Employee Benefit Plans - Unfunded Post Retirement Benefits Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 2,740	$ 3,409	$ 3,066
Interest cost	83	114	108
Service cost	87	103	103
Actual claims	(79)	(78)	(151)
Actuarial (gain) loss	(404)	(808)	283
Benefit obligation at end of year	$ 2,427	$ 2,740	$ 3,409