Derivative Instruments - 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, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Interest Expense - Subordinated Debentures [Member]	Sep. 30, 2013 Interest Expense - Subordinated Debentures [Member]	Sep. 30, 2014 Interest Expense - Subordinated Debentures [Member]	Sep. 30, 2013 Interest Expense - Subordinated Debentures [Member]	Sep. 30, 2014 Other Income [Member]	Sep. 30, 2013 Other Income [Member]	Sep. 30, 2014 Other Income [Member]	Sep. 30, 2013 Other Income [Member]	Sep. 30, 2014 Accrued Interest and Other Liabilities [Member]	Dec. 31, 2013 Accrued Interest and Other Liabilities [Member]
Derivative [Line Items]
Interest rate contracts													$ (936)	$ (1,116)
Interest rate contracts	99	8	(117)	327
Interest expense, Fair Value					(96)	(102)	(287)	(304)
Other income									$ 0	$ 0	$ 0	$ 0