Loans - Presentation of Age Analysis of Past-Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 16,657	$ 18,871
Current Loans	1,999,484	1,500,606
Total loans	2,016,141	1,519,477
30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	6,287	8,488
60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,750	2,525
Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	8,620	7,858
Commercial Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,731	3,967
Current Loans	820,885	500,291
Total loans	822,616	504,258
Commercial Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	134	3,511
Commercial Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	4
Commercial Loans [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,593	456
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	275
Current Loans	120,205	93,597
Total loans	120,480	93,597
Commercial Loans [Member] | Multifamily [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	275
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,219	3,572
Current Loans	380,392	227,829
Total loans	381,611	231,401
Commercial Loans [Member] | Nonresidential [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	20	3,511
Commercial Loans [Member] | Nonresidential [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,199	61
Commercial Loans [Member] | Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	9	34
Current Loans	15,153	8,339
Total loans	15,162	8,373
Commercial Loans [Member] | Land [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	9	34
Commercial Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Loans	116,863	68,158
Total loans	116,863	68,158
Commercial Loans [Member] | Secured [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	228	361
Current Loans	177,766	94,982
Total loans	177,994	95,343
Commercial Loans [Member] | Secured [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	114
Commercial Loans [Member] | Secured [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	4
Commercial Loans [Member] | Secured [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	110	361
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Loans	10,506	7,386
Total loans	10,506	7,386
Residential Mortgage Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	11,031	10,952
Current Loans	909,000	787,669
Total loans	920,031	798,621
Residential Mortgage Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	4,704	3,774
Residential Mortgage Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,523	1,717
Residential Mortgage Loans [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	4,804	5,461
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Loans	49,092	35,695
Total loans	49,092	35,695
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	11,031	10,952
Current Loans	859,908	751,974
Total loans	870,939	762,926
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	4,704	3,774
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	1,523	1,717
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	4,804	5,461
Consumer Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,895	3,952
Current Loans	269,599	212,646
Total loans	273,494	216,598
Consumer Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,449	1,203
Consumer Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	223	808
Consumer Loans [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,223	1,941
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,097	3,068
Current Loans	192,755	161,986
Total loans	195,852	165,054
Consumer Loans [Member] | Home Equity [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,184	941
Consumer Loans [Member] | Home Equity [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	120	458
Consumer Loans [Member] | Home Equity [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,793	1,669
Consumer Loans [Member] | Automobile [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	369	133
Current Loans	63,995	39,476
Total loans	64,364	39,609
Consumer Loans [Member] | Automobile [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	187	130
Consumer Loans [Member] | Automobile [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	100
Consumer Loans [Member] | Automobile [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	82	3
Consumer Loans [Member] | Marine [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	181	267
Current Loans	1,345	1,529
Total loans	1,526	1,796
Consumer Loans [Member] | Marine [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	181	267
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	212	478
Current Loans	5,484	7,124
Total loans	5,696	7,602
Consumer Loans [Member] | Recreational Vehicle [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	47	131
Consumer Loans [Member] | Recreational Vehicle [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		347
Consumer Loans [Member] | Recreational Vehicle [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	165
Consumer Loans [Member] | Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	36	6
Current Loans	6,020	2,531
Total loans	6,056	2,537
Consumer Loans [Member] | Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	31	1
Consumer Loans [Member] | Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3	3
Consumer Loans [Member] | Other [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 2	$ 2