Loans - Presentation of Loans Individually Evaluated for Impairment by Class (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	$ 14,808	$ 13,831	$ 14,808	$ 13,831	$ 12,801
With no specific allowance recorded, Recorded Investment	8,941	7,962	8,941	7,962	6,499
With no specific allowance recorded, Average Recorded Investment	8,821	8,265	7,404	8,019
With no specific allowance recorded, Interest Income Recognized	27	67	120	165
With no specific allowance recorded, Cash Basis Income Recognized	27	51	110	132
With a specific allowance recorded, Unpaid Principal Balance	13,838	15,448	13,838	15,448	14,768
With a specific allowance recorded, Recorded Investment	12,754	14,835	12,754	14,835	14,095
With a specific allowance recorded, Allowance for Loan Losses Allocated	1,172	1,637	1,172	1,637	1,201
With a specific allowance recorded, Average Recorded Investment	14,599	15,025	14,746	16,459
With a specific allowance recorded, Interest Income Recognized	190	262	690	680
With a specific allowance recorded, Cash Basis Income Recognized	187	172	641	538
Total Unpaid Principal Balance	28,646	29,279	28,646	29,279	27,569
Total Recorded Investment	21,695	22,797	21,695	22,797	20,594
Total Average Recorded Investment	23,420	23,290	22,150	24,478
Total Interest Income Recognized	217	329	810	845
Total Cash Basis Income Recognized	214	223	751	670
Commercial Loans [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	7,584	4,739	7,584	4,739	4,758
With no specific allowance recorded, Recorded Investment	3,248	1,055	3,248	1,055	300
With no specific allowance recorded, Average Recorded Investment	3,025	1,050	1,619	1,019
With no specific allowance recorded, Interest Income Recognized	5	9	23	14
With no specific allowance recorded, Cash Basis Income Recognized	5	9	23	14
With a specific allowance recorded, Unpaid Principal Balance	2,263	2,457	2,263	2,457	2,175
With a specific allowance recorded, Recorded Investment	1,454	2,053	1,454	2,053	1,717
With a specific allowance recorded, Allowance for Loan Losses Allocated	234	514	234	514	103
With a specific allowance recorded, Average Recorded Investment	3,167	2,064	2,800	2,171
With a specific allowance recorded, Interest Income Recognized	48	13	186	65
With a specific allowance recorded, Cash Basis Income Recognized	46	13	189	65
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	152	25	152	25	443
With no specific allowance recorded, Recorded Investment					170
With no specific allowance recorded, Average Recorded Investment			43
With no specific allowance recorded, Interest Income Recognized			1
With no specific allowance recorded, Cash Basis Income Recognized			1
With a specific allowance recorded, Unpaid Principal Balance		422		422
With a specific allowance recorded, Recorded Investment		275		275
With a specific allowance recorded, Allowance for Loan Losses Allocated		28		28
With a specific allowance recorded, Average Recorded Investment		275		275
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	3,049	624	3,049	624	588
With no specific allowance recorded, Recorded Investment	2,895	134	2,895	134	130
With no specific allowance recorded, Average Recorded Investment	2,848	136	1,488	108
With no specific allowance recorded, Interest Income Recognized	3	1	20	5
With no specific allowance recorded, Cash Basis Income Recognized	3	1	20	5
With a specific allowance recorded, Unpaid Principal Balance	827	1,216	827	1,216	1,186
With a specific allowance recorded, Recorded Investment	827	1,210	827	1,210	1,186
With a specific allowance recorded, Allowance for Loan Losses Allocated	132	13	132	13	12
With a specific allowance recorded, Average Recorded Investment	414	1,221	1,183	1,320
With a specific allowance recorded, Interest Income Recognized	30	13	75	65
With a specific allowance recorded, Cash Basis Income Recognized	30	13	67	65
Commercial Loans [Member] | Land [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Average Recorded Investment				5
Commercial Loans [Member] | Construction [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	2,445	2,447	2,445	2,447	2,447
Commercial Loans [Member] | Secured [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	1,464	1,169	1,464	1,169	806
With no specific allowance recorded, Recorded Investment	353	921	353	921
With no specific allowance recorded, Average Recorded Investment	177	914	88	906
With no specific allowance recorded, Interest Income Recognized	2		2	1
With no specific allowance recorded, Cash Basis Income Recognized	2		2	1
With a specific allowance recorded, Unpaid Principal Balance	1,436	819	1,436	819	989
With a specific allowance recorded, Recorded Investment	627	568	627	568	531
With a specific allowance recorded, Allowance for Loan Losses Allocated	102	473	102	473	91
With a specific allowance recorded, Average Recorded Investment	2,753	568	1,617	576
With a specific allowance recorded, Interest Income Recognized	18		111
With a specific allowance recorded, Cash Basis Income Recognized	16		122
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	474	474	474	474	474
With no specific allowance recorded, Interest Income Recognized		8		8
With no specific allowance recorded, Cash Basis Income Recognized		8		8
Residential Mortgage Loans [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	5,349	6,578	5,349	6,578	5,840
With no specific allowance recorded, Recorded Investment	4,533	5,424	4,533	5,424	4,908
With no specific allowance recorded, Average Recorded Investment	4,663	5,709	4,637	5,558
With no specific allowance recorded, Interest Income Recognized	16	41	80	117
With no specific allowance recorded, Cash Basis Income Recognized	16	32	71	92
With a specific allowance recorded, Unpaid Principal Balance	7,541	8,455	7,541	8,455	8,298
