Stock-based Compensation Plans - Summary of Change in Post Retirement Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Changes in Benefit Obligations in Other Comprehensive Income (Loss):
Net (gain) loss	$ (39)	$ 532	$ (526)
Amortization of prior service cost	(369)	(369)	(369)
Other Post Retirement Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	1,957	1,355
Service cost	80	88
Interest cost	50	68
Actuarial (gain) loss	(39)	532
Benefits paid	(95)	(86)
Benefit obligation at end of year	1,953	1,957	$ 1,355
Amounts recognized in the consolidated balance sheet:
Long-term liabilities	1,953	1,957
Components of Net Periodic Post Retirement Benefit Cost:
Service cost	80	88
Interest cost	50	68
Amortization of prior service cost	369	369
Net periodic post retirement costs (recognized in general and administrative expense)	499	525
Other Changes in Benefit Obligations in Other Comprehensive Income (Loss):
Net (gain) loss	(39)	532
Prior service cost	0	0
Amortization of prior service cost	(369)	(369)
Total recognized in other comprehensive (loss) income	(408)	163
Total recognized in net periodic benefit cost and other comprehensive income	$ 91	$ 688