Loans - Presentation of Age Analysis of Past-Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 14,172	$ 10,895
Current Loans	2,247,051	2,179,767
Total loans	2,261,223	2,190,662
30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,834	3,856
60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,231	1,289
Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	7,107	5,750
Commercial Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,697	897
Current Loans	991,350	942,034
Total loans	994,047	942,931
Commercial Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	30	195
Commercial Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	602
Commercial Loans [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,065	702
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		171
Current Loans	166,027	133,972
Total loans	166,027	134,143
Commercial Loans [Member] | Multifamily [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		171
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,781
Current Loans	407,906	409,979
Total loans	409,687	409,979
Commercial Loans [Member] | Nonresidential [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	102
Commercial Loans [Member] | Nonresidential [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,679
Commercial Loans [Member] | Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Loans	19,653	16,830
Total loans	19,653	16,830
Commercial Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Loans	127,388	141,686
Total loans	127,388	141,686
Commercial Loans [Member] | Secured [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	416	726
Current Loans	264,288	232,580
Total loans	264,704	233,306
Commercial Loans [Member] | Secured [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	30	195
Commercial Loans [Member] | Secured [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	386	531
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	500
Current Loans	6,088	6,987
Total loans	6,588	6,987
Commercial Loans [Member] | Unsecured [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	500
Residential Mortgage Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	7,839	6,491
Current Loans	975,696	964,199
Total loans	983,535	970,690
Residential Mortgage Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,530	2,139
Residential Mortgage Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,780	882
Residential Mortgage Loans [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,529	3,470
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Loans	44,636	43,435
Total loans	44,636	43,435
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	7,839	6,491
Current Loans	931,060	920,764
Total loans	938,899	927,255
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,530	2,139
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,780	882
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,529	3,470
Consumer Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,636	3,507
Current Loans	280,005	273,534
Total loans	283,641	277,041
Consumer Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,274	1,522
Consumer Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	849	407
Consumer Loans [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,513	1,578
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,808	2,100
Current Loans	180,814	183,561
Total loans	183,622	185,661
Consumer Loans [Member] | Home Equity [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	892	658
Consumer Loans [Member] | Home Equity [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	716	295
Consumer Loans [Member] | Home Equity [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,200	1,147
Consumer Loans [Member] | Automobile [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	372	526
Current Loans	86,689	78,160
Total loans	87,061	78,686
Consumer Loans [Member] | Automobile [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	179	283
Consumer Loans [Member] | Automobile [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	70	112
Consumer Loans [Member] | Automobile [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	123	131
Consumer Loans [Member] | Marine [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	105	145
Current Loans	960	1,061
Total loans	1,065	1,206
Consumer Loans [Member] | Marine [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	105	145
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	256	693
Current Loans	2,990	3,654
Total loans	3,246	4,347
Consumer Loans [Member] | Recreational Vehicle [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	131	548
Consumer Loans [Member] | Recreational Vehicle [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	58
Consumer Loans [Member] | Recreational Vehicle [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	67	145
Consumer Loans [Member] | Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	95	43
Current Loans	8,552	7,098
Total loans	8,647	7,141
Consumer Loans [Member] | Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	72	33
Consumer Loans [Member] | Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	5
Consumer Loans [Member] | Other [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 18	$ 10