Pension and Employee Benefit Plans - Schedule of Changes in Projected Benefit Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in projected benefit obligation:
Interest cost	$ 1,034	$ 1,303	$ 1,190
Change in plan assets:
Fair value of plan assets at beginning of year	27,099
Fair value of plan assets at end of year	28,545	27,099
Funded status at end of year	$ 9,700	$ 8,800	$ 8,800
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	2.95%	4.05%	3.35%
Pension Benefits [Member]
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 35,985	$ 32,998	$ 36,327
Interest cost	1,034	1,303	1,190
Actuarial loss (gain)	3,323	3,704	(2,629)
Benefits paid	(2,070)	(2,020)	(1,890)
Projected benefit obligation at end of year	38,272	35,985	32,998
Change in plan assets:
Fair value of plan assets at beginning of year	27,099	24,197	26,836
Actual return (loss) on plan assets	1,629	4,431	(1,388)
Employer contribution	1,887	491	639
Benefits paid	(2,070)	(2,020)	(1,890)
Fair value of plan assets at end of year	28,545	27,099	24,197
Funded status at end of year	$ (9,727)	$ (8,886)	$ (8,801)
Weighted-average assumptions used to determine benefit obligations for the year ended December 31:
Discount rate	2.10%	2.95%	4.05%