Summary of Significant Accounting Policies - Intangibles (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2017
Amortizable intangible assets:
Gross carrying amount	$ 51.4	$ 60.0
Accumulated Amortization	(30.3)	(33.3)
Net carrying amount	21.1	26.7
Unamortized intangible assets:
Trademarks	1.1	1.1
Intangible Assets, Gross (Excluding Goodwill)	52.5	61.1
Intangible Assets, Net (Excluding Goodwill), Total	22.2	27.8
Amortization expense	3.9	4.7	$ 4.2
Estimated aggregate amortization expense for intangible assets in each of the next five fiscal years
2020	3.7
2021	3.7
2022	2.8
2023	2.3
2024	2.1
Customer relationships
Amortizable intangible assets:
Gross carrying amount	25.5	26.3
Accumulated Amortization	(15.6)	(13.9)
Net carrying amount	9.9	12.4
Lease agreements
Amortizable intangible assets:
Gross carrying amount	22.5	22.5
Accumulated Amortization	(14.0)	(12.6)
Net carrying amount	8.5	9.9
Other
Amortizable intangible assets:
Gross carrying amount	3.4	11.2
Accumulated Amortization	(0.7)	(6.8)
Net carrying amount	$ 2.7	$ 4.4
Minimum | Customer relationships
Unamortized intangible assets:
Useful life	5 years
Minimum | Lease agreements
Unamortized intangible assets:
Useful life	5 years
Maximum | Customer relationships
Unamortized intangible assets:
Useful life	20 years
Maximum | Lease agreements
Unamortized intangible assets:
Useful life	18 years