Credit Quality Assessment (Summary Information on Allowance for Loan and Lease Loss Activity) (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Summary Information On Allowance For Loan and Lease Loss Activity [Abstract]
Balance at beginning of year				$ 38,766,000				$ 42,957,000	$ 38,766,000	$ 42,957,000	$ 49,426,000
Provision (credit) for loan and lease losses	853,000	(192,000)	158,000	(982,000)	586,000	1,128,000	(2,876,000)	78,000	(163,000)	(1,084,000)	3,649,000
Loan and lease charge-offs									(2,687,000)	(11,165,000)	(12,804,000)
Loan and lease recoveries									1,886,000	8,058,000	2,686,000
Net charge-offs									(801,000)	(3,107,000)	(10,118,000)
Balance at period end	$ 37,802,000				$ 38,766,000				$ 37,802,000	$ 38,766,000	$ 42,957,000