Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 357,543	$ 405,232
Interest expense	(4,128)	(3,388)
Interest and investment income	328	1,259
Income (loss) before income taxes	(5,664)	(27,090)
Provision for (benefit from) income taxes	(378)	1,791
Net income (loss)	(6,042)	(25,299)
Reclassification out of Accumulated Other Comprehensive Income | Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest expense	(624)	(216)
Provision for (benefit from) income taxes	0	0
Net income (loss)	(624)	(216)
Reclassification out of Accumulated Other Comprehensive Income | Pension, postretirement and other post-employment benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of actuarial gains (losses), net	(591)	234
Amortization of prior service credits	44	27
Pension settlement		(4)
Income (loss) before income taxes	(547)	257
Provision for (benefit from) income taxes	0	0
Net income (loss)	(547)	257
Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and investment income	10	(1)
Provision for (benefit from) income taxes	0	0
Net income (loss)	$ 10	$ (1)