Fair Value - Quantitative Information about Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Non Recurring Basis (Detail) - Impaired Loans - Commercial Mortgages [Member] - Sales Comparison Valuation Technique [Member] - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 2,247	$ 2,247
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	24.00%	25.00%
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	68.00%	69.00%
Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Sales comparison approach	(34.00%)	(36.00%)