Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Purchase of common stock	$ (3,581)	$ (11,184)	$ (63,570)
Withholding taxes paid for conversion of employee stock awards	2,325	2,914	2,300
OPERATING ACTIVITIES:
Net earnings (loss) from continuing operations	67,883	21,740	21,060
Net earnings (loss) from discontinued operations	1,402	(3,245)	2,428
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	204,559	170,751	140,002
Pension and post-retirement	3,766	20,933	11,532
Deferred income taxes	18,986	(30,771)	13,807
Amortization of stock-based compensation	5,047	3,632	3,165
Net (gain) loss on financial instruments	8	(1,370)	(969)
Changes in assets and liabilities:
Accounts receivable	25,380	(31,313)	(9,597)
Inventory and prepaid supplies	(3,273)	(4,107)	(5,269)
Accounts payable	10,724	23,500	5,603
Unearned revenue	(3,824)	(7,331)	(3,216)
Accrued expenses, salaries, wages, benefits and other liabilities	3,605	780	5,678
Pension and post-retirement assets	(35,293)	(13,083)	(11,819)
Other	6,359	3,717	1,611
NET CASH PROVIDED BY OPERATING ACTIVITIES	298,025	234,992	193,092
INVESTING ACTIVITIES:
Expenditures for property and equipment	(292,915)	(296,939)	(264,477)
Proceeds from property and equipment	17,570	381	12,380
Investment in nonconsolidated affiliate	(866,558)	(11,792)	17,395
Redemption of long term deposits	0	9,975	0
NET CASH (USED IN) INVESTING ACTIVITIES	(1,141,903)	(298,375)	(269,492)
FINANCING ACTIVITIES:
Principal payments on long term obligations	(58,640)	(254,446)	(44,069)
Proceeds from borrowings	945,000	115,000	185,000
Proceeds from convertible notes	0	258,750	0
Payments for financing costs	(9,953)	7,887	0
Purchase convertible note hedges	0	(56,097)	0
NET CASH PROVIDED BY FINANCING ACTIVITIES	870,501	79,724	75,061
Proceeds from issuance of warrants	0	38,502	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	26,623	16,341	(1,339)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	32,699	16,358	17,697
CASH AND CASH EQUIVALENTS AT END OF PERIOD	59,322	32,699	16,358
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid, net of amount capitalized	17,278	13,693	10,738
Federal alternative minimum and state income taxes paid	1,213	1,938	923
SUPPLEMENTAL NON-CASH INFORMATION:
Accrued expenditures for property and equipment	11,234	25,142	9,118
Net (gain) loss on financial instruments	7,296	(79,789)	(18,107)
Accrued consideration for acquisition	$ 7,845	$ 0	$ 0