Stock-based Compensation Plans - Summary of Change in Post Retirement Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Other Changes in Benefit Obligations in Other Comprehensive Income (Loss)
Net gain	$ (526)
Prior service cost		$ 1,769
Amortization of prior service cost	(369)
Other Post Retirement Benefits
Change in Benefit Obligation
Benefit obligation at beginning of year	1,769
Prior service cost		1,769
Service cost	94
Interest cost	58
Actuarial gain	(526)
Benefits paid	(40)
Benefit obligation at end of year	1,355	1,769
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	1,355	1,769
Components of Net Periodic Post Retirement Benefit Cost
Service cost	94
Interest cost	58
Amortization of prior service cost	369
Net periodic post retirement costs (recognized in general and administrative expense)	521
Other Changes in Benefit Obligations in Other Comprehensive Income (Loss)
Net gain	(526)
Prior service cost		1,769
Amortization of prior service cost	(369)
Total recognized in other comprehensive (loss) income	(895)	1,769
Total recognized in net periodic benefit cost and other comprehensive (loss) income	$ (374)	$ 1,769