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	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, January 1	$ 2,801	$ 2,798
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Other-than-temporary impairment loss included in earnings (loss)	0	0
Unrealized gain (loss) included in comprehensive income	(154)	3
Balance at September 30, 2015 and December 31, 2014	$ 2,647	$ 2,801