Pension and Postretirement Benefits (Net Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postretirement Medical Benefits
Components of the net periodic cost for retirement and postretirement benefits
Interest cost	$ 754	$ 779	$ 919
Amortization of unrecognized net loss	(215)	(764)	(275)
Amortization of unrecognized prior service cost (benefit)	122	122	122
U.S. net pension expense	661	137	766
United States | Pension Plan
Components of the net periodic cost for retirement and postretirement benefits
Service cost	23,245	22,195	22,257
Interest cost	17,584	15,789	16,878
Expected return on plan assets	(25,645)	(25,704)	(24,505)
Settlement loss (gain) and other	0	(462)	(216)
Amortization of unrecognized prior service cost	164	164	112
Amortization of unrecognized net loss	3,675	5,514	6,021
Amortization of unrecognized prior service cost (benefit)	211	0
U.S. net pension expense	19,023	17,496	20,547
Foreign Plan | Pension Plan
Components of the net periodic cost for retirement and postretirement benefits
Service cost	5,728	7,208	7,247
Interest cost	8,867	8,970	9,320
Expected return on plan assets	(7,535)	(8,747)	(8,834)
Settlement loss (gain) and other	859	(521)	2,434
Amortization of unrecognized net loss	2,933	3,626	3,741
Amortization of unrecognized prior service cost (benefit)	265	33	(4)
U.S. net pension expense	$ 11,117	$ 10,569	$ 13,904