Business Segment Information - Customers Percentage of Sales (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2021
Business Segment Information
Net sales	$ 1,990.5	$ 1,820.0	$ 1,652.3
U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales	577.0	620.0	738.8
Aviation Services
Business Segment Information
Net sales	1,898.7	1,745.8	1,553.7
Aviation Services | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales	499.7	557.4	657.0
Aviation Services | Commercial
Business Segment Information
Net sales	1,320.5	1,081.6	793.9
Aviation Services | Government and defense
Business Segment Information
Net sales	578.2	664.2	759.8
Expeditionary Services
Business Segment Information
Net sales	91.8	74.2	98.6
Expeditionary Services | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales	77.3	62.6	81.8
Expeditionary Services | Commercial
Business Segment Information
Net sales	8.3	2.2	12.5
Expeditionary Services | Government and defense
Business Segment Information
Net sales	$ 83.5	$ 72.0	$ 86.1
Customer | Total sales | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Percentage of total sales	29.00%	34.10%	44.70%