Accounts Receivable (Details) - USD ($) $ in Millions	Feb. 29, 2020	May 31, 2019
Accounts receivable, net	$ 225.7	$ 197.8
Past due accounts receivable	9.9
Allowance for doubtful accounts	7.8
US Government Contract
Accounts receivable, net	70.9	60.4
Unbilled receivables	30.5	31.7
US Government Contract | Trade receivables
Accounts receivable, net	40.4	28.7
All other customers
Accounts receivable, net	154.8	137.4
Unbilled receivables	37.5	44.9
All other customers | Trade receivables
Accounts receivable, net	$ 117.3	$ 92.5