Earnings per Share (Tables)

12 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Schedule of number of weighted-average shares used to compute basic and diluted EPS

The following table sets forth the number of weighted-average shares used to compute basic and diluted EPS:

	Fiscal Year Ended
	September 30, 2018		October 1, 2017		October 2, 2016
	(in thousands, except per share data)
Net income attributable to Tetra Tech	$	136,883	$	117,874	$	83,783
Weighted-average common shares outstanding – basic	55,670		56,911		58,186
Effect of diluted stock options and unvested restricted stock	928		1,002		780
Weighted-average common stock outstanding – diluted	56,598		57,913		58,966
Earnings per share attributable to Tetra Tech:
Basic	$	2.46	$	2.07	$	1.44
Diluted	$	2.42	$	2.04	$	1.42