage credit
Financial Instruments with Off-Balance Sheet Risk
Financial instruments whose contract amounts represent credit risk	2,422,000	960,000
Adjustable rate commitments to extend mortgage credit
Financial Instruments with Off-Balance Sheet Risk
Financial instruments whose contract amounts represent credit risk	1,941,000	3,339,000
Unused commercial loan and home equity lines of credit
Financial Instruments with Off-Balance Sheet Risk
Financial instruments whose contract amounts represent credit risk	85,711,000	61,325,000
Standby letters of credit
Financial Instruments with Off-Balance Sheet Risk
Financial instruments whose contract amounts represent credit risk	951,000	422,000
Maximum period of letters of credit primarily issued to support public and private borrowing arrangements	1 year
Commitment to sell loans
Financial Instruments with Off-Balance Sheet Risk
Financial instruments whose contract amounts represent credit risk	$1,594,000	$326,000

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Assets
Securities available-for-sale	$77,881	$90,346
U.S. Government and agency securities
Assets
Securities available-for-sale	25	5,179
U.S. Government agency residential mortgage-backed securities
Assets
Securities available-for-sale	39,184	37,196
U.S. Government agency collateralized mortgage obligations
Assets
Securities available-for-sale	2,400	3,432
U.S. Government agency commercial mortgage-backed securities
Assets
Securities available-for-sale	9,694	10,752
Municipal securities
Assets
Securities available-for-sale	26,578	33,787
Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities
Derivatives	0	0
Significant Other Observable Inputs (Level 2)
Assets and liabilities measured at fair value
Period of U.S. Treasury rate	10 years
Assets
Securities available-for-sale	77,881	90,346
Derivatives	151	87
Liabilities
Derivatives	151	87
Significant Other Unobservable Inputs (Level 3)
Liabilities
Derivatives	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Securities available-for-sale	0	0
Derivatives	0	0
Liabilities
Derivatives	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government and agency securities
Assets
Securities available-for-sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government agency residential mortgage-backed securities
Assets
Securities available-for-sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government agency collateralized mortgage obligations
Assets
Securities available-for-sale	0	0
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Securities available-for-sale	77,881	90,346
Derivatives	151	87
Liabilities
Derivatives	151	87
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government and agency securities
Assets
Securities available-for-sale	25	5,179
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government agency residential mortgage-backed securities
Assets
Securities available-for-sale	39,184	37,196
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government agency collateralized mortgage obligations
Assets
Securities available-for-sale	2,400	3,432
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government agency commercial mortgage-backed securities
Assets
Securities available-for-sale	9,694	10,752
Recurring basis | Significant Other Observable Inputs (Level 2) | Municipal securities
Assets
Securities available-for-sale	26,578	33,787
Recurring basis | Significant Other Unobservable Inputs (Level 3)
Assets
Securities available-for-sale	0	0
Derivatives	0	0
Liabilities
Derivatives	0	0
Recurring basis | Significant Other Unobservable Inputs (Level 3) | U.S. Government and agency securities
Assets
Securities available-for-sale	0	0
Recurring basis | Significant Other Unobservable Inputs (Level 3) | U.S. Government agency residential mortgage-backed securities
Assets
Securities available-for-sale	0	0
Recurring basis | Significant Other Unobservable Inputs (Level 3) | U.S. Government agency collateralized mortgage obligations
Assets
Securities available-for-sale	0	0
Total
Assets
Securities available-for-sale	77,881	90,346
Derivatives	151	87
Liabilities
Derivatives	151	87
Total | U.S. Government and agency securities
Assets
Securities available-for-sale		5,179
Total | U.S. Government agency residential mortgage-backed securities
Assets
Securities available-for-sale		37,196
Total | U.S. Government agency collateralized mortgage obligations
Assets
Securities available-for-sale		3,432
Total | U.S. Government agency commercial mortgage-backed securities
Assets
Securities available-for-sale		10,752
Total | Municipal securities
Assets
Securities available-for-sale		33,787
Total | Recurring basis
Assets
Securities available-for-sale	77,881
Derivatives	151
Liabilities
Derivatives	151
Total | Recurring basis | U.S. Government and agency securities
Assets
Securities available-for-sale	25
Total | Recurring basis | U.S. Government agency residential mortgage-backed securities
Assets
Securities available-for-sale	39,184
Total | Recurring basis | U.S. Government agency collateralized mortgage obligations
Assets
Securities available-for-sale	2,400
Total | Recurring basis | U.S. Government agency commercial mortgage-backed securities
Assets
Securities available-for-sale	9,694
Total | Recurring basis | Municipal securities
Assets
Securities available-for-sale	$26,578

