Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating activities:
Net earnings	$ 8,838	$ 2,178
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	10,101	8,402
Deferred income taxes	5,892	1,482
Loss (gain) on asset dispositions	25	(11)
Equity in loss of unconsolidated affiliate	487
Other	(53)	207
Changes in operating assets and liabilities	4,813	5,788
Net cash provided by operating activities	30,103	18,046
Investing activities:
Purchase of property and equipment	(24,936)	(12,520)
Proceeds from asset dispositions	200	6,878
Purchase of short-term investments	(70,608)	(34,778)
Proceeds from sale of short-term investments	75,025	34,170
Deposits on aircraft	(419)	281
Net cash used in investing activities	(20,738)	(5,969)
Financing activities:
Proceeds from line of credit	2,400	5,669
Payments on line of credit	(10,000)	(21,790)
Repurchase of common stock	(1,037)
Net cash used in financing activities	(8,637)	(16,121)
Increase (decrease) in cash	728	(4,044)
Cash, beginning of period	2,849	5,091
Cash, end of period	3,577	1,047
Cash paid during the period for:
Interest	733	923
Income taxes	12	23
Noncash investing activities:
Other current liabilities and accrued payables related to purchase of property and equipment	$ 82	$ 165