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Mergers and Acquisitions - Pro-Forma Operating Results (Details) - Coffey and INDUS - USD ($) $ / shares in Units, $ in Thousands | 9 Months Ended
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Jul. 02, 2017 | Jun. 26, 2016
Mergers and Acquisitions |  |
Revenue | $ 2,018,171 | $ 1,986,149
Operating income | 128,695 | 102,855
Net income attributable to Tetra Tech | $ 83,407 | $ 65,923
Earnings per share attributable to Tetra Tech, Basic (in dollars per share) | $ 1.46 | $ 1.12
Earnings per share attributable to Tetra Tech, Diluted (in dollars per share) | $ 1.44 | $ 1.11

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- Definition The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(2)-(3) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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