Fair Value - Quantitative Information about Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Impaired Loans - Commercial Mortgages [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 3,148	$ 3,000
Impaired Loans - Commercial Mortgages [Member] | Minimum [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	11.00%	17.00%
Impaired Loans - Commercial Mortgages [Member] | Maximum [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	97.00%	61.00%
Impaired Loans - Commercial Mortgages [Member] | Weighted Average [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	(28.00%)	(22.00%)
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	3,058	3,274
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value		$ 432
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Minimum [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	8.00%
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Maximum [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	9.00%	9.00%
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Income approach		2.00%
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Weighted Average [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	(9.00%)