Fair Value - Reconciliation of All Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Accretion/(amortization) of discount or premium	$ 11	$ 11
Credit loss write-downs		(161)
Fair Value, Inputs, Level 3 [Member] | Pooled Trust Preferred Securities Available - For -Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	9,359	7,327
Accretion/(amortization) of discount or premium	9	8
Sales/ payments received	(1,403)	(43)
Credit loss write-downs		(161)
Increase/(decrease) in fair value of securities	1,187	1,329
Ending balance	9,152	8,460
Fair Value, Inputs, Level 3 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	984	1,306
Accretion/(amortization) of discount or premium	2	3
Matured securities	(310)	(320)
Credit loss write-downs
Ending balance	$ 676	$ 989