Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jul. 03, 2022	Jun. 27, 2021	Jul. 03, 2022	Jun. 27, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 58,657	$ 51,924	$ 180,205	$ 149,900
Other comprehensive income, net of tax
Foreign currency translation adjustment, net of tax	(44,884)	11,159	(42,763)	54,527
Gain on cash flow hedge valuations, net of tax	2,380	1,498	9,984	4,864
Other comprehensive income (loss), net of tax	(42,504)	12,657	(32,779)	59,391
Comprehensive income, net of tax	16,153	64,581	147,426	209,291
Comprehensive income attributable to noncontrolling interests, net of tax	6	23	25	50
Comprehensive income attributable to Tetra Tech, net of tax	$ 16,147	$ 64,558	$ 147,401	$ 209,241