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Quarterly Financial Information-Unaudited (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Jul. 01, 2018 | Apr. 01, 2018 | Dec. 31, 2017 | Oct. 01, 2017 | Jul. 02, 2017 | Apr. 02, 2017 | Jan. 01, 2017 | Sep. 30, 2018 | Oct. 01, 2017 | Oct. 02, 2016
Business acquisition |  |  |  |  |  |  |  |  |  |  |
Deferred tax benefit from tax reform remeasurement |  |  |  | $ 14,700 |  |  |  |  | $ 14,700 |  |
Decrease in revenue related to construction settlement | $ 10,600 |  |  |  |  |  |  |  |  |  |
Loss from construction settlement claim | 12,500 |  |  |  |  |  |  |  |  |  |
Revenue | 739,343 | $ 764,795 | $ 700,262 | 759,749 | $ 735,188 | $ 685,539 | $ 663,781 | $ 668,851 | 2,964,148 | $ 2,753,360 | $ 2,583,469
Income from operations | 43,285 | 55,496 | 42,716 | 48,589 | 54,647 | 45,884 | 42,956 | 39,855 | 190,086 | 183,342 | 135,855
Net income attributable to Tetra Tech | $ 28,802 | $ 33,322 | $ 28,725 | $ 46,034 | $ 34,467 | $ 29,983 | $ 26,862 | $ 26,562 | $ 136,883 | $ 117,874 | $ 83,783
Earnings per share attributable to Tetra Tech: |  |  |  |  |  |  |  |  |  |  |
Basic (in dollars per share) | $ 0.52 | $ 0.60 | $ 0.51 | $ 0.82 | $ 0.61 | $ 0.52 | $ 0.47 | $ 0.47 | $ 2.46 | $ 2.07 | $ 1.44
Diluted (in dollars per share) | $ 0.51 | $ 0.59 | $ 0.51 | $ 0.81 | $ 0.60 | $ 0.52 | $ 0.46 | $ 0.46 | $ 2.42 | $ 2.04 | $ 1.42
Weighted-average common shares outstanding: |  |  |  |  |  |  |  |  |  |  |
Basic (in shares) | 55,341 | 55,537 | 55,841 | 55,855 | 56,338 | 57,184 | 57,270 | 57,099 | 55,670 | 56,911 | 58,186
Diluted (in shares) | 56,349 | 56,390 | 56,673 | 56,875 | 57,326 | 58,161 | 58,270 | 58,145 | 56,598 | 57,913 | 58,966
Disposed of by Sale | Non-core field services business |  |  |  |  |  |  |  |  |  |  |
Business acquisition |  |  |  |  |  |  |  |  |  |  |
Loss on disposition of business |  | $ 3,400 |  |  |  |  |  |  | $ 3,400 |  |

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