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	Mar. 31, 2014	Dec. 31, 2013
Impaired Loans - Commercial Mortgages [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 2,994	$ 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	15.00%	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	60.00%	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	(26.00%)	(22.00%)
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Sales Comparison Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	3,004	3,274
Impaired Loans - Commercial, Industrial, and Agricultural [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 200	$ 432
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	20.00%	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	54.00%	2.00%