Condensed Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Jan. 01, 2012	Jan. 02, 2011
Revenue	$ 682,627	$ 611,124
Subcontractor costs	(190,571)	(205,544)
Other costs of revenue	(407,336)	(329,927)
Selling, general and administrative expenses	(48,627)	(41,328)
Operating income	36,093	34,325
Interest expense - net	(1,311)	(1,305)
Income before income tax expense	34,782	33,020
Income tax expense	(12,079)	(10,266)
Net income including noncontrolling interests	22,703	22,754
Net income attributable to noncontrolling interests	(93)	(453)
Net income attributable to Tetra Tech	$ 22,610	$ 22,301
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.36	$ 0.36
Diluted (in dollars per share)	$ 0.36	$ 0.36
Weighted-average common shares outstanding:
Basic (in shares)	62,433	61,665
Diluted (in shares)	63,068	62,443