Debt Obligations (Schedule of Long Term Obligations) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Total long term obligations	$ 364,481	$ 346,904
Less: current portion	(21,265)	(13,223)
Total long term obligations, net	343,216	333,681
Unsubordinated term loan [Member]
Debt Instrument [Line Items]
Total long term obligations	144,375	150,000
Revolving credit facility [Member]
Debt Instrument [Line Items]
Total long term obligations	143,000	106,000
Aircraft loans [Member]
Debt Instrument [Line Items]
Total long term obligations	63,156	70,754
Promissory note due to DHL, unsecured [Member]
Debt Instrument [Line Items]
Total long term obligations	$ 13,950	$ 20,150