CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
OPERATING ACTIVITIES
Net loss	$ (10,388)	$ (185,516)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation, amortization and other non-cash charges	35,589	58,924
Stock-based compensation expense	3,010	4,114
Gain on disposition of assets, net	(4,571)	(4,013)
Deferred income tax benefit	(4,338)	(36,723)
Impairment and other non-cash charges		206,264
(Increase) decrease in assets:
Accounts receivable	(18,779)	133,223
Income taxes receivable	31,941	(22,762)
Inventories	1,836	7,320
Prepaid expenses	3,465	4,601
Other current assets	508	235
Other non-current assets	1,191	(423)
Increase (decrease) in liabilities:
Accounts payable	12,168	(27,451)
Income taxes payable	303	(1,099)
Accrued payroll and related expenses	2,635	(6,373)
Accrued insurance expenses	(482)	(1,228)
Accrued state, local and other taxes	1,091	1,304
Other accrued expenses	49	(4,966)
Pension liabilities	113	(610)
Long-term accrued insurance expenses	(1,341)	(1,045)
Other long-term liabilities	866	(1,677)
Net cash provided by operating activities	54,866	122,099
INVESTING ACTIVITIES
Capital expenditures	(25,875)	(38,659)
Proceeds from sale of assets	8,094	12,740
Net cash used for investing activities	(17,781)	(25,919)
FINANCING ACTIVITIES
Cash paid for common stock purchased and retired	(566)	(798)
Net cash used for financing activities	(566)	(798)
Net increase in cash and cash equivalents	36,519	95,382
Cash and cash equivalents at beginning of period	84,496	50,023
Cash and cash equivalents at end of period	121,015	145,405
Supplemental cash flows disclosure:
Income taxes refund, net	(28,386)	(9,847)
Supplemental disclosure of noncash investing activities:
Capital expenditures included in accounts payable	$ 4,131	$ 2,185