Supplementary Balance Sheet Information - Accumulated Other Comprehensive Loss (AOCL) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	$ 2,585,906
Ending Balance	2,352,760	$ 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	11,187
Tax Effect	940
Net-of-tax Amount	10,247
Ending Balance	(55,028)	(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	11,418
Tax Effect	992
Net-of-tax Amount	10,426
Ending Balance	(52,760)	(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	(231)
Tax Effect	(52)
Net-of-tax Amount	(179)
Ending Balance	(2,268)	(2,089)
Change in postretirement healthcare plans | Previously reported
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	$ (2,089)
Ending Balance		$ (2,089)