Business Segment Information - Customers Percentage of Sales (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2019	May 31, 2018	May 31, 2017
Business Segment Information
Net sales	$ 562.7	$ 529.5	$ 493.3	$ 466.3	$ 473.5	$ 456.3	$ 420.6	$ 397.9	$ 2,051.8	$ 1,748.3	$ 1,590.8
U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales									$ 546.2	$ 304.3	$ 321.5
Percentage of total sales									26.60%	17.40%	20.20%
Aviation Services
Business Segment Information
Net sales									$ 1,920.6	$ 1,635.8	$ 1,485.4
Aviation Services | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales									455.9	241.3	260.2
Expeditionary Services
Business Segment Information
Net sales									131.2	112.5	105.4
Expeditionary Services | U.S. Department of Defense, other U.S. government agencies and their contractors
Business Segment Information
Net sales									$ 90.3	$ 63.0	$ 61.3