Fair_Value_Measurements_Detail1

Fair Value Measurements (Details 2) (USD $)	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Assets measured at fair value on a nonrecurring basis
Impaired loans, valuation allowance	$97		$159
Foreclosed real estate	2,100	2,355
Significant Other Unobservable Inputs (Level 3)
Assets measured at fair value on a nonrecurring basis
Mortgage servicing rights	1,409	1,624
Carrying Amount
Assets measured at fair value on a nonrecurring basis
Mortgage servicing rights	1,409	1,624
Total
Assets measured at fair value on a nonrecurring basis
Mortgage servicing rights	1,409	1,624
Nonrecurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets measured at fair value on a nonrecurring basis
Impaired loans	0	0
Foreclosed real estate	0	0
Mortgage servicing rights	0	0
Nonrecurring Basis | Significant Other Observable Inputs (Level 2)
Assets measured at fair value on a nonrecurring basis
Impaired loans	0	0
Foreclosed real estate	0	0
Mortgage servicing rights	0	0
Nonrecurring Basis | Significant Other Unobservable Inputs (Level 3)
Assets measured at fair value on a nonrecurring basis
Impaired loans, valuation allowance	97	136
Mortgage servicing rights, valuation allowance	160	160
Impaired loans	276	405
Foreclosed real estate	2,100	2,355
Mortgage servicing rights	1,409	1,624
Nonrecurring Basis | Carrying Amount | Significant Other Unobservable Inputs (Level 3)
Assets measured at fair value on a nonrecurring basis
Impaired loans	373	541
Mortgage servicing rights	1,569	1,784
Nonrecurring Basis | Total
Assets measured at fair value on a nonrecurring basis
Impaired loans	276	405
Foreclosed real estate	2,100	2,355
Mortgage servicing rights	$1,409	$1,624

Fair_Value_Measurements_Detail2

Fair Value Measurements (Details 3) (USD $)	Mar. 31, 2015	Sep. 30, 2014
In Thousands, unless otherwise specified
Financial assets:
Securities available-for-sale	$77,881	$90,346
Securities held to maturity	3,025	0
Federal Home Loan Bank stock	3,350	2,670
Financial liabilities:
Advance payments by borrowers for property taxes and insurance	1,966	5,869
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	16,805	17,608
Securities held to maturity	0
Accrued interest receivable	1,930	1,784
Financial liabilities:
Deposits	86,814	77,790
Advances from Federal Home Loan Bank	0	0
Advance payments by borrowers for property taxes and insurance	1,966	5,869
Accrued interest payable	4	3
Derivative liability	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Securities available-for-sale	77,881	90,346
Securities held to maturity	3,042
Loans held for sale, net	1,594	326
Derivative asset	151	87
Financial liabilities:
Deposits	0	0
Advances from Federal Home Loan Bank	13,000	17,000
Advance payments by borrowers for property taxes and insurance	0	0
Accrued interest payable	0	0
Derivative liability	151	87
Significant Other Unobservable Inputs (Level 3)
Financial assets:
Securities held to maturity	0
Loans, net	467,980	415,857
Federal Home Loan Bank stock	3,350	2,670
Mortgage servicing rights	1,409	1,624
Financial liabilities:
Deposits	402,252	364,552
Advances from Federal Home Loan Bank	0	0
Advance payments by borrowers for property taxes and insurance	0	0
Accrued interest payable	0	0
Derivative liability	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	16,805	17,608
Securities available-for-sale	77,881	90,346
Securities held to maturity	3,025
Loans, net	467,447	416,874
Loans held for sale, net	1,594	326
Federal Home Loan Bank stock	3,350	2,670
Mortgage servicing rights	1,409	1,624
Accrued interest receivable	1,930	1,784
Derivative asset	151	87
Financial liabilities:
Deposits	512,047	454,928
Advances from Federal Home Loan Bank	13,000	17,000
Advance payments by borrowers for property taxes and insurance	1,966	5,869
Accrued interest payable	4	3
Derivative liability	151	87
Estimated Fair Value
Financial assets:
Cash and cash equivalents	16,805	17,608
Securities available-for-sale	77,881	90,346
Securities held to maturity	3,042
Loans, net	467,980	415,857
Loans held for sale, net	1,594	326
Federal Home Loan Bank stock	3,350	2,670
Mortgage servicing rights	1,409	1,624
Accrued interest receivable	1,930	1,784
Derivative asset	151	87
Financial liabilities:
Deposits	489,066	442,342
Advances from Federal Home Loan Bank	13,000	17,000
Advance payments by borrowers for property taxes and insurance	1,966	5,869
Accrued interest payable	4	3
Derivative liability	$151	$87

