Credit Quality Assessment (Summary of Impaired Loans) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Credit Quality Assessment [Abstract]
Impaired loans with a specific allowance	$ 9,654	$ 11,411
Impaired loans without a specific allowance	21,251	18,008
Total impaired loans	30,905	29,419
Allowance for loan and lease losses related to impaired loans	3,002	2,894
Allowance for loan and lease losses related to loans collectively evaluated	36,659	34,908
Total allowance for loan and lease losses	39,661	37,802
Average impaired loans for the period	30,055	34,331
Contractual interest income due on impaired loans during the period	2,016	2,339
Interest income on impaired loans recognized on a cash basis	745	773
Interest income on impaired loans recognized on an accrual basis	$ 239	$ 280