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		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Interest Expense - Subordinated Debentures [Member]	Jun. 30, 2013 Interest Expense - Subordinated Debentures [Member]	Jun. 30, 2014 Interest Expense - Subordinated Debentures [Member]	Jun. 30, 2013 Interest Expense - Subordinated Debentures [Member]	Jun. 30, 2014 Other Income [Member]	Jun. 30, 2013 Other Income [Member]	Jun. 30, 2014 Other Income [Member]	Jun. 30, 2013 Other Income [Member]	Jun. 30, 2014 Accrued Interest and Other Liabilities [Member]	Dec. 31, 2013 Accrued Interest and Other Liabilities [Member]
Derivative [Line Items]
Interest rate contracts													$ (1,089)	$ (1,116)
Interest rate contracts	17	245	(7)	319
Interest expense, Fair Value					(94)	(105)	(191)	(202)
Other income									$ 0	$ 0	$ 0	$ 0