Accounts Receivable (Details) - USD ($) $ in Millions	Aug. 31, 2020	May 31, 2020
Accounts Receivable
Accounts receivable, net	$ 166.7	$ 171.9
Past due accounts receivable	10.5
Allowance for doubtful accounts	10.4
U.S. Government Contract
Accounts Receivable
Accounts receivable, net	69.5	61.3
Unbilled receivables	33.4	27.4
U.S. Government Contract | Trade receivables
Accounts Receivable
Accounts receivable, net	36.1	33.9
All other customers
Accounts Receivable
Accounts receivable, net	97.2	110.6
Unbilled receivables	19.5	28.9
All other customers | Trade receivables
Accounts Receivable
Accounts receivable, net	$ 77.7	$ 81.7