Reportable Segments (Details) (USD $)	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Jul. 01, 2012	Apr. 01, 2012	Jan. 01, 2012	Oct. 02, 2011	Jul. 03, 2011	Apr. 03, 2011	Jan. 02, 2011	Sep. 30, 2012	Oct. 02, 2011	Oct. 03, 2010
Financial information concerning reportable segments
Revenue	$ 719,405,000	$ 684,698,000	$ 624,345,000	$ 682,627,000	$ 675,662,000	$ 673,792,000	$ 612,566,000	$ 611,124,000	$ 2,711,075,000	$ 2,573,144,000	$ 2,201,232,000
Operating income	48,470,000	46,261,000	35,543,000	36,093,000	43,433,000	39,408,000	29,256,000	34,325,000	166,367,000	146,422,000	124,474,000
Depreciation									26,651,000	27,138,000	20,402,000
Total assets	1,671,030,000				1,593,988,000				1,671,030,000	1,593,988,000
Engineering and consulting services (ECS)
Financial information concerning reportable segments
Revenue									1,036,588,000	930,067,000	536,384,000
Operating income									88,091,000	88,135,000	48,582,000
Depreciation									8,887,000	10,786,000	5,503,000
Total assets	877,919,000				767,347,000				877,919,000	767,347,000
Technical support services (TSS)
Financial information concerning reportable segments
Revenue									919,862,000	867,130,000	829,231,000
Operating income									67,411,000	59,113,000	54,822,000
Depreciation									2,801,000	2,822,000	2,199,000
Total assets	558,575,000				505,198,000				558,575,000	505,198,000
Engineering and architecture services (EAS)
Financial information concerning reportable segments
Revenue									318,755,000	308,112,000	294,112,000
Operating income									12,485,000	22,597,000	12,194,000
Depreciation									1,665,000	1,814,000	2,100,000
Total assets	113,201,000				111,555,000				113,201,000	111,555,000
Remediation and construction management (RCM)
Financial information concerning reportable segments
Revenue									621,957,000	604,651,000	651,595,000
Operating income									22,374,000	13,183,000	30,243,000
Depreciation									10,233,000	8,775,000	7,850,000
Total assets	310,991,000				296,361,000				310,991,000	296,361,000
Elimination of inter-segment revenue
Financial information concerning reportable segments
Revenue									(186,087,000)	(136,816,000)	(110,090,000)
Corporate
Financial information concerning reportable segments
Operating income									(23,994,000)	(36,606,000)	(21,367,000)
Depreciation									3,065,000	2,941,000	2,750,000
Amortization of intangibles									(29,600,000)	(28,000,000)	(12,700,000)
Fair value adjustments to contingent consideration liabilities	19,246,000				1,755,000				19,246,000	1,755,000	265,000
Assets not allocated to segments and intercompany eliminations
Financial information concerning reportable segments
Total assets	$ (189,656,000)				$ (86,473,000)				$ (189,656,000)	$ (86,473,000)