Earnings per Share ("EPS") - Summary of Number of Weighted-Average Shares Used to Compute Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |
3 Months Ended | 9 Months Ended | ||
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Jun. 28, 2026 |
Jun. 29, 2025 |
Jun. 28, 2026 |
Jun. 29, 2025 |
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| Earnings Per Share [Abstract] | ||||
| Net income attributable to Tetra Tech | $ 109,584 | $ 113,844 | $ 308,235 | $ 119,979 |
| Net income attributable to Tetra Tech | $ 109,584 | $ 113,844 | $ 308,235 | $ 119,979 |
| Weighted-average common shares outstanding – basic (in shares) | 258,151 | 263,026 | 259,685 | 265,589 |
| Effect of dilutive stock options and unvested restricted stock (in shares) | 1,628 | 1,829 | 1,774 | 1,900 |
| Shares issuable assuming conversion of convertible notes (in shares) | 0 | 0 | 0 | 624 |
| Weighted-average common stock outstanding – diluted (in shares) | 259,779 | 264,855 | 261,459 | 268,113 |
| Earnings per share attributable to Tetra Tech: | ||||
| Basic (in dollars per share) | $ 0.42 | $ 0.43 | $ 1.19 | $ 0.45 |
| Diluted (in dollars per share) | $ 0.42 | $ 0.43 | $ 1.18 | $ 0.45 |
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- Definition Earnings Per Share, Basic and Diluted EPS No definition available.
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- References No definition available.
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- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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