Consolidated Statements of Income - USD ($) shares in Thousands	12 Months Ended
	Oct. 02, 2022	Oct. 03, 2021	Sep. 27, 2020
Revenue	$ 3,504,048,000	$ 3,213,513,000	$ 2,994,891,000
Gross profit	575,559,000	498,400,000	446,535,000
Selling, general and administrative expenses	(234,784,000)	(222,972,000)	(204,615,000)
Contingent consideration – fair value adjustments	(329,000)	3,273,000	14,971,000
Impairment of goodwill	0	0	(15,800,000)
Income from operations	340,446,000	278,701,000	241,091,000
Interest income	1,780,000	917,000	1,375,000
Interest expense	(13,364,000)	(12,748,000)	(14,475,000)
Other income	19,904,000	0	0
Income before income tax expense	348,766,000	266,870,000	227,991,000
Income tax expense	(85,602,000)	(34,039,000)	(54,101,000)
Net income	263,164,000	232,831,000	173,890,000
Net income attributable to noncontrolling interests	(39,000)	(21,000)	(31,000)
Net income attributable to Tetra Tech	263,125,000	232,810,000	173,859,000
Net income attributable to Tetra Tech	$ 263,125,000	$ 232,810,000	$ 173,859,000
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 4.91	$ 4.31	$ 3.21
Diluted (in dollars per share)	$ 4.86	$ 4.26	$ 3.16
Weighted-average common shares outstanding:
Basic (in shares)	53,620	54,078	54,235
Diluted (in shares)	54,163	54,675	55,022
Subcontractor costs
Costs of revenue	$ (668,468,000)	$ (661,341,000)	$ (646,319,000)
Other costs of revenue
Costs of revenue	$ (2,260,021,000)	$ (2,053,772,000)	$ (1,902,037,000)