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Quarterly Financial Information-Unaudited (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Oct. 01, 2017 | Jul. 02, 2017 | Apr. 02, 2017 | Jan. 01, 2017 | Oct. 02, 2016 | Jun. 26, 2016 | Mar. 27, 2016 | Dec. 27, 2015 | Oct. 01, 2017 | Oct. 02, 2016 | Sep. 27, 2015
Business acquisition |  |  |  |  |  |  |  |  |  |  |
Acquisition and integration expenses |  |  |  |  |  |  |  |  | $ 0 | $ 19,548 | $ 0
Revenue | $ 735,188 | $ 685,539 | $ 663,781 | $ 668,851 | $ 728,508 | $ 666,869 | $ 627,384 | $ 560,708 | 2,753,360 | 2,583,469 | 2,299,321
Operating income | 54,647 | 45,884 | 42,956 | 39,855 | 47,190 | 39,085 | 16,650 | 32,930 | 183,342 | 135,855 | 87,684
Net income attributable to Tetra Tech | $ 34,467 | $ 29,983 | $ 26,862 | $ 26,562 | $ 31,106 | $ 25,694 | $ 3,744 | $ 23,239 | $ 117,874 | $ 83,783 | $ 39,074
Earnings per share attributable to Tetra Tech: |  |  |  |  |  |  |  |  |  |  |
Basic (in dollars per share) | $ 0.61 | $ 0.52 | $ 0.47 | $ 0.47 | $ 0.54 | $ 0.44 | $ 0.06 | $ 0.39 | $ 2.07 | $ 1.44 | $ 0.64
Diluted (in dollars per share) | $ 0.60 | $ 0.52 | $ 0.46 | $ 0.46 | $ 0.53 | $ 0.44 | $ 0.06 | $ 0.39 | $ 2.04 | $ 1.42 | $ 0.64
Weighted-average common shares outstanding: |  |  |  |  |  |  |  |  |  |  |
Basic (in shares) | 56,338 | 57,184 | 57,270 | 57,099 | 57,309 | 57,796 | 58,451 | 59,058 | 56,911 | 58,186 | 60,913
Diluted (in shares) | 57,326 | 58,161 | 58,270 | 58,145 | 58,192 | 58,616 | 59,131 | 59,793 | 57,913 | 58,966 | 61,532
Coffey |  |  |  |  |  |  |  |  |  |  |
Business acquisition |  |  |  |  |  |  |  |  |  |  |
Acquisition and integration expenses |  |  |  |  | $ 2,600 | $ 1,000 | $ 15,900 |  |  | $ 19,500 |
Coffey | Interest expense |  |  |  |  |  |  |  |  |  |  |
Business acquisition |  |  |  |  |  |  |  |  |  |  |
Pre-payment charges paid |  |  |  |  |  |  | $ 1,900 |  |  | $ 1,900 |

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- Definition This element represents acquisition and integration -related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities. + References No definition available. + Details
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