Loans - Risk Category of Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 1,884,701	$ 1,519,477
Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,831,785	1,485,074
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	18,711	13,126
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	34,205	21,277
Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	34,205	21,277
Commercial Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	742,255	504,258
Commercial Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	700,593	480,216
Commercial Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	17,932	13,021
Commercial Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	23,730	11,021
Commercial Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	23,730	11,021
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	121,565	93,597
Commercial Loans [Member] | Multifamily [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	117,375	89,468
Commercial Loans [Member] | Multifamily [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,482	3,564
Commercial Loans [Member] | Multifamily [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	708	565
Commercial Loans [Member] | Multifamily [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	708	565
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	342,300	231,401
Commercial Loans [Member] | Nonresidential [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	333,010	217,204
Commercial Loans [Member] | Nonresidential [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,208	6,037
Commercial Loans [Member] | Nonresidential [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,082	8,160
Commercial Loans [Member] | Nonresidential [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,082	8,160
Commercial Loans [Member] | Land [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,867	8,373
Commercial Loans [Member] | Land [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,858	8,339
Commercial Loans [Member] | Land [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9	34
Commercial Loans [Member] | Land [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9	34
Commercial Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	96,765	68,158
Commercial Loans [Member] | Construction [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	96,362	68,158
Commercial Loans [Member] | Construction [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	403
Commercial Loans [Member] | Secured [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	162,109	95,343
Commercial Loans [Member] | Secured [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	134,433	89,756
Commercial Loans [Member] | Secured [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,839	3,420
Commercial Loans [Member] | Secured [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,837	2,167
Commercial Loans [Member] | Secured [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,837	2,167
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,649	7,386
Commercial Loans [Member] | Unsecured [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,555	7,291
Commercial Loans [Member] | Unsecured [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	94	95
Commercial Loans [Member] | Unsecured [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	94	95
Residential Mortgage Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	891,295	798,621
Residential Mortgage Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	882,216	790,691
Residential Mortgage Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	779	104
Residential Mortgage Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,300	7,826
Residential Mortgage Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,300	7,826
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	56,946	35,695
Residential Mortgage Loans [Member] | Construction [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	56,946	35,695
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	834,349	762,926
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	825,270	754,996
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	779	104
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,300	7,826
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,300	7,826
Consumer Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	251,151	216,598
Consumer Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	248,976	214,167
Consumer Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1
Consumer Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,175	2,430
Consumer Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,175	2,430
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	187,762	165,054
Consumer Loans [Member] | Home Equity [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	186,055	163,101
Consumer Loans [Member] | Home Equity [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,707	1,953
Consumer Loans [Member] | Home Equity [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,707	1,953
Consumer Loans [Member] | Auto [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	50,389	39,609
Consumer Loans [Member] | Auto [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	50,258	39,577
Consumer Loans [Member] | Auto [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1
Consumer Loans [Member] | Auto [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	131	31
Consumer Loans [Member] | Auto [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	131	31
Consumer Loans [Member] | Marine [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,601	1,796
Consumer Loans [Member] | Marine [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,432	1,530
Consumer Loans [Member] | Marine [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	169	266
Consumer Loans [Member] | Marine [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	169	266
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,401	7,602
Consumer Loans [Member] | Recreational Vehicle [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,234	7,424
Consumer Loans [Member] | Recreational Vehicle [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	167	178
Consumer Loans [Member] | Recreational Vehicle [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	167	178
Consumer Loans [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,998	2,537
Consumer Loans [Member] | Other [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,997	2,535
Consumer Loans [Member] | Other [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1	2
Consumer Loans [Member] | Other [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 1	$ 2