Loans Receivable, Net and Allowance for Loan Losses - Schedule of Investment and Unpaid Principal Balances for Impaired Loans (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Dec. 04, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Recorded Investment		$ 20,315		$ 20,315			$ 22,565
Unpaid Principal Balance	$ 3,468	23,854		23,854			27,215
Associated Allowance		485		485		$ 485	347
Average Recorded Investment		19,462	$ 26,622	20,677	$ 27,086
Interest	717	107	196	261	423
Contractual cash flows	4,185
Non-accretable discount	(1,973)
Expected cash flows	2,212
Accretable discount	(240)
Estimated fair value	$ 1,972
With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		17,773		17,773			19,994
Unpaid Principal Balance		20,957		20,957			24,488
Average Recorded Investment		16,740	22,165	17,991	23,225
Interest		105	190	255	411
With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		2,542		2,542			2,571
Unpaid Principal Balance		2,897		2,897			2,727
Associated Allowance		485		485			347
Average Recorded Investment		2,722	4,457	2,686	3,861
Interest		2	6	6	12
Residential Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		7,011		7,011			8,721
Unpaid Principal Balance		9,145		9,145			11,167
Associated Allowance		128		128			198
Average Recorded Investment		7,558	9,975	8,074	10,676
Interest		9	26	21	57
Residential Real Estate Loans [Member] | With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		5,351		5,351			6,721
Unpaid Principal Balance		7,155		7,155			9,016
Average Recorded Investment		5,573	7,296	6,049	8,040
Interest		9	22	21	48
Residential Real Estate Loans [Member] | With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		1,660		1,660			2,000
Unpaid Principal Balance		1,990		1,990			2,151
Associated Allowance		128		128			198
Average Recorded Investment		1,985	2,679	2,025	2,636
Interest			4		9
Commercial Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		10,542		10,542			11,237
Unpaid Principal Balance		11,697		11,697			13,231
Associated Allowance		26		26			36
Average Recorded Investment		9,559	13,618	10,235	13,882
Interest		67	131	172	307
Commercial Real Estate Loans [Member] | With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		10,422		10,422			10,939
Unpaid Principal Balance		11,569		11,569			12,928
Average Recorded Investment		9,218	12,128	9,890	12,908
Interest		67	131	172	307
Commercial Real Estate Loans [Member] | With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		120		120			298
Unpaid Principal Balance		128		128			303
Associated Allowance		26		26			36
Average Recorded Investment		341	1,490	345	974
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		1,742		1,742			1,698
Unpaid Principal Balance		1,826		1,826			1,725
Associated Allowance		125		125
Average Recorded Investment		1,737	1,925	1,724	1,354
Interest		29	37	62	52
Commercial Loans [Member] | With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		1,557		1,557			1,698
Unpaid Principal Balance		1,627		1,627			1,725
Average Recorded Investment		1,637	1,919	1,665	1,350
Interest		29	37	62	52
Commercial Loans [Member] | With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		185		185
Unpaid Principal Balance		199		199
Associated Allowance		125		125
Average Recorded Investment		100	6	59	4
Home Equity Loans and Lines of Credit [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		216		216			361
Unpaid Principal Balance		292		292			432
Associated Allowance		5		5
Average Recorded Investment		207	653	264	738
Interest					2
Home Equity Loans and Lines of Credit [Member] | With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		211		211			361
Unpaid Principal Balance		287		287			432
Average Recorded Investment		202	594	260	672
Interest					2
Home Equity Loans and Lines of Credit [Member] | With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		5		5
Unpaid Principal Balance		5		5
Associated Allowance		5		5
Average Recorded Investment		5	59	4	66
Auto Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		780		780			526
Unpaid Principal Balance		865		865			638
Associated Allowance		201		201			113
Average Recorded Investment		393	450	372	436
Interest		2	2	6	5
Auto Loans [Member] | With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		208		208			253
Unpaid Principal Balance		290		290			365
Average Recorded Investment		102	228	119	255
Interest					2
Auto Loans [Member] | With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		572		572			273
Unpaid Principal Balance		575		575			273
Associated Allowance		201		201			113
Average Recorded Investment		291	222	253	181
Interest		2	2	6	$ 3
Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		24		24			22
Unpaid Principal Balance		29		29			22
Average Recorded Investment		8	1	8
Other [Member] | With no Specific Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		24		24			22
Unpaid Principal Balance		29		29			$ 22
Average Recorded Investment		$ 8		$ 8
Other [Member] | With an Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment			$ 1