Income Taxes - Schedule of Significant Components of Temporary Differences with Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Liabilities:
Net unrealized holding gains on securities available-for-sale	$ (3,563)	$ (3,783)
Prepaid pension	(2,865)	(3,472)
Deferred loan income	(2,847)	(2,165)
Purchase accounting adjustments	0	(631)
Depreciation on premises and equipment	(1,226)	(1,590)
Other	(809)	(812)
Total Deferred Tax liabilities	(11,310)	(12,453)
Deferred Tax Assets:
Allowance for loan losses	17,740	17,567
Purchase accounting adjustments	1,298	0
Other employee benefits	2,556	2,453
Low income housing partnerships	4,531	4,049
Net adjustment to funded status of pension	12,425	11,089
Impairment of securities	1,354	1,313
State net operating loss carryforwards	2,670	2,249
Other	6,155	4,668
Gross Deferred Tax Assets	48,729	43,388
Less: Valuation allowance	(2,670)	(2,249)
Total Deferred Tax Assets	46,059	41,139
Net Deferred Tax Asset	$ 34,749	$ 28,686