Quarterly Financial Information - Unaudited (Tables)

12 Months Ended

Sep. 29, 2019

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 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
Fiscal Year 2018
Revenue	$	759,749	$	700,262	$	764,795	$	739,343
Income from operations	48,589		42,716		55,496		43,285
Net income attributable to Tetra Tech	46,034		28,725		33,322		28,802
Earnings per share attributable to Tetra Tech:
Basic	$	0.82	$	0.51	$	0.60	$	0.52
Diluted	$	0.81	$	0.51	$	0.59	$	0.51
Weighted-average common shares outstanding:
Basic	55,855		55,841		55,537		55,341
Diluted	56,875		56,673		56,390		56,349