Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 02, 2023	Apr. 03, 2022	Apr. 02, 2023	Apr. 03, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 42,841	$ 53,049	$ 159,556	$ 121,548
Other comprehensive income, net of tax
Foreign currency translation adjustment, net of tax	(8,154)	2,807	24,953	2,121
Gain (loss) on cash flow hedge valuations, net of tax	(896)	4,938	(985)	7,604
Net pension adjustments	2,794	0	2,794	0
Other comprehensive income (loss), net of tax	(6,256)	7,745	26,762	9,725
Comprehensive income, net of tax	36,585	60,794	186,318	131,273
Comprehensive income attributable to noncontrolling interests, net of tax	10	10	19	19
Comprehensive income attributable to Tetra Tech, net of tax	$ 36,575	$ 60,784	$ 186,299	$ 131,254