Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net income (loss)	$ 30,716	$ (121,343)
Adjustments to reconcile net income (loss) to net cash (used in) provided by operating activities:
Non-cash operating items (Note 2)	(34,767)	118,945
Changes in operating assets and liabilities:
Other current assets	(569)	(278)
Accrued employment costs and other current liabilities	(1,442)	(1,498)
Income taxes receivable and payable	34	(903)
Pension and other postretirement liabilities	(388)	(386)
Other liabilities	245	1,594
Net cash (used in) provided by operating activities	(6,171)	(3,869)
Cash, cash equivalents and restricted cash - period (decrease) increase	(6,171)	(3,869)
Cash, cash equivalents and restricted cash - beginning of year	31,935	259,371
Cash, cash equivalents and restricted cash - end of period	$ 25,764	$ 255,502