Employee_Stock_Ownership_Plan_

Employee Stock Ownership Plan (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014	Apr. 11, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee Stock Ownership Plan (ESOP), Debt Structure, Indirect Loan, Amount						$4,100,000
employee stock ownership plan, price per share						$10
ESOP committed-to-be-released shares, during period	5,142		10,284
ESOP compensation expense	86,000	72,000	198,000	168,000
Allocated shares to active participants	36,442		36,442		20,570
Shares committed to be released	5,142		5,142		15,428
Unallocated shares	365,121		365,121		375,405
Total ESOP shares	406,705		406,705		411,403	411,403
Fair value of unallocated shares	$6,390,000		$6,390,000		$5,650,000

Compensation_Equity_Plans_Cost

Compensation Equity Plans Cost of Share-based Payment Plans (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total cost of stock grant plan during the year	$155	$0	$310	$0
Total cost of stock option plan during the year	46	0	92	0
Total cost of share-based payment plans during the year	201	0	402	0
Amount of related income tax benefit recognized in income	$79	$0	$158	$0

Compensation_Equity_Plans_Stoc

Compensation Equity Plans Stock Option Activity (Details) (USD $)	3 Months Ended	6 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2015
Number of Options
Options outstanding as of September 30, 2014	326,224	326,224
Granted	0	0
Exercised	0	0
Expired or canceled	0	0
Forfeited	0	0
Options outstanding as of March 31, 2015	326,224	326,224
Options exercisable as of March 31, 2015	0	0
Weighted Average Exercise Price
Options outstanding as of September 30, 2014 (in dollars per share)	$15.20	$15.20
Granted (in dollars per share)	$0	$0
Exercised (in dollars per share)	$0	$0
Expired or canceled (in dollars per share)	$0	$0
Forfeited (in dollars per share)	$0	$0
Options outstanding as of March 31, 2015 (in dollars per share)	$15.20	$15.20
Options exercisable as of March 31, 2015 (in dollars per share)	$0	$0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Contractual Term	9 years 3 months	9 years 3 months
Outstanding, Aggregate Intrinsic Value	$750	$750
Options Exercisable, Aggregate Intrinsic Value	$0	$0

Compensation_Equity_Plans_Assu

Compensation Equity Plans Assumptions (Details) (USD $)	6 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.10%
Expected volatility of Company's stock	9.49%
Expected dividend yield	0.00%
Expected life of options (years)	7 years 6 months
Weighted average fair value per option of options granted during the year	$2.82

