Credit Quality Assessment (Summary Information on Allowance for Loan and Lease Loss Activity) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Credit Quality Assessment [Abstract]
Balance at beginning of year			$ 37,802	$ 38,766	$ 38,766
Provision (credit) for loan and lease losses	$ 1,706	$ (192)	3,521	(1,016)
Loan and lease charge-offs			(2,753)	(1,541)
Loan and lease recoveries			1,091	1,365	1,886
Net charge-offs			(1,662)	(176)	(801)
Balance at period end	$ 39,661	$ 37,574	$ 39,661	$ 37,574	$ 37,802