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Description of Business, Basis of Presentation, and Significant Accounting Policies (Details) (USD $)
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12 Months Ended |
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May 31, 2014
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May 31, 2013
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May 31, 2012
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| Accounting Policies [Abstract] |
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| Disclosure on geographic areas, Description of revenue from external customers |
revenue within Germany, which represented less than one percent of the Company's total revenue
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revenue within Germany, which represented less than one percent of the Company's total revenue
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revenue within Germany, which represented less than one percent of the Company's total revenue
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| Disclosure on geographic areas, Long-lived assets |
Long-lived assets in Germany are insignificant in relation to total long-lived assets of the Company
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Long-lived assets in Germany are insignificant in relation to total long-lived assets of the Company
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| Minimum period in which payroll taxes are typically remitted after receipt of collections from client |
1 day
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| Maximum period in which payroll taxes are typically remitted after receipt of collections from client |
30 days
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| Maximum Days in Which Payroll Taxes Will Be Remitted After Receipt Of Collections From Client |
90 days
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| Allowance for doubtful accounts |
$ 1,500,000
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$ 1,000,000
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| Direct costs billed and incurred |
3,400,000,000
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3,000,000,000
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3,300,000,000
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| Maximum individual workers' compensation claims liability |
1,000,000
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1,000,000
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| Maximum Individual Claims Liability Health Insurance |
300,000
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| Workers' compensation insurance costs in current liabilities |
8,500,000
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6,800,000
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| Workers' compensation insurance costs in long-term liabilities |
16,000,000
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13,700,000
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| Reserve for uncertain tax positions |
$ 29,800,000
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$ 19,800,000
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Software Development [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
15 years
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Minimum [Member]
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| Property, Plant and Equipment [Line Items] |
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| Finite-Lived Intangible Asset, Useful Life |
3 years
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Minimum [Member] | Building and Building Improvements [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
10 years
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Minimum [Member] | Data Processing Equipment [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
3 years
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Minimum [Member] | Furniture Fixtures And Equipment [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
5 years
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Minimum [Member] | Software and Software Development Costs [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
3 years
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Maximum [Member]
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| Property, Plant and Equipment [Line Items] |
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| Finite-Lived Intangible Asset, Useful Life |
12 years
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Maximum [Member] | Building and Building Improvements [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
35 years
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Maximum [Member] | Data Processing Equipment [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
5 years
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Maximum [Member] | Furniture Fixtures And Equipment [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
7 years
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Maximum [Member] | Leasehold Improvements [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
10 years
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Maximum [Member] | Software and Software Development Costs [Member]
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| Property, Plant and Equipment [Line Items] |
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| Property, Plant and Equipment, Useful Life |
5 years
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