Employee Benefit Plans - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Conditional age-1 for availing plan	55 years
Conditional age-2 for availing plan	65 years
Conditional years of service -1 for availing plan	10 years
Conditional years of service-2 for availing plan	5 years
Gain on curtailment of post-retirement benefit plan	$ 352
Other Postretirement Benefit Plan, Defined Benefit
Defined Contribution Plan Disclosure [Line Items]
Gain on curtailment of post-retirement benefit plan	$ 352