Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 101		$ 315
Interest cost	$ 298	329	$ 893	986
Expected return on plan assets	(378)	(431)	(1,134)	(1,292)
Amortization of net actuarial loss	59	57	178	170
Net periodic benefit cost (gain)	(21)	56	(63)	179
Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	2	2
Amortization of loss	2	2	7	6
Net periodic benefit cost (gain)	$ 3	$ 3	$ 9	$ 8