Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) - Treasury Options - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets-other	$ 144	$ 1,900
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets-other	$ 144	$ 1,900