Pension Plans and Other Postretirement Benefits - Domestic and Foreign Pension and Postretirement Defined Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Total net pension and postretirement benefits (credit) cost	$ (903)	$ 19	$ (1,793)	$ (7)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,259	1,020	2,527	2,023
Interest cost	8,016	8,320	16,043	16,608
Expected return on assets	(10,760)	(9,931)	(21,524)	(19,839)
Amortization of prior service benefit	24	46	46	73
Total net pension and postretirement benefits (credit) cost	(1,461)	(545)	(2,908)	(1,135)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	30	30	59	61
Interest cost	542	585	1,084	1,170
Expected return on assets	(2)	(27)	(4)	(55)
Amortization of prior service benefit	(12)	(24)	(24)	(48)
Total net pension and postretirement benefits (credit) cost	$ 558	$ 564	$ 1,115	$ 1,128