Business Segment And Geographic Area Information (Contracts Exceeding 10% Of Revenue From External Customers) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues	$ 681,838	$ 734,607	$ 752,673	$ 700,864	$ 697,916	$ 656,954	$ 661,611	$ 587,557	$ 2,869,982	$ 2,604,038	$ 2,020,334
Total revenues, percentage									100.00%	100.00%	100.00%
U S Army Contract A [Member]
Revenues									487,615	318,615	407,656
Revenues, percentage									17.00%	12.20%	20.20%
All Other Contracts [Member]
Revenues									$ 2,382,367	$ 2,285,423	$ 1,612,678
Revenues, percentage									83.00%	87.80%	79.80%