CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES
Net income (loss)	$ 162,511	$ (141,246)	$ (99,561)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, amortization and other non-cash charges	166,558	221,038	275,413
Stock-based compensation expense	11,090	10,218	9,960
(Gain) loss on disposition of assets, net	(4,530)	(7,920)	6,417
Deferred income tax benefit	(42,609)	(34,209)	(33,013)
Excess tax benefits for share-based payments		(427)	(1,410)
(Increase) decrease in assets:
Accounts receivable	(208,642)	64,715	401,753
Income taxes receivable	16,931	(5,355)	(20,867)
Inventories	(6,275)	20,294	26,667
Prepaid expenses	(2,272)	2,244	161
Other current assets	(1,222)	2	(2,881)
Other non-current assets	(4,779)	(1,851)	1,768
Increase (decrease) in liabilities:
Accounts payable	29,176	(6,250)	(62,446)
Income taxes payable	(1,705)	(2,710)	6,695
Accrued payroll and related expenses	11,408	(4,540)	(33,143)
Accrued insurance expenses	1,200	(197)	(1,336)
Accrued state, local and other taxes	5,561	256	(3,983)
Other accrued expenses	(5,335)	5,017	(180)
Pension liabilities	4,398	(1,385)	1,021
Long-term accrued insurance expenses	839	(1,811)	1,249
Other long-term liabilities	1,401	(14,179)	1,508
Net cash provided by operating activities	133,704	101,704	473,792
INVESTING ACTIVITIES
Capital expenditures	(117,509)	(33,938)	(167,426)
Proceeds from sale of assets	13,123	12,599	9,843
Net cash used for investing activities	(104,386)	(21,339)	(157,583)
FINANCING ACTIVITIES
Payment of dividends	(43,319)	(10,861)	(33,602)
Borrowings from notes payable to banks			613,300
Repayments of notes payable to banks			(837,800)
Debt issue costs for notes payable to banks		(35)
Excess tax benefits for share-based payments		427	1,410
Cash paid for common stock purchased and retired	(26,784)	(3,257)	(4,093)
Net cash used for financing activities	(70,103)	(13,726)	(260,785)
Net (decrease) increase in cash and cash equivalents	(40,785)	66,639	55,424
Cash and cash equivalents at beginning of year	131,835	65,196	9,772
Cash and cash equivalents at end of year	$ 91,050	$ 131,835	$ 65,196