Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities.

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Financing Arrangements (Details) - USD ($) $ in Millions	3 Months Ended
Financing Arrangements (Details) - USD ($) $ in Millions	Aug. 31, 2016	Aug. 31, 2015	May 31, 2016
Financing Arrangements
Total debt	$ 151.6		$ 150.1
Current maturities of debt	(7.0)		(12.0)
Debt issuance costs, net	(1.8)		(2.0)
Long-term debt	142.8		136.1
Loss on extinguishment of debt		$ 0.3
Capital lease obligations
Financing Arrangements
Total debt	4.6		5.1
Revolving Credit Facility expiring March 24, 2020 with interest payable monthly
Financing Arrangements
Total debt	117.0		110.0
Industrial revenue bond (secured by property, plant and equipment) due August 1, 2018 with interest payable monthly
Financing Arrangements
Total debt	25.0		25.0
Note payable due March 9, 2017 with floating interest rate, payable semi-annually on June 1 and December 1
Financing Arrangements
Total debt	5.0		$ 10.0
Convertible notes payable
Financing Arrangements
Interest expense related to convertible notes	$ 0.0	0.9
Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1
Financing Arrangements
Amount of convertible notes repurchased		$ 14.4
Interest rate (as a percent)		2.25%
Cash paid for convertible notes repurchased		$ 14.6
Accrued interest		0.2
Loss on extinguishment of debt		$ 0.3