Equity - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
May 31, 2021	May 31, 2020	May 31, 2019
Restricted stock
Number of Shares
Nonvested at the beginning of the period ( in shares)	385,000
Granted (in shares)	290,000
Vested (in shares)	(292,000)
Forfeited (in shares)	(14,000)
Nonvested at the end of the period (in shares)	369,000	385,000
Weighted Average Fair Value on Grant Date
Nonvested at the beginning of the period (in dollars per share)	$ 31.70
Granted (in dollars per share)	23.43
Vested (in dollars per share)	32.15
Forfeited (in dollars per share)	26.60
Nonvested at the end of the period (in dollars per share)	$ 30.12	$ 31.70
Unearned compensation not yet recognized	$ 2.5
Average remaining expensed period of unearned compensation	2 years
Restricted stock \| Selling, general and administrative expenses
Restricted Stock
Compensation expense	$ 5.2	$ 3.4	$ 9.4
Performance Based Restricted Stock \| Executives and other key employees
Number of Shares
Granted (in shares)	0	52,475	43,680
Time Based Restricted Stock \| Board of Directors
Number of Shares
Granted (in shares)	72,021	44,123	29,128
Time Based Restricted Stock \| Executives and other key employees
Number of Shares
Granted (in shares)	144,255	56,535	46,470

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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