Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (24,075)	$ (18,521)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	38,598	34,011
Deferred income taxes	(7,446)	(7,791)
Loss (gain) on asset dispositions	708	7
Equity in loss of unconsolidated affiliate, net	(45)	1,994
Inventory valuation reserves	3,308	2,214
Changes in operating assets and liabilities	(5,638)	(19,863)
Net cash provided by (used in) operating activities	5,410	(7,949)
Investing activities:
Purchase of property and equipment	(18,098)	(43,892)
Proceeds from asset dispositions	1,453	17
Purchase of short-term investments	(260,996)	(134,518)
Proceeds from sale of short-term investments	264,918	187,217
Payment of deposits on aircraft	0	(110)
Loan to unconsolidated affiliate	(274)	0
Net cash (used in) provided by investing activities	(12,997)	8,714
Financing activities:
Proceeds from line of credit	34,295	66,525
Payments on line of credit	(29,575)	(67,300)
Repurchase of common stock	(51)	(263)
Net cash provided by (used in) financing activities	4,669	(1,038)
Decrease in cash	(2,918)	(273)
Cash, beginning of period	8,770	2,596
Cash, end of period	5,852	2,323
Cash paid during the period for:
Interest	15,755	15,250
Income taxes	813	1,131
Noncash investing activities:
Other current liabilities and accrued payables related to purchase of property and equipment	$ 272	$ 15