Allowance for Loan Losses - Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 SecurityLoan	Mar. 31, 2014 SecurityLoan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	5	9
Pre-mod outstanding principal balance	$ 608	$ 1,488
Post-mod outstanding principal balance	611	1,456
Financial impact due to TDR taken as additional provision	172	64
Number that defaulted during the period	1	2
Recorded investment of TDRs that defaulted during the period	47	376
Financial impact due to the default of previous TDR taken as charge-offs or additional provisions		(8)
Home equity lines of credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number		2
Pre-mod outstanding principal balance		279
Post-mod outstanding principal balance		279
Number that defaulted during the period	1
Recorded investment of TDRs that defaulted during the period	47
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	1	2
Pre-mod outstanding principal balance	108	695
Post-mod outstanding principal balance	110	695
Financial impact due to TDR taken as additional provision	8	37
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	1	2
Pre-mod outstanding principal balance	124	256
Post-mod outstanding principal balance	124	259
Financial impact due to TDR taken as additional provision	(5)	9
Number that defaulted during the period		1
Recorded investment of TDRs that defaulted during the period		260
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	2
Pre-mod outstanding principal balance	89
Post-mod outstanding principal balance	89
Financial impact due to TDR taken as additional provision	5
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number	1	1
Pre-mod outstanding principal balance	287	38
Post-mod outstanding principal balance	288	38
Financial impact due to TDR taken as additional provision	164	18
Number that defaulted during the period		1
Recorded investment of TDRs that defaulted during the period		116
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		85
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