Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 29, 2020	Mar. 31, 2019	Mar. 29, 2020	Mar. 31, 2019
Revenue	$ 734,133	$ 722,621	$ 1,531,756	$ 1,440,052
Gross profit	97,000	96,471	206,737	195,155
Selling, general and administrative expenses	(51,041)	(48,898)	(97,476)	(91,871)
Contingent consideration – fair value adjustments	1,571	(28)	1,571	(28)
Income from operations	47,530	47,545	110,832	103,256
Interest expense	(3,501)	(3,164)	(6,849)	(6,061)
Income before income tax (expense) benefit	44,029	44,381	103,983	97,195
Income tax (expense) benefit	(7,616)	11,563	(20,253)	781
Net income	36,413	55,944	83,730	97,976
Net income attributable to noncontrolling interests	(16)	(33)	(23)	(69)
Net income attributable to Tetra Tech	$ 36,397	$ 55,911	$ 83,707	$ 97,907
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.67	$ 1.01	$ 1.53	$ 1.77
Diluted (in dollars per share)	$ 0.66	$ 1.00	$ 1.51	$ 1.74
Weighted-average common shares outstanding:
Basic (in shares)	54,699	55,143	54,541	55,237
Diluted (in shares)	55,463	55,985	55,380	56,161
Subcontractor costs
Cost of revenue	$ (149,673)	$ (137,237)	$ (333,274)	$ (301,305)
Other costs of revenue
Cost of revenue	$ (487,460)	$ (488,913)	$ (991,745)	$ (943,592)