Pensions and Postretirement Benefits Other than Pensions - Components of Net Periodic Benefit Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	$ 487	$ 501	$ 974	$ 1,002
Interest cost	2,313	2,516	4,625	5,031
Amortization of prior service credit	(135)	(142)	(270)	(283)
Net periodic benefit cost	2,665	2,875	5,329	5,750
Domestic | Pension Benefits
Components of net periodic benefit cost:
Service cost	2,580	2,465	5,160	4,930
Interest cost	9,210	9,813	18,419	19,626
Expected return on plan assets	(13,498)	(13,514)	(26,997)	(27,029)
Amortization of actuarial loss	8,235	9,280	16,471	18,561
Net periodic benefit cost	6,527	8,044	13,053	16,088
International | Pension Benefits
Components of net periodic benefit cost:
Service cost	0	0	0	0
Interest cost	2,840	2,860	5,746	5,630
Expected return on plan assets	(3,073)	(2,795)	(6,216)	(5,502)
Amortization of actuarial loss	1,085	1,351	2,195	2,661
Net periodic benefit cost	$ 852	$ 1,416	$ 1,725	$ 2,789