Stock-based Compensation Plans - Summary of Change in Benefit Obligations Recognized in Comprehensive Income on Pre-tax Basis and Amounts Recognized in Consolidated Balance Sheets (Detail) - Other Post Retirement Benefits $ in Thousands	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 1,769
Change in benefit obligations (recognized in comprehensive income – pretax)
Prior service cost	1,769
Total other comprehensive income (loss) at December 31, 2017	1,769
Amounts recognized in the consolidated balance sheets:
Noncurrent liability-accrued benefit cost	$ 1,769