Pension Plans and Other Postretirement Benefits - Domestic and Foreign Pension and Postretirement Defined Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Total net pension and postretirement benefits (credit) cost	$ (915)	$ 74	$ (2,708)	$ 67
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,238	1,067	3,765	3,090
Interest cost	7,967	8,375	24,010	24,983
Expected return on assets	(10,703)	(9,960)	(32,227)	(29,799)
Amortization of prior service benefit	25	29	71	102
Total net pension and postretirement benefits (credit) cost	(1,473)	(489)	(4,381)	(1,624)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	29	30	88	91
Interest cost	542	585	1,626	1,755
Expected return on assets	(1)	(28)	(5)	(83)
Amortization of prior service benefit	(12)	(24)	(36)	(72)
Total net pension and postretirement benefits (credit) cost	$ 558	$ 563	$ 1,673	$ 1,691