Loans - Risk Category of Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 2,261,223	$ 2,190,662
Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,198,589	2,130,851
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	26,241	23,341
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	36,393	36,470
Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	36,393	36,470
Commercial Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	994,047	942,931
Commercial Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	938,839	890,320
Commercial Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	26,146	22,750
Commercial Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	29,062	29,861
Commercial Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	29,062	29,861
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	166,027	134,143
Commercial Loans [Member] | Multifamily [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	166,027	133,972
Commercial Loans [Member] | Multifamily [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		171
Commercial Loans [Member] | Multifamily [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		171
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	409,687	409,979
Commercial Loans [Member] | Nonresidential [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	380,838	378,160
Commercial Loans [Member] | Nonresidential [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,616	18,420
Commercial Loans [Member] | Nonresidential [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	12,233	13,399
Commercial Loans [Member] | Nonresidential [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	12,233	13,399
Commercial Loans [Member] | Land [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	19,653	16,830
Commercial Loans [Member] | Land [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	19,653	16,830
Commercial Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	127,388	141,686
Commercial Loans [Member] | Construction [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	125,003	139,540
Commercial Loans [Member] | Construction [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,385	2,146
Commercial Loans [Member] | Secured [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	264,704	233,306
Commercial Loans [Member] | Secured [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	240,812	214,924
Commercial Loans [Member] | Secured [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,145	2,184
Commercial Loans [Member] | Secured [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,747	16,198
Commercial Loans [Member] | Secured [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,747	16,198
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,588	6,987
Commercial Loans [Member] | Unsecured [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,506	6,894
Commercial Loans [Member] | Unsecured [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	82	93
Commercial Loans [Member] | Unsecured [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	82	93
Residential Mortgage Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	983,535	970,690
Residential Mortgage Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	977,806	965,129
Residential Mortgage Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	95	591
Residential Mortgage Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,634	4,970
Residential Mortgage Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,634	4,970
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	44,636	43,435
Residential Mortgage Loans [Member] | Construction [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	44,636	43,435
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	938,899	927,255
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	933,170	921,694
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	95	591
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,634	4,970
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,634	4,970
Consumer Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	283,641	277,041
Consumer Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	281,944	275,402
Consumer Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,697	1,639
Consumer Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,697	1,639
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	183,622	185,661
Consumer Loans [Member] | Home Equity [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	182,241	184,438
Consumer Loans [Member] | Home Equity [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,381	1,223
Consumer Loans [Member] | Home Equity [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,381	1,223
Consumer Loans [Member] | Auto [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	87,061	78,686
Consumer Loans [Member] | Auto [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	86,935	78,551
Consumer Loans [Member] | Auto [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	126	135
Consumer Loans [Member] | Auto [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	126	135
Consumer Loans [Member] | Marine [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,065	1,206
Consumer Loans [Member] | Marine [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	960	1,061
Consumer Loans [Member] | Marine [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	105	145
Consumer Loans [Member] | Marine [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	105	145
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,246	4,347
Consumer Loans [Member] | Recreational Vehicle [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,179	4,221
Consumer Loans [Member] | Recreational Vehicle [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	67	126
Consumer Loans [Member] | Recreational Vehicle [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	67	126
Consumer Loans [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,647	7,141
Consumer Loans [Member] | Other [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,629	7,131
Consumer Loans [Member] | Other [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	18	10
Consumer Loans [Member] | Other [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 18	$ 10