Business Segment Information - Geographic Data (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
Long-lived assets	640.3				564.7				640.3	564.7
United States
Business Segment Information
Long-lived assets	423.9				345.4				423.9	345.4
Europe/Africa
Business Segment Information
Long-lived assets	102.1				108.7				102.1	108.7
Other
Business Segment Information
Long-lived assets	$ 114.3				$ 110.6				114.3	110.6
Foreign countries
Business Segment Information
Net sales									$ 591.8	$ 661.8	$ 694.0
Foreign countries | Total sales | Geographic concentration
Business Segment Information
Percentage of total sales									28.60%	32.30%	39.70%
Aviation Services
Business Segment Information
Net sales									$ 1,964.2	$ 1,920.6	$ 1,635.8
Aviation Services | North America
Business Segment Information
Net sales									1,505.6	1,426.8	1,131.4
Aviation Services | Europe/Africa
Business Segment Information
Net sales									330.8	323.4	325.9
Aviation Services | Other
Business Segment Information
Net sales									127.8	170.4	178.5
Expeditionary Services
Business Segment Information
Net sales									107.8	131.2	112.5
Expeditionary Services | North America
Business Segment Information
Net sales									98.4	124.1	105.3
Expeditionary Services | Europe/Africa
Business Segment Information
Net sales									9.0	5.8	6.9
Expeditionary Services | Other
Business Segment Information
Net sales									$ 0.4	$ 1.3	$ 0.3