Quarterly Financial Information - Unaudited (Tables)

12 Months Ended

Oct. 03, 2021

Quarterly Financial Information Disclosure [Abstract]

Schedule of unaudited quarterly data

	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(in thousands, except per share data)
Fiscal Year 2021
Revenue	$	765,104	$	754,764	$	801,633	$	892,012
Income from operations	66,252		60,807		69,807		81,836
Net income attributable to Tetra Tech	52,436		45,517		51,903		82,954
Earnings per share attributable to Tetra Tech:
Basic	$	0.97	$	0.84	$	0.96	$	1.54
Diluted	$	0.96	$	0.83	$	0.95	$	1.52
Weighted-average common shares outstanding:
Basic	53,927		54,187		54,117		54,019
Diluted	54,637		54,736		54,666		54,597
Fiscal Year 2020
Revenue	$	797,623	$	734,133	$	709,771	$	753,364
Income from operations	63,302		47,530		63,525		66,735
Net income attributable to Tetra Tech	47,310		36,397		45,497		44,654
Earnings per share attributable to Tetra Tech:
Basic	$	0.87	$	0.67	$	0.84	$	0.83
Diluted	$	0.85	$	0.66	$	0.83	$	0.82
Weighted-average common shares outstanding:
Basic	54,560		54,699		53,985		53,841
Diluted	55,438		55,463		54,692		54,603