Business Segment Information (Details) $ in Millions	3 Months Ended	6 Months Ended
Nov. 30, 2018 USD ($)	Nov. 30, 2017 USD ($)	Nov. 30, 2018 USD ($) segment	Nov. 30, 2017 USD ($)
Business Segment Information
Number of business segments \| segment			2
Sales	$ 493.3	$ 420.6	$ 959.6	$ 818.5
Gross profit:	78.3	70.7	149.5	132.3
Aviation Services
Business Segment Information
Sales	462.9	391.7	901.3	763.0
Gross profit:	74.9	66.0	142.0	123.8
Expeditionary Services
Business Segment Information
Sales	30.4	28.9	58.3	55.5
Gross profit:	$ 3.4	$ 4.7	$ 7.5	$ 8.5

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

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-Name Accounting Standards Codification
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 606
-SubTopic 10
-Section 50
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