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Regulatory - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Regulated Operations [Abstract] |  |  |
Comprehensive review period | 10 years |  |
Mid-term report period | 4 years |  |
Revenue from Title IV program funds | 71.50% | 72.30% | 74.80%

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- Definition Ninety by ten revenue test. + References No definition available. + Details
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