Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan and lease losses	$ 7,680	$ 6,410
Deferred compensation	1,834	1,734
Actuarial adjustments on retirement benefits*	4,868	4,592
State net operating losses	5,071	4,730
Other-than-temporary impairments on equity securities	151	148
Net unrealized holding losses on securities available-for-sale and swaps	915	2,968
Lease liability	8,177
Other deferred tax assets	1,146	1,368
Gross deferred tax assets	29,842	21,950
Valuation allowance	(4,284)	(3,830)
Total deferred tax assets, net of valuation allowance	25,558	18,120
Deferred tax liabilities:
Mortgage servicing rights	1,404	1,463
Retirement plans	5,299	5,263
Deferred loan fees and costs	1,330	1,163
Acquisition-related fair value adjustments	1,515	1,605
Intangible assets	1,956	1,987
Accounting method change adjustment	768	1,154
Depreciation	1,137	937
Right of use asset	7,481
Other deferred tax liabilities	1,053	963
Total deferred tax liabilities	21,943	14,535
Net deferred tax assets	$ 3,615	$ 3,585