Business Segment And Geographic Area Information (Contracts Exceeding 10% Of Other Income 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
Operating income	$ 53,823	$ 58,508	$ 59,168	$ 55,855	$ 58,864	$ 54,515	$ 56,529	$ 45,232	$ 227,354	$ 215,140	$ 179,079
Total operating income, percentage									100.00%	100.00%	100.00%
U S Army Contract A [Member]
Operating Income									39,432	22,748	21,077
Operating income, percentage									17.30%	10.60%	11.80%
All Other Contracts [Member]
Operating Income									$ 187,922	$ 192,392	$ 158,002
Operating Income, percentage									82.70%	89.40%	88.20%