Employee Benefit Plans - Net Period Benefit Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Service cost	$ 1,735	$ 1,933	$ 1,601
Interest cost	714	645	599
Expected return on plan assets	(514)	(401)	(416)
Amortization of actuarial (gain)/loss	(153)	256	90
Net periodic benefit cost	$ 1,782	$ 2,433	$ 1,874