Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities:
Net (loss) earnings	$ (4,655)	$ 16,817
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	34,761	36,511
Deferred income taxes	(3,572)	10,063
Gain on asset dispositions	(3,939)	(73)
Equity in loss of unconsolidated affiliate	76	174
Inventory valuation reserves	2,613	(254)
Changes in operating assets and liabilities	(24,485)	6,070
Net cash provided by operating activities	799	69,308
Investing activities:
Purchase of property and equipment	(39,908)	(29,502)
Proceeds from asset dispositions	10,998	567
Purchase of short-term investments	(151,436)	(290,469)
Proceeds from sale of short-term investments	148,838	257,454
Payments of deposits on aircraft	(131)	(131)
Net cash used in investing activities	(31,639)	(62,081)
Financing activities:
Proceeds from line of credit	150,800	119,740
Payments on line of credit	(113,300)	(127,240)
Repurchase of common stock	(500)	(2,338)
Net cash provided by (used in) financing activities	37,000	(9,838)
Increase (decrease) in cash	6,160	(2,611)
Cash, beginning of period	2,407	6,270
Cash, end of period	8,567	3,659
Cash paid during the period for:
Interest	14,329	13,696
Income taxes	1,879	3,061
Noncash investing activities:
Other current liabilities and accrued payables related to purchase of property and equipment	$ 64	$ 27,757