Business Segment Information - Sales and Gross Profit (Details) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2022 USD ($)	Nov. 30, 2021 USD ($)	Nov. 30, 2022 USD ($) segment	Nov. 30, 2021 USD ($)
Disaggregation of revenue by major customer markets
Operating segments (in segments) | segment			2
Net sales	$ 469.8	$ 436.6	$ 916.1	$ 891.7
Gross profit	85.8	78.4	167.7	143.0
Aviation Services
Disaggregation of revenue by major customer markets
Net sales	445.7	419.3	869.7	854.9
Gross profit	82.3	74.0	160.3	134.9
Expeditionary Services
Disaggregation of revenue by major customer markets
Net sales	24.1	17.3	46.4	36.8
Gross profit	$ 3.5	$ 4.4	$ 7.4	$ 8.1