Employee Benefit Plans - Components of Net Periodic Pension Cost for Defined Benefit Pension Plan and Retirement Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Service cost	$ 601	$ 531	$ 531
Interest cost	1,268	1,329	1,367
Expected return on plan assets	(1,784)	(1,530)	(1,482)
Amortization of actuarial losses	743	810	762
Net periodic pension cost	$ 828	$ 1,140	$ 1,178