Consolidated Statements of Income (USD $) In Thousands, except Per Share data	12 Months Ended
	Oct. 02, 2011	Oct. 03, 2010	Sep. 27, 2009
Revenue	$ 2,573,144	$ 2,201,232	$ 2,287,484
Subcontractor costs	(780,817)	(741,002)	(901,347)
Other costs of revenue	(1,462,172)	(1,172,542)	(1,108,512)
Selling, general and administrative expenses	(183,733)	(163,214)	(155,736)
Operating income	146,422	124,474	121,889
Interest income	879	801	554
Interest expense	(6,809)	(2,188)	(3,238)
Income before income tax expense	140,492	123,087	119,205
Income tax expense	(47,510)	(46,268)	(32,177)
Net income including noncontrolling interests	92,982	76,819	87,028
Net income attributable to noncontrolling interests	(2,943)
Net income attributable to Tetra Tech	$ 90,039	$ 76,819	$ 87,028
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.45	$ 1.25	$ 1.45
Diluted (in dollars per share)	$ 1.43	$ 1.24	$ 1.43
Weighted-average common shares outstanding
Basic (in shares)	62,053	61,430	60,135
Diluted (in shares)	62,775	62,087	60,994