Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 405,232	$ 555,183
Interest expense	(3,388)	(4,432)
Provision for (benefit from) income taxes	1,791	(70)
Interest and investment income	1,259	2,143
Net income (loss)	(25,299)	72,741
Reclassification out of Accumulated Other Comprehensive Income | Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues		361
Interest expense	(216)	515
Provision for (benefit from) income taxes	0	0
Net income (loss)	(216)	876
Reclassification out of Accumulated Other Comprehensive Income | Pension, postretirement and other post-employment benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Provision for (benefit from) income taxes	0	0
Amortization of actuarial gains (losses), net	234	0
Amortization of prior service credits	27
Pension settlement	(4)
Net income (loss)	257
Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Provision for (benefit from) income taxes	0	$ 0
Interest and investment income	(1)
Net income (loss)	$ (1)