Credit Quality Assessment (Summary Information on Allowance for Loan and Lease Loss Activity) (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Credit Quality Assessment [Abstract]
Balance at beginning of year	$ 37,802,000	$ 38,766,000	$ 38,766,000
Provision (credit) for loan and lease losses	597,000	(982,000)
Loan and lease charge-offs	(1,114,000)	(717,000)
Loan and lease recoveries	190,000	959,000	1,886,000
Net charge-offs	(924,000)	242,000	(801,000)
Balance at period end	$ 37,475,000	$ 38,026,000	$ 37,802,000