Summary of Significant Accounting Policies - Treasury Stock (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2023	May 31, 2024	May 31, 2023	May 31, 2022	May 31, 2021
Treasury Stocks
Repurchase of shares		$ 5.1	$ 50.1	$ 42.4
Shares repurchased (in shares)				1,000,000.0
Restricted stock activity		10.2	8.9	$ 3.8
Re-issuance of treasury stock upon exercise of stock options, net of shares withheld to satisfy statutory tax obligations		$ 24.6	$ 19.5	$ 21.3
Federal statutory income tax rate (as a percent)		21.00%	21.00%	21.00%
Minimum
Treasury Stocks
Federal statutory income tax rate (as a percent)	5.00%
Treasury Stock
Treasury Stocks
Total increase (decrease) in treasury stock			$ (28.7)	$ 15.0	$ (20.3)
Repurchase of shares		$ 5.1	$ 50.1	42.4
Shares repurchased (in shares)		100,000	1.2
Restricted stock activity		$ 3.7	$ 2.2	8.1
Re-issuance of treasury stock upon exercise of stock options, net of shares withheld to satisfy statutory tax obligations		$ 21.7	$ 19.2	$ 19.3