Pensions and Postretirement Benefits Other than Pensions - Components of Net Periodic Benefit Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost					$ 11,771	$ 13,559
Pension settlement charge	$ 0	$ 11,462	$ 0	$ 11,462
Net periodic benefit cost					$ 64,842	$ 58,384
Pension Benefits - Domestic
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	2,465	2,403	7,395	7,210
Interest cost	9,813	10,617	29,439	31,850
Expected return on plan assets	(13,515)	(13,391)	(40,544)	(40,175)
Amortization of actuarial loss	9,281	9,576	27,842	28,729
Pension settlement charge	0	11,462	0	11,462
Net periodic benefit cost	8,044	20,667	24,132	39,076
Pension Benefits - International
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	2	0	7
Interest cost	2,927	3,417	8,557	10,877
Expected return on plan assets	(2,860)	(2,744)	(8,362)	(8,736)
Amortization of actuarial loss	1,384	1,244	4,045	3,961
Net periodic benefit cost	1,451	1,919	4,240	6,109
Other Postretirement Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	501	537	1,502	1,611
Interest cost	2,515	2,705	7,547	8,115
Amortization of prior service credit	(141)	(141)	(424)	(424)
Net periodic benefit cost	$ 2,875	$ 3,101	$ 8,625	$ 9,302