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Effect of Increase in Cost of Insurance and Claims (Detail) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 30, 2017 | Sep. 30, 2017 | Jul. 01, 2017 | Apr. 01, 2017 | Dec. 31, 2016 | Sep. 24, 2016 | Jun. 25, 2016 | Mar. 26, 2016 | Dec. 30, 2017 | Dec. 31, 2016 | Dec. 26, 2015
Change in Accounting Estimate [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating income | $ 70,049 |  | $ 60,567 |  | $ 61,018 |  | $ 52,334 |  | $ 63,765 |  | $ 58,461 |  | $ 53,093 |  | $ 47,932 |  | $ 243,968 | $ 223,251 | $ 241,706
Net income attributable to Landstar System, Inc. and subsidiary | $ 64,752 |  | $ 42,443 |  | $ 37,510 |  | $ 32,383 |  |  |  |  |  |  |  |  |  | $ 177,088 | $ 137,350 | $ 147,689
Earnings per share attributable to Landstar System, Inc. and subsidiary | $ 1.54 | [1] | $ 1.01 | [1] | $ 0.89 | [1] | $ 0.77 | [1] | $ 0.95 | [1] | $ 0.86 | [1] | $ 0.77 | [1] | $ 0.69 | [1] | $ 4.22 | $ 3.26 | $ 3.38
Diluted earnings per share attributable to Landstar System, Inc. and subsidiary | $ 1.54 | [1] | $ 1.01 | [1] | $ 0.89 | [1] | $ 0.77 | [1] | $ 0.94 | [1] | $ 0.86 | [1] | $ 0.76 | [1] | $ 0.69 | [1] | $ 4.21 | $ 3.25 | $ 3.37
Development of Prior Year Self Insured Claims Estimates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in Accounting Estimate [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,144 | $ 1,079 | $ 4,852
Net income attributable to Landstar System, Inc. and subsidiary |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,578 | $ 667 | $ 2,999
Earnings per share attributable to Landstar System, Inc. and subsidiary |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.06 | $ 0.02 | $ 0.07
Diluted earnings per share attributable to Landstar System, Inc. and subsidiary |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.06 | $ 0.02 | $ 0.07
[1] | Due to the changes in the number of average common shares and common stock equivalents outstanding during the year, the sum of earnings per share amounts for each quarter do not necessarily sum in the aggregate to the earnings per share amounts for the full year.

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