Supplementary Balance Sheet Information - Accumulated Other Comprehensive Loss (AOCL) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	$ 2,585,906
Ending Balance	2,494,594	$ 2,585,906
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(65,275)
Reclassification from adoption of ASU 2016-01 (Note 1)		(5,052)
Pretax Amount	1,386
Tax Effect	311
Net-of-tax Amount	1,075
Ending Balance	(64,200)	(65,275)
Accumulated Other Comprehensive Income (Loss) | Previously reported
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(60,223)
Ending Balance		(60,223)
Foreign currency translation adjustments and transfers from noncontrolling interests
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(63,186)
Pretax Amount	420
Tax Effect	4
Net-of-tax Amount	416
Ending Balance	(62,770)	(63,186)
Foreign currency translation adjustments and transfers from noncontrolling interests | Previously reported
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(63,186)
Ending Balance		(63,186)
Gain on available-for-sale securities
Accumulated Other Comprehensive Loss (AOCL)
Reclassification from adoption of ASU 2016-01 (Note 1)		(5,052)
Gain on available-for-sale securities | Previously reported
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	5,052
Ending Balance		5,052
Change in postretirement healthcare plans
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(2,089)
Pretax Amount	966
Tax Effect	307
Net-of-tax Amount	659
Ending Balance	(1,430)	(2,089)
Change in postretirement healthcare plans | Previously reported
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	$ (2,089)
Ending Balance		$ (2,089)