Significant Customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Concentration Risk [Line Items]
Accounts receivable	$ 36,663		$ 36,663		$ 43,513
DHL [Member] | Revenues from Leases and Contracted Services [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of consolidated revenues	48.00%	57.00%	50.00%	57.00%
DHL [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 9,000		$ 9,000		12,200
US Military [Member] | Revenues from Services Performed [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of consolidated revenues	18.00%	17.00%	17.00%	16.00%
US Military [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 5,300		$ 5,300		$ 6,000