Employee Benefit Plans - Unfunded Post Retirement Benefits Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 2,427	$ 2,740	$ 3,409
Interest cost	89	83	114
Service cost	74	87	103
Actual claims	(42)	(79)	(78)
Actuarial (gain) loss	(518)	(404)	(808)
Benefit obligation at end of year	$ 2,030	$ 2,427	$ 2,740