Credit Quality Assessment (Summary of Impaired Loans) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Summary Of Impaired Loans [Abstract]
Impaired loans with a specific allowance	$ 11,411,000	$ 12,217,000	$ 27,526,000
Impaired loans without a specific allowance	18,008,000	20,306,000	21,247,000
Total impaired loans	29,419,000	32,523,000	48,773,000
Allowance for loan and lease losses related to impaired loans	2,894,000	3,058,000	5,149,000
Allowance for loan and lease losses related to loans collectively evaluated	34,908,000	35,708,000	37,808,000
Total allowance for loan and lease losses	37,802,000	38,766,000	42,957,000
Average impaired loans for the period	34,331,000	38,379,000	57,438,000
Contractual interest income due on impaired loans during the period	2,339,000	2,612,000	4,433,000
Interest income on impaired loans recognized on a cash basis	773,000	1,374,000	1,121,000
Interest income on impaired loans recognized on an accrual basis	$ 280,000	$ 473,000	$ 560,000