Treasury Stock - Schedule of repurchase of common stock (Details) - USD ($) $ in Millions			12 Months Ended			50 Months Ended
	May 16, 2022	Jan. 19, 2022	May 31, 2022	May 31, 2021	May 31, 2020	May 31, 2022	Mar. 18, 2020	Mar. 21, 2018
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Increase in Authorized Amount			$ 100.0			$ 100.0
Amount of stock repurchased in period			33.4	$ 0.0	$ 35.5	66.1
Remaining authorized repurchase amount			$ 33.9			$ 33.9
Repurchase of Common Stock
Equity, Class of Treasury Stock [Line Items]
Shares of stock repurchased (in shares)	190,290
Treasury Stock, Discount, Percent	4.00%
Repurchase of Common Stock | Former Chief Executive Officer, Estate
Equity, Class of Treasury Stock [Line Items]
Amount of stock repurchased in period		$ 12.2
Shares of stock repurchased (in shares)		300,000
Treasury Stock, Discount, Percent		4.20%
Board Authorized 2018 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Increase in Authorized Amount								$ 50.0
Board Authorized 2020 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Increase in Authorized Amount							$ 50.0