Loans and Leases - Reserve for Loan and Lease Losses Roll Forward (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
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				$ 24,494,000				$ 24,746,000	$ 24,494,000	$ 24,746,000	$ 29,870,000
Charge-offs									(8,850,000)	(13,619,000)	(16,735,000)
Recoveries									1,411,000	2,139,000	1,576,000
Provision (recovery of provision)	648,000	233,000	1,251,000	1,475,000	1,614,000	4,094,000	3,446,000	2,074,000	3,607,000	11,228,000	10,035,000
Ending balance	20,662,000				24,494,000				20,662,000	24,494,000	24,746,000
Amount of Loans Charged Off Prior to Being Transferred to Loans Held for Sale											1,300,000
Commercial, Financial and Agricultural [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				9,789,000				11,594,000	9,789,000	11,594,000	11,262,000
Charge-offs									(2,834,000)	(3,213,000)	(9,974,000)
Recoveries									247,000	320,000	484,000
Provision (recovery of provision)									(282,000)	1,088,000	9,822,000
Ending balance	6,920,000				9,789,000				6,920,000	9,789,000	11,594,000
Real Estate-Commercial and Construction [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				8,780,000				7,507,000	8,780,000	7,507,000	13,317,000
Charge-offs									(4,363,000)	(8,667,000)	(4,803,000)
Recoveries									524,000	1,104,000	334,000
Provision (recovery of provision)									4,002,000	8,836,000	(1,341,000)
Ending balance	8,943,000				8,780,000				8,943,000	8,780,000	7,507,000
Real Estate-Residential Secured for Business Purpose [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1,062,000				639,000	1,062,000	639,000	823,000
Charge-offs									(140,000)	(112,000)	0
Recoveries									60,000	13,000	60,000
Provision (recovery of provision)									(219,000)	522,000	(244,000)
Ending balance	763,000				1,062,000				763,000	1,062,000	639,000
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1,284,000				980,000	1,284,000	980,000	735,000
Charge-offs									(141,000)	(195,000)	(156,000)
Recoveries									34,000	13,000	7,000
Provision (recovery of provision)									(53,000)	486,000	394,000
Ending balance	1,124,000				1,284,000				1,124,000	1,284,000	980,000
Loans to Individuals [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				694,000				679,000	694,000	679,000	730,000
Charge-offs									(796,000)	(641,000)	(578,000)
Recoveries									265,000	174,000	130,000
Provision (recovery of provision)									197,000	482,000	397,000
Ending balance	360,000				694,000				360,000	694,000	679,000
Lease Financings [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1,285,000				1,326,000	1,285,000	1,326,000	1,344,000
Charge-offs									(576,000)	(791,000)	(1,224,000)
Recoveries									281,000	515,000	561,000
Provision (recovery of provision)									(5,000)	235,000	645,000
Ending balance	985,000				1,285,000				985,000	1,285,000	1,326,000
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1,600,000				2,021,000	1,600,000	2,021,000	1,659,000
Provision (recovery of provision)									(33,000)	(421,000)	362,000
Ending balance	$ 1,567,000				$ 1,600,000				$ 1,567,000	$ 1,600,000	$ 2,021,000