Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 97	$ 113
Interest cost	298	329
Expected return on plan assets	(476)	(431)
Amortization of net actuarial loss	59	57
Net periodic benefit cost (gain)	(22)	68
Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1
Amortization of loss	2	2
Net periodic benefit cost (gain)	$ 3	$ 3