Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Loan and lease loss	$ 5,984	$ 6,012
Deferred compensation	2,541	2,483
Actuarial adjustments on retirement benefits	7,714	8,525
State net operating losses	2,725	1,986
Other-than-temporary impairments on equity securities	331	317
Alternative minimum tax credits	3,114	2,156
Net unrealized holding losses on securities available-for-sale and swaps	2,762	472
Other deferred tax assets	2,676	3,209
Gross deferred tax assets	27,847	25,160
Valuation allowance	(2,341)	(1,609)
Total deferred tax assets, net of valuation allowance	25,506	23,551
Deferred tax liabilities:
Mortgage servicing rights	2,302	2,066
Retirement plans	6,265	6,307
Intangible assets	3,543	2,460
Depreciation	1,401	347
Other deferred tax liabilities	2,430	2,192
Total deferred tax liabilities	15,941	13,372
Net deferred tax assets	$ 9,565	$ 10,179