Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Oct. 02, 2022	Oct. 03, 2021	Sep. 27, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 263,164	$ 232,831	$ 173,890
Other comprehensive income, net of tax
Foreign currency translation adjustments, net of tax	(94,933)	30,644	3,435
Gain (loss) on cash flow hedge valuations, net of tax	11,806	6,117	(4,638)
Other comprehensive income (loss), net of tax	(83,127)	36,761	(1,203)
Comprehensive income, net of tax	180,037	269,592	172,687
Comprehensive income attributable to noncontrolling interests, net of tax	28	24	30
Comprehensive income attributable to Tetra Tech, net of tax	$ 180,009	$ 269,568	$ 172,657