Loans - Risk Category of Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 1,850,364	$ 1,519,477
Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,797,757	1,485,074
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	19,375	13,126
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	33,232	21,277
Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	33,232	21,277
Commercial Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	708,364	504,258
Commercial Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	665,719	480,216
Commercial Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	19,118	13,021
Commercial Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	23,527	11,021
Commercial Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	23,527	11,021
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	108,330	93,597
Commercial Loans [Member] | Multifamily [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	104,037	89,468
Commercial Loans [Member] | Multifamily [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,524	3,564
Commercial Loans [Member] | Multifamily [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	769	565
Commercial Loans [Member] | Multifamily [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	769	565
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	325,633	231,401
Commercial Loans [Member] | Nonresidential [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	310,787	217,204
Commercial Loans [Member] | Nonresidential [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,873	6,037
Commercial Loans [Member] | Nonresidential [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,973	8,160
Commercial Loans [Member] | Nonresidential [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,973	8,160
Commercial Loans [Member] | Land [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,276	8,373
Commercial Loans [Member] | Land [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,267	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	94,727	68,158
Commercial Loans [Member] | Construction [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	94,727	68,158
Commercial Loans [Member] | Secured [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	161,945	95,343
Commercial Loans [Member] | Secured [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	138,543	89,756
Commercial Loans [Member] | Secured [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,721	3,420
Commercial Loans [Member] | Secured [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	15,681	2,167
Commercial Loans [Member] | Secured [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	15,681	2,167
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,453	7,386
Commercial Loans [Member] | Unsecured [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,358	7,291
Commercial Loans [Member] | Unsecured [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	95	95
Commercial Loans [Member] | Unsecured [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	95	95
Residential Mortgage Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	890,785	798,621
Residential Mortgage Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	883,336	790,691
Residential Mortgage Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	257	104
Residential Mortgage Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,192	7,826
Residential Mortgage Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,192	7,826
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	51,372	35,695
Residential Mortgage Loans [Member] | Construction [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	51,372	35,695
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	839,413	762,926
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	831,964	754,996
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	257	104
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,192	7,826
Residential Mortgage Loans [Member] | One-to Four-Family [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,192	7,826
Consumer Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	251,215	216,598
Consumer Loans [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	248,702	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	2,513	2,430
Consumer Loans [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,513	2,430
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	190,751	165,054
Consumer Loans [Member] | Home Equity [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	188,709	163,101
Consumer Loans [Member] | Home Equity [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,042	1,953
Consumer Loans [Member] | Home Equity [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,042	1,953
Consumer Loans [Member] | Auto [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	46,804	39,609
Consumer Loans [Member] | Auto [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	46,712	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	92	31
Consumer Loans [Member] | Auto [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	92	31
Consumer Loans [Member] | Marine [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,672	1,796
Consumer Loans [Member] | Marine [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,477	1,530
Consumer Loans [Member] | Marine [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	195	266
Consumer Loans [Member] | Marine [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	195	266
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,066	7,602
Consumer Loans [Member] | Recreational Vehicle [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,890	7,424
Consumer Loans [Member] | Recreational Vehicle [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	176	178
Consumer Loans [Member] | Recreational Vehicle [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	176	178
Consumer Loans [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,922	2,537
Consumer Loans [Member] | Other [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,914	2,535
Consumer Loans [Member] | Other [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8	2
Consumer Loans [Member] | Other [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 8	$ 2