Debt Obligations (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Nov. 06, 2013	Oct. 01, 2013	Dec. 31, 2012	Jul. 20, 2012
Debt Instrument [Line Items]
Long term obligations	$ 391,903,000			$ 364,481,000
Unsubordinated term loan and Revolving credit facility [Member]
Debt Instrument [Line Items]
Collateral coverage percentage	150.00%
Unsubordinated term loan [Member]
Debt Instrument [Line Items]
Variable interest rate	2.56%
Long term obligations	135,000,000			144,375,000
Revolving credit facility [Member]
Debt Instrument [Line Items]
Accordion feature amount			50,000,000		50,000,000
Increased borrowing capacity			275,000,000		225,000,000
Variable interest rate	2.56%
Credit facility, revolving credit loan, remaining borrowing capacity		74,100,000
Long term obligations	190,500,000			143,000,000
Letters of credit outstanding		10,400,000
Aircraft loans [Member]
Debt Instrument [Line Items]
Long term obligations	57,103,000			63,156,000
Collateralized property (in aircrafts)	6
Balloon payment percentage	20.00%
Variable interest rate, minimum	6.74%
Variable interest rate, maximum	7.36%
Promissory note due to DHL, unsecured [Member]
Debt Instrument [Line Items]
Long term obligations	9,300,000			13,950,000
Promissory note interest rate	5.00%
Prepayment of note per dollar of dividend distributed (in dollars per dividend)	0.20
Maximum [Member] | Unsubordinated term loan and Revolving credit facility [Member]
Debt Instrument [Line Items]
Maximum amount of common stock authorized for repurchase	$ 50,000,000