Income Taxes - Components of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Allowance for loan losses	$ 3,088	$ 2,840
Fair value adjustments – business combination	966	1,135
Deferred compensation	2,056	1,903
Net operating loss carryover	0	71
Post-retirement benefits	836	892
Unrealized loss on interest rate swap	42	34
Nonaccrual loan interest	589	390
Accrued expenses	1,254	699
Deferred fees and costs	588	598
Unrealized loss on securities available for sale	940	0
Other	366	344
Deferred tax assets	10,725	8,906
Deferred tax liabilities:
Unrealized gain on securities available for sale	0	126
Premises and equipment	1,459	1,413
Unrealized gain on trading securities	63	156
Intangibles – section 197	2,414	2,593
Mortgage servicing rights	314	291
Other	178	78
Deferred tax liabilities	4,428	4,657
Net deferred tax asset	$ 6,297	$ 4,249