Allowance for Loan Losses - Performing and Nonperforming Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Performing	$ 169,406	$ 153,472
Nonperforming	53	0
Total	169,459	153,472
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	154,464	140,481
Nonperforming	53	0
Total	154,517	140,481
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	5,594	4,448
Nonperforming		0
Total	5,594	4,448
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	9,348	8,543
Nonperforming		0
Total	$ 9,348	$ 8,543