Quarterly Financial Information - Unaudited (Tables)

12 Months Ended

Sep. 27, 2020

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 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
Fiscal Year 2019
Revenue	$	717,431	$	722,621	$	825,793	$	841,502
Income from operations	55,711		47,545		64,841		20,665
Net income attributable to Tetra Tech	41,997		55,911		49,233		11,527
Earnings per share attributable to Tetra Tech:
Basic	$	0.76	$	1.01	$	0.90	$	0.21
Diluted	$	0.75	$	1.00	$	0.88	$	0.21
Weighted-average common shares outstanding:
Basic	55,390		55,143		54,819		54,617
Diluted	56,366		55,985		55,768		55,618