Allowance for Loan Losses - Performing and Nonperforming Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Performing	$ 180,921	$ 173,309
Nonperforming	0	0
Total	180,921	173,309
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	163,051	158,169
Nonperforming	0	0
Total	163,051	158,169
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	8,466	5,808
Nonperforming	0	0
Total	8,466	5,808
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	9,404	9,332
Nonperforming	0	0
Total	$ 9,404	$ 9,332