CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING ACTIVITIES
Net income	$ 52,130	$ 3,634
Adjustments to reconcile net income to net cash provided by (used for) operating activities:
Depreciation, amortization and other non-cash charges	38,148	45,412
Stock-based compensation expense	2,555	2,687
Gain on disposition of assets, net	(1,363)	(1,517)
Deferred income tax benefit	(1,034)	(11,667)
(Increase) decrease in assets:
Accounts receivable	(6,953)	(77,406)
Income taxes receivable	10,300	8,713
Inventories	(6,215)	(3,595)
Prepaid expenses	2,039	(179)
Other current assets	(1,535)	(429)
Other non-current assets	295	(749)
Increase (decrease) in liabilities:
Accounts payable	11,990	19,775
Income taxes payable	4,786	(1,124)
Accrued payroll and related expenses	3,169	5,399
Accrued insurance expenses	374	582
Accrued state, local and other taxes	970	1,652
Other accrued expenses	169	(4,938)
Pension liabilities	(588)	986
Long-term accrued insurance expenses	935	345
Other long-term liabilities	(509)	(30)
Net cash provided by (used for) operating activities	109,663	(12,449)
INVESTING ACTIVITIES
Capital expenditures	(50,482)	(11,707)
Proceeds from sale of assets	3,119	2,493
Net cash used for investing activities	(47,363)	(9,214)
FINANCING ACTIVITIES
Payment of dividends	(21,657)
Cash paid for common stock purchased and retired	(30,710)	(5,674)
Net cash used for financing activities	(52,367)	(5,674)
Net increase (decrease) in cash and cash equivalents	9,933	(27,337)
Cash and cash equivalents at beginning of period	91,050	131,835
Cash and cash equivalents at end of period	100,983	104,498
Supplemental cash flows disclosure:
Interest paid, net of amounts capitalized	62
Income taxes paid, net	292	2,199
Supplemental disclosure of noncash investing activities:
Capital expenditures included in accounts payable	$ 18,823	$ 5,322