Income Taxes - Summary of Deferred Tax Asset (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Employee benefit plans	$ 1,211	$ 1,177
Allowance for loan losses	1,306	1,294
Funded status of post-retirement benefits	(56)	(56)
Securities available for sale	(423)	(423)
Alternative minimum tax credit	462	462
Depreciation and amortization	179	86
Net deferred loan origination costs	(445)	(474)
Mortgage servicing rights	(1,738)	(1,025)
Net operating loss carryforward	2,682	2,571
Charitable contribution carryforward	988	84
Derivatives	(254)	(43)
Merger expenses		244
Other, net	(12)	1
Deferred tax assets (liabilities) before valuation allowances	3,900	3,898
Valuation allowance	$ (3,900)	$ (3,898)