Condensed Consolidating Financial Information Guarantor - Subsidiaries (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Consolidating Statements of Cash Flows
Net cash provided by operating activities	$ 50,550	$ 30,352	$ 76,857
Investing activities:
Purchase of property and equipment	(128,475)	(91,028)	(98,230)
Proceeds from asset dispositions	11,302	6,852	1,171
Purchase of short-term investments	(216,265)	(234,631)	(450,188)
Proceeds from sale of short-term investments	249,041	282,743	375,517
Deposits on aircraft	(6,217)	(7,798)	(3,780)
Loan to unconsolidated affiliate	(975)
Other investments	(50)
Net cash used in investing activities	(91,639)	(43,862)	(175,510)
Financing activities:
Repurchase of common stock	(1,861)
Proceeds from issuance of Senior Notes due 2018			300,000
Premium and costs to retire debt early			(7,667)
Repayment of Senior Notes due 2013			(200,000)
Debt issuance costs			(5,322)
Proceeds from line of credit	127,323	73,865	59,287
Payments on line of credit	(86,615)	(58,892)	(46,518)
Net cash provided by financing activities	38,847	14,973	99,780
(Decrease) increase in cash	(2,242)	1,463	1,127
Cash, beginning of year	5,091	3,628	2,501
Cash, end of year	2,849	5,091	3,628
Parent Company Only (issuer) [Member]
Condensed Consolidating Statements of Cash Flows
Net cash provided by operating activities	49,031	30,245	74,648
Investing activities:
Purchase of property and equipment	(128,475)	(91,028)	(95,869)
Proceeds from asset dispositions	11,302	6,852	1,171
Purchase of short-term investments	32,776		(74,671)
Proceeds from sale of short-term investments		48,112
Deposits on aircraft	(6,217)	(7,798)	(3,780)
Loan to unconsolidated affiliate	(975)
Other investments	(50)
Net cash used in investing activities	(91,639)	(43,862)	(173,149)
Financing activities:
Repurchase of common stock	(1,861)
Proceeds from issuance of Senior Notes due 2018			300,000
Premium and costs to retire debt early			(7,667)
Repayment of Senior Notes due 2013			(200,000)
Debt issuance costs			(5,322)
Proceeds from line of credit	127,323	73,865	59,287
Payments on line of credit	(86,615)	(58,892)	(46,518)
Net cash provided by financing activities	38,847	14,973	99,780
(Decrease) increase in cash	(3,761)	1,356	1,279
Cash, beginning of year	4,313	2,957	1,678
Cash, end of year	552	4,313	2,957
Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Cash Flows
Net cash provided by operating activities	1,519	107	2,209
Investing activities:
Purchase of property and equipment			(2,361)
Proceeds from asset dispositions
Purchase of short-term investments
Deposits on aircraft
Loan to unconsolidated affiliate
Other investments
Net cash used in investing activities			(2,361)
Financing activities:
Repurchase of common stock
Proceeds from line of credit
Payments on line of credit
Net cash provided by financing activities
(Decrease) increase in cash	1,519	107	(152)
Cash, beginning of year	778	671	823
Cash, end of year	2,297	778	671
Eliminations [Member]
Condensed Consolidating Statements of Cash Flows
Net cash provided by operating activities
Investing activities:
Purchase of property and equipment
Proceeds from asset dispositions
Purchase of short-term investments
Deposits on aircraft
Loan to unconsolidated affiliate
Other investments
Net cash used in investing activities
Financing activities:
Repurchase of common stock
Proceeds from line of credit
Payments on line of credit
Net cash provided by financing activities
(Decrease) increase in cash
Cash, beginning of year	0
Cash, end of year	$ 0