Debt Obligations (Schedule of Long Term Obligations) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Total long term obligations	$ 384,515	$ 364,481
Less: current portion	(23,721)	(21,265)
Total long term obligations, net	360,794	343,216
Unsubordinated term loan [Member]
Debt Instrument [Line Items]
Total long term obligations	131,250	144,375
Revolving credit facility [Member]
Debt Instrument [Line Items]
Total long term obligations	190,500	143,000
Aircraft loans [Member]
Debt Instrument [Line Items]
Total long term obligations	55,015	63,156
Promissory note due to DHL, unsecured [Member]
Debt Instrument [Line Items]
Total long term obligations	$ 7,750	$ 13,950