Summary of Significant Accounting Policies - Goodwill (Details) $ in Millions	12 Months Ended
	May 31, 2023 USD ($) item	May 31, 2022 USD ($)
Goodwill
Number of reporting units | item	3
Goodwill impairment charges	$ 0.0
Goodwill, beginning balance	116.4	$ 119.3
Trax acquisition	48.5
Foreign currency translation adjustments	(1.1)	(2.9)
Goodwill, ending balance	$ 175.8	116.4
Aviation Services
Goodwill
Number of reporting units | item	2
Goodwill, beginning balance	$ 97.6	100.5
Trax acquisition	60.5
Foreign currency translation adjustments	(1.1)	(2.9)
Goodwill, ending balance	$ 157.0	97.6
Expeditionary Services
Goodwill
Number of reporting units | item	1
Goodwill, beginning balance	$ 18.8	18.8
Goodwill, ending balance	$ 18.8	$ 18.8