Compensation_Equity_Plans_Rest

Compensation Equity Plans Restricted Shares (Details) (Restricted Shares and Units, USD $)	3 Months Ended	6 Months Ended
	Mar. 31, 2015	Mar. 31, 2015
Restricted Shares and Units
Number of Shares
Shares Outstanding at September 30, 2014	203,665	203,665
Granted	0	0
Vested	0	0
Forfeited	0	0
Shares Outstanding at March 31, 2015	203,665	203,665
Weighted Average Grant Date Fair Value
Shares Outstanding at September 30, 2014 (in dollars per share)	$15.20	$15.20
Granted (in dollars per share)	$0	$0
Vested (in dollars per share)	$0	$0
Forfeited (in dollars per share)	$0	$0
Shares Outstanding at March 31, 2015 (in dollars per share)	$15.20	$15.20

Compensation_Equity_Plans_Narr

Compensation Equity Plans Narrative (Details) (USD $)	6 Months Ended
	Mar. 31, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, minimum	5 years
Vesting period, maximum	10 years
Restricted share vesting period	5 years
Intrinsic value of options exercised during the period	$0
Compensation cost not yet recognized	3,400,000
Period for recognition	4 years 3 months
Restricted Shares and Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of restricted shares vested during the period	$0
Westbury Bancorp Inc 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized		509,162
Westbury Bancorp Inc 2014 Equity Incentive Plan | Restricted Shares and Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized		203,665
Number of shares available for grant-stock grants	0
Westbury Bancorp Inc 2014 Equity Incentive Plan | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant-stock options	182,938

Condensed_Parent_Company_Finan2

Condensed Parent Company Financial Information Balance Sheet (Details) (USD $)	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and interest bearing deposits	$16,805	$17,608	$48,913	$47,665
Other assets	3,618	3,504
Total assets	610,134	568,695
Other liabilities	3,985	4,411
Stockholders' equity	79,136	86,487	89,600	90,602
Total liabilities and stockholders' equity	610,134	568,695
Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and interest bearing deposits	2,775	6,878
Investments	1,424	6,590
Loan to ESOP	3,778	3,931
Investment in subsidiary	72,702	71,131
Other assets	1,992	1,674
Total assets	82,671	90,204
Other liabilities	131	115
Stockholders' equity	82,540	90,089
Total liabilities and stockholders' equity	$82,671	$90,204

Condensed_Parent_Company_Finan3

Condensed Parent Company Financial Information Statements of Operations (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Condensed Income Statements, Captions [Line Items]
Net income (loss)	$484	($1,799)	$931	($1,731)
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest and other income	63	71	126	141
Interest and other expense	165	261	349	448
Loss before income tax benefit and equity in undistributed net income of subsidiary	-102	-190	-223	-307
Income tax benefit	-24	-61	-54	-93
Loss before equity in undistributed net income (loss) of subsidiary	-78	-129	-169	-214
Equity in undistributed net income (loss) of subsidiary	562	-1,670	1,100	-1,517
Net income (loss)	$484	($1,799)	$931	($1,731)

Condensed_Parent_Company_Finan4

Condensed Parent Company Financial Information Statement of Cash Flows (Details) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income (loss)	$931	($1,731)
Net change in other assets	-107	-312
Net cash used in operating activities	-2,385	-4,046
Net Cash Provided by (Used in) Investing Activities [Abstract]
Purchase of securities	-10,287	-9,599
Net cash provided by investing activities	-42,168	-5,106
Net Cash Provided by (Used in) Financing Activities [Abstract]
Purchase of Company treasury stock	-9,369	0
Net cash used in financing activities	43,750	10,400
Parent Company
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income (loss)	931	-1,731
Equity in undistributed net income (loss) of subsidiary	-1,100	1,517
Net change in other liabilities	16	6
Net change in other assets	100	47
Net cash used in operating activities	-53	-161
Net Cash Provided by (Used in) Investing Activities [Abstract]
Purchase of securities	-728	-663
Sales and maturities of securities	5,894	706
Payments received on ESOP loan	153	183
Net cash provided by investing activities	5,319	226
Net Cash Provided by (Used in) Financing Activities [Abstract]
Purchase of Company treasury stock	-9,369	0
Net cash used in financing activities	-9,369	0
Net increase (decrease) in cash	-4,103	65
Beginning of period	6,878	9,271
End of period	$2,775	$9,336