Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended				5 Months Ended	7 Months Ended	12 Months Ended
	May 31, 2018	Feb. 28, 2018	May 31, 2017	Feb. 29, 2016	May 31, 2018	Dec. 31, 2017	May 31, 2018	May 31, 2017	May 31, 2016
Current:
U.S. federal statutory income tax rate (as a percent)					21.00%	35.00%	29.20%	35.00%	35.00%
Income tax benefit for the re-measurement impact	$ 1.1	$ 13.0					$ 14.1
Federal							14.6	$ 9.3	$ 13.7
State							0.1	0.2	0.4
Foreign							1.7	3.1	3.8
Total current							16.4	12.6	17.9
Deferred							(12.9)	12.5	5.5
Provision for income tax (benefit)							3.5	25.1	23.4
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Provision for income tax (benefit) at the federal statutory rate							22.5	27.0	24.1
Deferred tax re-measurement from the Tax Reform Act							(14.1)
Excess tax benefits from stock-based compensation							(2.9)
State net operating losses							1.3	5.7	1.1
Change in valuation allowance for state deferred tax assets							(3.4)	(5.7)	(1.1)
Prior period adjustments									(1.3)
Effective settlement of prior tax position								(2.2)
Other							0.1	0.3	0.6
Provision for income tax (benefit)							3.5	25.1	23.4
Income tax expense in discontinued operations			$ (6.7)	$ 2.8			(24.0)	(8.8)	7.7
Income tax benefit from continued operations							3.5	25.1	23.4
Income before provision for income taxes							77.2	77.1	68.9
Deferred tax assets:
Inventory costs	15.9		21.3		$ 15.9		15.9	21.3
Impairments	2.1		5.6		2.1		2.1	5.6
Postretirement benefits	2.2		6.8		2.2		2.2	6.8
Employee benefits	9.7		12.3		9.7		9.7	12.3
State net operating losses	8.6		9.4		8.6		8.6	9.4
Other	3.2		3.4		3.2		3.2	3.4
Total deferred tax assets	41.7		58.8		41.7		41.7	58.8
Valuation allowance	(7.0)		(10.4)		(7.0)		(7.0)	(10.4)
Total deferred tax assets net of valuation allowance	34.7		48.4		34.7		34.7	48.4
Deferred tax liabilities:
Tangible and intangible assets	(50.2)		(85.5)		(50.2)		(50.2)	(85.5)
Other	(0.2)		(0.1)		(0.2)		(0.2)	(0.1)
Total deferred tax liabilities	(50.4)		(85.6)		(50.4)		(50.4)	(85.6)
Net deferred tax liabilities	(15.7)		(37.2)		(15.7)		(15.7)	(37.2)
Reconciliation of unrecognized tax benefits
Balance, beginning of year						$ 4.4	4.4	12.9	2.2
Additions for tax positions of prior years								0.4	10.7
Effective settlement of prior tax position								(8.9)
Balance, end of year	4.4		4.4		4.4		$ 4.4	4.4	12.9
Unrecognized tax benefit resulting from statute lapse								2.2
Minimum
Deferred tax liabilities:
Period for net operating losses carry forward (in years)							5 years
Maximum
Deferred tax liabilities:
Period for net operating losses carry forward (in years)							20 years
Accrued Liabilities
Deferred tax liabilities:
Income tax payable			$ 12.3					12.3
Other Current Assets
Deferred tax liabilities:
Income tax receivable	$ 1.0				$ 1.0		$ 1.0
Domestic
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Income before provision for income taxes							58.7	57.7	55.7
Foreign
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Income before provision for income taxes							$ 18.5	$ 19.4	$ 13.2
Corrections
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Income tax expense in discontinued operations				1.5
Income tax benefit from continued operations				(1.3)
Immaterial errors
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Accrued Income Taxes				$ 0.2