Supplementary Balance Sheet Information - Accumulated Other Comprehensive Loss (AOCL) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Other comprehensive income (loss)
Beginning Balance	$ 2,240,993
Ending Balance	2,394,574
Reclassifications of AOCI	0
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss)
Beginning Balance	(36,148)
Pretax Amount	16,469
Tax Effect	1,540
Net-of-tax Amount	14,929
Ending Balance	(21,219)
Foreign currency translation adjustments and transfers from noncontrolling interests
Other comprehensive income (loss)
Beginning Balance	(43,464)
Pretax Amount	13,390
Tax Effect	895
Net-of-tax Amount	12,495
Ending Balance	(30,969)
Gain on available-for-sale securities
Other comprehensive income (loss)
Beginning Balance	8,446
Pretax Amount	3,310
Tax Effect	729
Net-of-tax Amount	2,581
Ending Balance	11,027
Change in postretirement healthcare plans
Other comprehensive income (loss)
Beginning Balance	(1,130)
Pretax Amount	(231)
Tax Effect	(84)
Net-of-tax Amount	(147)
Ending Balance	$ (1,277)