Reconciliation of Activity for Assets Measured at Fair Value based on Significant Unobservable (Non-market) Information (Detail) (Bank-Issued Trust Preferred Securities, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Bank-Issued Trust Preferred Securities
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, January 1	$ 2,801	$ 2,798
Transfers into Level 3
Transfers out of Level 3	0	0
Other-than-temporary impairment loss included in earnings	0	0
Unrealized gain included in comprehensive income	15	3
Balance at Sep 30, 2014 and December 31, 2013	$ 2,816	$ 2,801