Income Taxes - Summary of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Allowance for loan and lease losses	$ 11,651	$ 10,662
Stock based compensation plans	865	769
Purchase accounting fair market value adjustments	1,192	1,441
Non-accrued interest	256	394
Deferred compensation	2,142	2,007
Depreciation and amortization	630	805
Other-than-temporary impairment loss on investment securities	59	77
Unrealized losses on securities available for sale	3,162	1,108
Other, net	585	675
Gross deferred tax assets	20,542	17,938
Deferred tax liabilities:
Core deposit intangible from acquired companies	516	664
Undistributed income from subsidiary not consolidated for tax return purposes (REIT)	149	12,015
Deferred loan costs	1,418	1,169
Prepaid expenses	459	524
Deferred gain on securities	166	116
Unfunded pension benefits	17	7
Loss on equity securities	36	0
Unrealized gains on hedging derivative	322	229
Other	270	357
Gross deferred tax liabilities	3,353	15,081
Net deferred tax assets	$ 17,189	$ 2,857