With a specific allowance recorded, Recorded Investment	7,410	8,340	7,410	8,340	8,178
With a specific allowance recorded, Allowance for Loan Losses Allocated	653	817	653	817	798
With a specific allowance recorded, Average Recorded Investment	7,510	8,401	7,910	9,430
With a specific allowance recorded, Interest Income Recognized	90	147	329	378
With a specific allowance recorded, Cash Basis Income Recognized	89	98	291	291
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	5,349	6,578	5,349	6,578	5,840
With no specific allowance recorded, Recorded Investment	4,533	5,424	4,533	5,424	4,908
With no specific allowance recorded, Average Recorded Investment	4,663	5,709	4,637	5,558
With no specific allowance recorded, Interest Income Recognized	16	41	80	117
With no specific allowance recorded, Cash Basis Income Recognized	16	32	71	92
With a specific allowance recorded, Unpaid Principal Balance	7,541	8,455	7,541	8,455	8,298
With a specific allowance recorded, Recorded Investment	7,410	8,340	7,410	8,340	8,178
With a specific allowance recorded, Allowance for Loan Losses Allocated	653	817	653	817	798
With a specific allowance recorded, Average Recorded Investment	7,510	8,401	7,910	9,430
With a specific allowance recorded, Interest Income Recognized	90	147	329	378
With a specific allowance recorded, Cash Basis Income Recognized	89	98	291	291
Consumer Loans [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	1,875	2,514	1,875	2,514	2,203
With no specific allowance recorded, Recorded Investment	1,160	1,483	1,160	1,483	1,291
With no specific allowance recorded, Average Recorded Investment	1,133	1,506	1,148	1,442
With no specific allowance recorded, Interest Income Recognized	6	17	17	34
With no specific allowance recorded, Cash Basis Income Recognized	6	10	16	26
With a specific allowance recorded, Unpaid Principal Balance	4,034	4,536	4,034	4,536	4,295
With a specific allowance recorded, Recorded Investment	3,890	4,442	3,890	4,442	4,200
With a specific allowance recorded, Allowance for Loan Losses Allocated	285	306	285	306	300
With a specific allowance recorded, Average Recorded Investment	3,922	4,560	4,036	4,858
With a specific allowance recorded, Interest Income Recognized	52	102	175	237
With a specific allowance recorded, Cash Basis Income Recognized	52	61	161	182
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	1,003	1,262	1,003	1,262	1,084
With no specific allowance recorded, Recorded Investment	890	1,044	890	1,044	957
With no specific allowance recorded, Average Recorded Investment	908	1,134	906	1,076
With no specific allowance recorded, Interest Income Recognized	3	6	10	17
With no specific allowance recorded, Cash Basis Income Recognized	3	4	9	15
With a specific allowance recorded, Unpaid Principal Balance	3,545	4,156	3,545	4,156	3,925
With a specific allowance recorded, Recorded Investment	3,448	4,074	3,448	4,074	3,842
With a specific allowance recorded, Allowance for Loan Losses Allocated	268	289	268	289	283
With a specific allowance recorded, Average Recorded Investment	3,492	4,138	3,622	4,398
With a specific allowance recorded, Interest Income Recognized	45	92	155	215
With a specific allowance recorded, Cash Basis Income Recognized	45	56	142	165
Consumer Loans [Member] | Auto [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	140	26	140	26	25
With no specific allowance recorded, Recorded Investment	123	19	123	19	17
With no specific allowance recorded, Average Recorded Investment	74	21	45	29
With no specific allowance recorded, Interest Income Recognized	3	1	3	1
With no specific allowance recorded, Cash Basis Income Recognized	3	1	3	1
With a specific allowance recorded, Unpaid Principal Balance	2		2
With a specific allowance recorded, Recorded Investment	2		2
With a specific allowance recorded, Average Recorded Investment	1		1
Consumer Loans [Member] | Marine [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	354	553	354	553	502
With no specific allowance recorded, Recorded Investment	105	181	105	181	145
With no specific allowance recorded, Average Recorded Investment	105	181	115	181
With a specific allowance recorded, Unpaid Principal Balance	84	93	84	93	91
With a specific allowance recorded, Recorded Investment	84	93	84	93	91
With a specific allowance recorded, Allowance for Loan Losses Allocated	1		1		1
With a specific allowance recorded, Average Recorded Investment	85	94	88	96
With a specific allowance recorded, Interest Income Recognized	1	2	3	5
With a specific allowance recorded, Cash Basis Income Recognized	1	1	3	4
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	378	652	378	652	592
With no specific allowance recorded, Recorded Investment	42	218	42	218	172
With no specific allowance recorded, Average Recorded Investment	46	159	82	146
With no specific allowance recorded, Interest Income Recognized		9	4	15
With no specific allowance recorded, Cash Basis Income Recognized		4	4	9
With a specific allowance recorded, Unpaid Principal Balance	403	287	403	287	279
With a specific allowance recorded, Recorded Investment	356	275	356	275	267
With a specific allowance recorded, Allowance for Loan Losses Allocated	16	17	16	17	$ 16
With a specific allowance recorded, Average Recorded Investment	344	328	325	364
With a specific allowance recorded, Interest Income Recognized	6	8	17	17
With a specific allowance recorded, Cash Basis Income Recognized	$ 6	4	$ 16	13
Consumer Loans [Member] | Other [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance		21		21
With no specific allowance recorded, Recorded Investment		21		21
With no specific allowance recorded, Average Recorded Investment		11		10
With no specific allowance recorded, Interest Income Recognized		1		1
With no specific allowance recorded, Cash Basis Income Recognized		$ 1		$ 1