Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Loan and lease loss	$ 6,012	$ 7,358
Deferred compensation	2,483	2,492
Actuarial adjustments on retirement benefits	8,525	8,625
State net operating losses	1,986	1,621
Other-than-temporary impairments on equity securities	317	577
Alternative minimum tax credits	2,156	1,067
Net unrealized holding losses on securities available-for-sale and swaps	472	0
Other	1,150	1,125
Gross deferred tax assets	23,101	22,865
Valuation allowance	(1,609)	(1,461)
Total deferred tax assets, net of valuation allowance	21,492	21,404
Deferred tax liabilities:
Market discount	2,481	2,224
Retirement plans	7,169	5,700
Intangible assets	1,663	2,308
Net unrealized holding gains on securities available-for-sale and swaps	0	837
Total deferred tax liabilities	11,313	11,069
Net deferred tax assets	$ 10,179	$ 10,335