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International Risk Factors (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2015 USD ($) | Mar. 31, 2018 USD ($) item | Mar. 31, 2017 USD ($) | Jun. 30, 2010 item
International Risk Factors |  |  |  |  |  |
Foreign currency gains (losses) | $ | $ 0.2 | $ (0.6) |  | $ (1.4) | $ (2.0) |
Venezuela |  |  |  |  |  |
International Risk Factors |  |  |  |  |  |
Number of rigs expropriated by Venezuelan government | item |  |  |  |  |  | 11
Argentina |  |  |  |  |  |
International Risk Factors |  |  |  |  |  |
Foreign currency gains (losses) | $ |  |  | $ (8.5) |  |  |
Operating revenues | Geographic concentration risk | South America |  |  |  |  |  |
International Risk Factors |  |  |  |  |  |
Concentration percentage |  |  |  | 95.80% |  |
Minimum |  |  |  |  |  |
International Risk Factors |  |  |  |  |  |
Number of geographical areas of operation to minimize risks | item |  |  |  | 1 |  |
Contract Drilling: | Operating revenues | Geographic concentration risk | International locations |  |  |  |  |  |
International Risk Factors |  |  |  |  |  |
Concentration percentage |  |  |  | 10.10% |  |

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