Assets Measured at Fair Value on Recurring Basis for Pension Plan (Detail) - Pension Plans - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 91,058	$ 87,194	$ 86,744
Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	82,230	77,843
Mutual Fund | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	42,134	40,124
Mutual Fund | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	33,924	32,192
Mutual Fund | Equity And Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	6,172	5,527
Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	8,828	9,351
Fair Value, Inputs, Level 1 | Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	82,230	77,843
Fair Value, Inputs, Level 1 | Mutual Fund | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	42,134	40,124
Fair Value, Inputs, Level 1 | Mutual Fund | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	33,924	32,192
Fair Value, Inputs, Level 1 | Mutual Fund | Equity And Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 6,172	$ 5,527