Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Feb. 29, 2016	May 31, 2016	May 31, 2015	May 31, 2014
Current:
Federal		$ 9.8	$ 22.2	$ 11.4
State		0.4	0.4	0.4
Foreign		3.8	1.5	0.8
Total current		14.0	24.1	12.6
Deferred		4.8	(52.6)	19.0
Provision for income tax (benefit)		$ 18.8	$ (28.5)	$ 31.6
U.S. federal statutory income tax rate (as a percent)		35.00%	35.00%	35.00%
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		$ 20.8	$ (29.0)	$ 34.6
State income taxes, net of federal benefit and refunds		0.2	0.2	0.2
Federal adjustments		0.3	0.5	(2.0)
Prior period adjustments		(2.5)
Domestic Production Activities Deduction			(0.2)	(1.2)
Provision for income tax (benefit)		18.8	(28.5)	31.6
Income tax expense in discontinued operations	$ 2.8	12.3	74.7	0.5
Income tax expense in continued operations		18.8	(28.5)	31.6
Income (Loss) before provision for income tax (benefit)		59.3	(83.0)	98.8
Deferred Tax Assets, Net of Valuation Allowance
Inventory costs		16.9	35.4
Advanced billings		11.0	14.3
Postretirement benefits		12.0	10.4
Employee benefits		9.8	12.0
Tax credits and incentives		2.3
Other		5.8	3.9
Total deferred tax assets		66.4	89.4
Valuation allowance		(4.7)	(2.8)
Total deferred tax assets net of valuation allowance		61.7	86.6
Deferred tax liabilities:
Tangible and intangible assets		95.9	132.4
Other		(0.1)	(0.5)
Total deferred tax liabilities		(96.0)	(132.9)
Net deferred tax liabilities		(34.3)	(46.3)
Reconciliation of unrecognized tax benefits
Beginning balance		2.2	2.2
Additions for tax positions of prior years		10.7		2.2
End balance		$ 12.9	2.2	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		$ 1.1
Deposits, prepaids and other
Deferred tax liabilities:
Income tax receivable			2.1
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 (Loss) before provision for income tax (benefit)		46.1	(94.2)	81.9
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 (Loss) before provision for income tax (benefit)		13.2	11.2	$ 16.9
Precision Systems Manufacturing
Deferred Tax Assets, Net of Valuation Allowance
Impairment of PSM assets		$ 8.6	$ 13.4
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
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	2.7
Income tax expense in continued operations	$ 2.5