Income Taxes - Summary of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for loan and lease losses	$ 10,662	$ 13,775
Stock based compensation plans	769	1,095
Purchase accounting fair market value adjustments	1,441	2,752
Non-accrued interest	394	730
Deferred compensation	2,007	2,648
Depreciation and amortization	805	1,486
Other-than-temporary impairment loss on investment securities	77	255
Unrealized losses on securities available for sale	1,108	292
Other, net	675	767
Gross deferred tax assets	17,938	23,800
Deferred tax liabilities:
Core deposit intangible from acquired companies	664	1,366
Undistributed income from subsidiary not consolidated for tax return purposes (REIT)	12,015	924
Deferred loan costs	1,169	1,545
Prepaid expenses	524	641
Deferred gain on securities	116	194
Unfunded pension benefits	7	18
Unrealized gains on hedging derivative	229	361
Other	357	841
Gross deferred tax liabilities	15,081	5,890
Net deferred tax assets	$ 2,857	$ 17,910