Derivative Instruments and Hedging Activities (Details) In Thousands, unless otherwise specified	Sep. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2011 Foreign currency forward contracts Italy Aerial operations USD ($)	Dec. 31, 2011 Foreign currency forward contracts Italy Aerial operations EUR (€)	Dec. 31, 2011 Foreign currency forward contracts Greece Aerial operations USD ($)	Dec. 31, 2011 Foreign currency forward contracts Greece Aerial operations EUR (€)	Sep. 30, 2012 Foreign currency forward contracts Australia Aerial operations USD ($)	Sep. 30, 2012 Foreign currency forward contracts Australia Aerial operations AUD	Dec. 31, 2011 Foreign currency forward contracts Australia Aerial operations USD ($)	Dec. 31, 2011 Foreign currency forward contracts Australia Aerial operations AUD	Sep. 30, 2012 Foreign currency forward contracts Europe Aerial operations USD ($)	Sep. 30, 2012 Foreign currency forward contracts Europe Aerial operations EUR (€)	Sep. 30, 2012 Foreign currency forward contracts Canada Aerial operations USD ($)	Sep. 30, 2012 Foreign currency forward contracts Canada Aerial operations CAD
Derivative Instruments and Hedging Activities
Contract Value	$ 16,136	$ 39,154	$ 3,948	€ 2,848	$ 18,789	€ 13,718	$ 8,474	8,698	$ 16,417	17,848	$ 5,919	€ 4,253	$ 1,743	1,755
Market Value	16,166	39,238	3,702		17,790		8,910		17,746		5,475		1,781
Asset (Liability)	$ (30)	$ (84)	$ 246		$ 999		$ (436)		$ (1,329)		$ 444		$ (38)