Business Segment Information - Sales and Gross profit (Details) $ in Millions	3 Months Ended	6 Months Ended
Nov. 30, 2019 USD ($)	Nov. 30, 2018 USD ($)	Nov. 30, 2019 USD ($) segment	Nov. 30, 2018 USD ($)
Disaggregation of revenue by major customer markets
Operating segments (in segments) \| segment			2
Sales	$ 560.9	$ 493.3	$ 1,102.4	$ 959.6
Gross profit	85.9	78.3	167.5	149.5
Aviation Services
Disaggregation of revenue by major customer markets
Sales	532.0	462.9	1,043.8	901.3
Gross profit	85.7	74.9	165.7	142.0
Expeditionary Services
Disaggregation of revenue by major customer markets
Sales	28.9	30.4	58.6	58.3
Gross profit	$ 0.2	$ 3.4	$ 1.8	$ 7.5

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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-Publisher FASB
-Name Accounting Standards Codification
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