CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating activities:
Net earnings	$ 28,354	$ 8,232
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	20,863	16,782
Deferred income taxes	18,905	5,338
Equity in loss of unconsolidated affiliate	1,083
Gain on asset dispositions	(14,676)	(690)
Impairment of assets	421
Other	(70)	406
Changes in operating assets and liabilities	2,826	(5,186)
Net cash provided by operating activities	57,706	24,882
Investing activities:
Purchase of property and equipment	(50,004)	(32,407)
Proceeds from asset dispositions	37,255	8,587
Purchase of short-term investments	(246,375)	(102,436)
Proceeds from sale of short-term investments	220,249	94,842
Deposits returned on aircraft	3,150
Deposits paid on aircraft	(571)	(9,126)
Net cash used in investing activities	(36,296)	(40,540)
Financing activities:
Proceeds from line of credit	41,965	66,081
Payments on line of credit	(52,997)	(54,090)
Repurchase of common stock for payroll tax withholding requirements	(1,037)
Net cash (used in) provided by financing activities	(12,069)	11,991
Increase (decrease) in cash	9,341	(3,667)
Cash, beginning of period	2,849	5,091
Cash, end of period	12,190	1,424
Cash paid during the period for:
Interest	14,286	14,317
Income taxes	229	563
Noncash investing activities:
Other current liabilities and accrued payables related to purchase of property and equipment	$ 367	$ 1,300