Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net loss	$ (18,521)	$ (4,655)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	34,011	34,761
Deferred income taxes	(7,791)	(3,572)
Loss (gain) on disposal of assets	7	(3,939)
Equity in loss of unconsolidated affiliate, net	1,994	76
Inventory valuation reserves	2,214	2,613
Changes in operating assets and liabilities	(19,863)	(24,485)
Net cash (used in) provided by operating activities	(7,949)	799
Investing activities:
Purchase of property and equipment	(43,892)	(39,908)
Proceeds from asset dispositions	17	10,998
Purchase of short-term investments	(134,518)	(151,436)
Proceeds from sale of short-term investments	187,217	148,838
Payment of deposits on aircraft	(110)	(131)
Net cash provided by (used in) investing activities	8,714	(31,639)
Financing activities:
Proceeds from line of credit	66,525	150,800
Payments on line of credit	(67,300)	(113,300)
Repurchase of common stock	(263)	(500)
Net cash (used in) provided by financing activities	(1,038)	37,000
(Decrease) increase in cash	(273)	6,160
Cash, beginning of period	2,596	2,407
Cash, end of period	2,323	8,567
Cash paid during the period for:
Interest	15,250	14,329
Income taxes	1,131	1,879
Noncash investing activities:
Other current liabilities and accrued payables related to purchase of property and equipment	$ 15	$ 64