Fair Value - Assets and Liabilities Measured at Fair Value on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commercial Mortgages [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	$ 3,148	$ 3,000
Commercial, Industrial, and Agricultural [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	3,058	3,706
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial Mortgages [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial, Industrial, and Agricultural [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgages [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) [Member] | Commercial, Industrial, and Agricultural [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	0	0
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgages [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	3,148	3,000
Significant Unobservable Inputs (Level 3) [Member] | Commercial, Industrial, and Agricultural [Member]
Impaired loans:
Fair value assets and liabilities measured on a nonrecurring basis	$ 3,058	$ 3,706