Supplementary Balance Sheet Information - Accumulated Other Comprehensive Loss (AOCL) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Other comprehensive income (loss)
Beginning Balance	$ 2,240,993
Ending Balance	2,501,696
Reclassifications of AOCI	0
Accumulated Other Comprehensive Income (Loss)
Other comprehensive income (loss)
Beginning Balance	(36,148)
Pretax Amount	(9,164)
Tax Effect	(290)
Net-of-tax Amount	(8,874)
Ending Balance	(45,022)
Foreign currency translation adjustments and transfers from noncontrolling interests
Other comprehensive income (loss)
Beginning Balance	(43,464)
Pretax Amount	(9,651)
Tax Effect	(394)
Net-of-tax Amount	(9,257)
Ending Balance	(52,721)
Gain on available-for-sale securities
Other comprehensive income (loss)
Beginning Balance	8,446
Pretax Amount	950
Tax Effect	209
Net-of-tax Amount	741
Ending Balance	9,187
Change in postretirement healthcare plans
Other comprehensive income (loss)
Beginning Balance	(1,130)
Pretax Amount	(463)
Tax Effect	(105)
Net-of-tax Amount	(358)
Ending Balance	$ (1,488)