Allowance for Loan Losses - Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014 SecurityLoan	Sep. 30, 2013 SecurityLoan	Sep. 30, 2014 SecurityLoan	Sep. 30, 2013 SecurityLoan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	9	13	25	30
Pre-mod outstanding principal balance	$ 1,643	$ 1,225	$ 4,076	$ 6,902
Post-mod outstanding principal balance	1,551	1,229	3,969	6,915
Financial impact due to TDR taken as additional provision	104	61	180	485
Number that defaulted during the period		5	4	15
Recorded investment of TDRs that defaulted during the period		774	691	2,716
Financial impact due to the default of previous TDR taken as charge-offs or additional provisions		7	(8)	9
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	1	4	4	6
Pre-mod outstanding principal balance	48	607	854	1,039
Post-mod outstanding principal balance	50	607	857	1,043
Financial impact due to TDR taken as additional provision			37	151
Number that defaulted during the period			1	2
Recorded investment of TDRs that defaulted during the period			152	181
Financial impact due to the default of previous TDR taken as charge-offs or additional provisions				(3)
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	3	1	7	7
Pre-mod outstanding principal balance	1,156	25	1,980	4,580
Post-mod outstanding principal balance	1,059	26	1,890	4,581
Financial impact due to TDR taken as additional provision	4	4	22	26
Number that defaulted during the period		3	2	7
Recorded investment of TDRs that defaulted during the period		674	423	1,065
Home equity lines of credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	1	3	4	10
Pre-mod outstanding principal balance	198	480	677	1,062
Post-mod outstanding principal balance	200	482	691	1,069
Financial impact due to TDR taken as additional provision		27		220
Number that defaulted during the period		2		2
Recorded investment of TDRs that defaulted during the period		100		100
Financial impact due to the default of previous TDR taken as charge-offs or additional provisions		7		7
Home equity loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number			1
Pre-mod outstanding principal balance			32
Post-mod outstanding principal balance			33
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	1		1
Pre-mod outstanding principal balance	147		147
Post-mod outstanding principal balance	147		147
Financial impact due to TDR taken as additional provision	66		66
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	3	5	6	7
Pre-mod outstanding principal balance	94	113	166	221
Post-mod outstanding principal balance	95	114	167	222
Financial impact due to TDR taken as additional provision	34	30	55	88
Number that defaulted during the period			1	3
Recorded investment of TDRs that defaulted during the period			116	1,297
Financial impact due to the default of previous TDR taken as charge-offs or additional provisions			(8)
Construction [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number			1
Pre-mod outstanding principal balance			102
Post-mod outstanding principal balance			84
Number that defaulted during the period				1
Recorded investment of TDRs that defaulted during the period				73
Financial impact due to the default of previous TDR taken as charge-offs or additional provisions				5
Construction [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number			1
Pre-mod outstanding principal balance			118
Post-mod outstanding principal balance			$ 100