Interest Rate Swaps - Amounts and Locations of Activity Related to Interest Rate Swaps Designated as Cash Flow Hedges within Corporation's Consolidated Balance Sheet and Statement of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Interest rate contracts	$ 137	$ 111	$ 409
Accrued interest payable and other liabilities [Member]
Derivative [Line Items]
Interest rate contract, fair value	(736)	(946)
Interest Expense - Subordinated Debentures [Member]
Derivative [Line Items]
Interest expense, Fair Value	(378)	(384)	(400)
Other Income [Member]
Derivative [Line Items]
Other income	$ 0	$ 0	$ 0