Income Taxes - Summary of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Allowance for credit losses/Allowance for loan losses	$ 21,300	$ 11,937
Stock based compensation plans	985	958
Purchase accounting fair market value adjustments	2,174	3,632
Non-accrued interest	664	381
Deferred compensation	2,570	2,444
Loss on equity securities	50	0
Other-than-temporary impairment loss on investment securities	0	41
Federal net operating loss carryforward	875	875
Unrealized loss on pension plans	13	2
Unrealized loss on derivatives	42	0
Other, net	508	594
Gross deferred tax assets	29,181	20,864
Deferred tax liabilities:
Core deposit intangible from acquired companies	852	1,235
Undistributed income from subsidiary not consolidated for tax return purposes (REIT)	852	678
Deferred loan costs	1,822	1,461
Depreciation and amortization	793	750
Prepaid expenses	578	443
Deferred gain on securities	0	162
Loss on equity securities	0	65
Unrealized gain on investment securities	4,746	884
Unrealized gains on hedging derivative	0	80
Other	260	301
Gross deferred tax liabilities	9,903	6,059
Net deferred tax assets	$ 19,278	$ 14,805