Accumulated Other Comprehensive (Loss) Income - Summary of Amounts Reclassified (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee benefit costs:
Loss from continuing operations before income taxes	$ (243,634)	$ (272,905)
Income tax benefit	2,164	53,287
Net loss	(446,899)	(316,319)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of actuarial loss
Employee benefit costs:
Miscellaneous income	3,929	959
Reclassification out of Accumulated Other Comprehensive Income | Settlement
Employee benefit costs:
Miscellaneous income	3,349	6,446
Reclassification out of Accumulated Other Comprehensive Income | Employee benefit costs
Employee benefit costs:
Loss from continuing operations before income taxes	7,278	7,405
Income tax benefit	0	0
Net loss	$ 7,278	$ 7,405