Business Segment Information - Major Customer Markets (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
Disaggregation of revenue by major customer markets
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
Aviation Services
Disaggregation of revenue by major customer markets
Sales									1,920.6	1,635.8	1,485.4
Aviation Services | Commercial
Disaggregation of revenue by major customer markets
Sales									1,342.3	1,281.9	1,114.9
Aviation Services | Government and defense
Disaggregation of revenue by major customer markets
Sales									578.3	353.9	370.5
Expeditionary Services
Disaggregation of revenue by major customer markets
Sales									131.2	112.5	105.4
Expeditionary Services | Commercial
Disaggregation of revenue by major customer markets
Sales									31.6	37.5	37.1
Expeditionary Services | Government and defense
Disaggregation of revenue by major customer markets
Sales									$ 99.6	$ 75.0	$ 68.3