Significant Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Concentration Risk [Line Items]
Accounts receivable	$ 39,160		$ 39,160		$ 43,513
DHL [Member] | Revenues from Leases and Contracted Services [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of consolidated revenues	47.00%	54.00%	49.00%	56.00%
DHL [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 5,600		$ 5,600		12,200
US Military [Member] | Revenues from Services Performed [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of consolidated revenues	17.00%	17.00%	17.00%	17.00%
US Military [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 7,400		$ 7,400		$ 6,000