Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2020	Aug. 31, 2019
Disaggregation of revenue by major customer markets
Net sales	$ 400.8	$ 541.5
Aviation Services
Disaggregation of revenue by major customer markets
Net sales	363.6	511.8
Aviation Services | North America
Disaggregation of revenue by major customer markets
Net sales	294.8	390.4
Aviation Services | Europe
Disaggregation of revenue by major customer markets
Net sales	51.0	88.2
Aviation Services | Other
Disaggregation of revenue by major customer markets
Net sales	17.8	33.2
Aviation Services | Commercial
Disaggregation of revenue by major customer markets
Net sales	169.6	330.5
Aviation Services | Government and defense
Disaggregation of revenue by major customer markets
Net sales	194.0	181.3
Expeditionary Services
Disaggregation of revenue by major customer markets
Net sales	37.2	29.7
Expeditionary Services | North America
Disaggregation of revenue by major customer markets
Net sales	34.9	28.2
Expeditionary Services | Europe
Disaggregation of revenue by major customer markets
Net sales	2.2	1.4
Expeditionary Services | Other
Disaggregation of revenue by major customer markets
Net sales	0.1	0.1
Expeditionary Services | Commercial
Disaggregation of revenue by major customer markets
Net sales	5.7	5.7
Expeditionary Services | Government and defense
Disaggregation of revenue by major customer markets
Net sales	$ 31.5	$ 24.0