Business Segment Information - Customers Percentage of Sales (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2020	May 31, 2019	May 31, 2018
Business Segment Information
Net sales	$ 416.5	$ 553.1	$ 560.9	$ 541.5	$ 562.7	$ 529.5	$ 493.3	$ 466.3	$ 2,072.0	$ 2,051.8	$ 1,748.3
U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales									$ 668.2	$ 546.2	$ 304.3
Percentage of total sales									32.20%	26.60%	17.40%
Aviation Services
Business Segment Information
Net sales									$ 1,964.2	$ 1,920.6	$ 1,635.8
Aviation Services | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales									588.7	455.9	241.3
Expeditionary Services
Business Segment Information
Net sales									107.8	131.2	112.5
Expeditionary Services | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales									$ 79.5	$ 90.3	$ 63.0