Fair Value of Financial Instruments - Discount Rate (Details) - Discount Rates	Apr. 30, 2020
Valuation, Income Approach | Education
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Reporting unit, measurement input	0.100
Valuation, Income Approach | Aviation
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Reporting unit, measurement input	0.105
Valuation, Income Approach | Technical Solutions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Reporting unit, measurement input	0.110
Valuation, Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Reporting unit, measurement input	0.150