Credit Quality Assessment (Impaired Loans by Portfolio) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable Impaired [Line Items]
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
Commercial
Financing Receivable Impaired [Line Items]
Average impaired loans for the period	5,308,000	7,153,000
Contractual interest income due on impaired loans during the period	311,000	452,000
Interest income on impaired loans recognized on a cash basis	252,000	238,000
Interest income on impaired loans recognized on an accrual basis	63,000	133,000
All Other
Financing Receivable Impaired [Line Items]
Average impaired loans for the period	7,082,000	6,784,000
Contractual interest income due on impaired loans during the period	87,000	227,000
Interest income on impaired loans recognized on a cash basis	60,000	83,000
Interest income on impaired loans recognized on an accrual basis	106,000	233,000
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable Impaired [Line Items]
Average impaired loans for the period	3,651,000	5,451,000
Contractual interest income due on impaired loans during the period	352,000	654,000
Interest income on impaired loans recognized on a cash basis	39,000	253,000
Interest income on impaired loans recognized on an accrual basis	0	0
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable Impaired [Line Items]
Average impaired loans for the period	9,327,000	10,605,000
Contractual interest income due on impaired loans during the period	730,000	587,000
Interest income on impaired loans recognized on a cash basis	78,000	75,000
Interest income on impaired loans recognized on an accrual basis	111,000	30,000
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable Impaired [Line Items]
Average impaired loans for the period	8,963,000	8,386,000
Contractual interest income due on impaired loans during the period	859,000	692,000
Interest income on impaired loans recognized on a cash basis	344,000	725,000
Interest income on impaired loans recognized on an accrual basis	$ 0	$ 77,000