Pension Plans and Other Postretirement Benefits Components of Pension and Postretirement Benefits Expense (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss	$ (11,400)	$ 26,700
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 121	$ 115	$ 137
Interest cost			2,340	2,483	2,573
Expected return on assets			(110)	(187)	(263)
Actuarial (gain) loss			2,014	1,275	(5,707)
Amortization of prior service benefit			(95)	(95)	(95)
Total net pension benefits cost (credit)			$ 4,270	$ 3,591	$ (3,355)
Weighted-average assumption percentages:
Discount rate			4.35%	4.59%	4.15%
Expected return on plan assets			7.00%	7.00%	7.00%
Rate of compensation increase			3.50%	3.50%	3.50%
Net pension or postretirement benefits credit					$ 2,600
Pension Plans
Weighted-average assumption percentages:
Net pension or postretirement benefits credit				$ 10,800	6,200
U.S. Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 985	1,028	1,233
Interest cost			28,614	30,514	30,235
Expected return on assets			(36,243)	(36,445)	(40,495)
Actuarial (gain) loss			(13,910)	5,988	2,665
Amortization of prior service benefit			75	75	75
Total net pension benefits cost (credit)			$ (20,479)	$ 1,160	$ (6,287)
Weighted-average assumption percentages:
Discount rate			4.43%	4.67%	4.19%
Expected return on plan assets			6.89%	6.89%	6.88%
Rate of compensation increase			0.00%	0.00%	0.00%
Foreign Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 2,547	$ 3,133	$ 3,909
Interest cost			5,128	6,570	6,405
Expected return on assets			(4,441)	(4,027)	(3,670)
Actuarial (gain) loss			483	19,418	(27,043)
Amortization of prior service benefit			56	859	43
Total net pension benefits cost (credit)			$ 3,773	$ 25,953	$ (20,356)
Weighted-average assumption percentages:
Discount rate			2.00%	2.76%	2.22%
Expected return on plan assets			6.16%	6.66%	5.76%
Rate of compensation increase			3.18%	3.16%	3.15%