Reportable Segments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2013	Apr. 01, 2012	Mar. 31, 2013 item	Apr. 01, 2012	Sep. 30, 2012 item
Reportable Segments
Number of clients exceeding threshold			0		0
Revenue by client sector
Threshold percentage for disclosure of revenue from a single client			10.00%
Revenue	$ 641,999	$ 624,345	$ 1,300,544	$ 1,306,972
International
Revenue by client sector
Revenue	196,840	154,781	364,342	314,713
U.S. commercial
Revenue by client sector
Revenue	148,296	142,438	321,442	319,868
U.S. federal government
Revenue by client sector
Revenue	206,297	252,709	433,694	524,116
U.S. state and local government
Revenue by client sector
Revenue	$ 90,566	$ 74,417	$ 181,066	$ 148,275