NEW MARKETS TAX CREDIT TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2017	Feb. 29, 2016	Aug. 31, 2017	May 31, 2017
Income Tax Contingency [Line Items]
Capital Contribution Received Under New Markets Tax Program		$ 17.7
Payments for qualified construction, development and equipping activities			$ 21.0
Restricted cash	$ 0.7		0.7
Commonwealth
Income Tax Contingency [Line Items]
Loans and Leases Receivable, Gross	$ 35.3		$ 35.3
Loan Receivable, Stated Interest Rate	1.08%		1.08%
Investment Fund
Income Tax Contingency [Line Items]
Qualified Equity Investment Into Community Development Entities			$ 51.5
Qualified Equity Investment Loans | CMC Steel Oklahoma, LLC
Income Tax Contingency [Line Items]
Loans Payable	$ 50.7		50.7
Post Shop Project
Income Tax Contingency [Line Items]
Payments for qualified construction, development and equipping activities			0.8
Restricted cash	0.0		0.0
Spooler Project
Income Tax Contingency [Line Items]
Restricted cash	18.8		$ 18.8
Fund 219
Income Tax Contingency [Line Items]
Period at end of which Company may be entitled or obligated to repurchase interest in the fund			8 years
Fund 219 | Post Shop Project
Income Tax Contingency [Line Items]
Capital Contribution Received Under New Markets Tax Program	$ 2.8
Loans and Leases Receivable, Gross				$ 10.4
Loan Receivable, Stated Interest Rate	1.16%		1.16%
Qualified Equity Investment Into Community Development Entities			$ 12.8
Fund 219 | Post Shop Project | Qualified Equity Investment Loans | CMC Steel Oklahoma, LLC
Income Tax Contingency [Line Items]
Loans Payable	$ 12.6		12.6
Fund 222 | Qualified Equity Investment Loans
Income Tax Contingency [Line Items]
Loans Payable	2.1		2.1
Fund 222 | Post Shop Project
Income Tax Contingency [Line Items]
Capital Contribution Received Under New Markets Tax Program	2.2
Qualified Equity Investment Into Community Development Entities			2.2
Fund 222 | Post Shop Project | Qualified Equity Investment Loans | CMC Steel Oklahoma, LLC
Income Tax Contingency [Line Items]
Loans Payable	2.1		$ 2.1
Fund 249
Income Tax Contingency [Line Items]
Period at end of which Company may be entitled or obligated to repurchase interest in the fund			7 years
Fund 249 | Spooler Project
Income Tax Contingency [Line Items]
Capital Contribution Received Under New Markets Tax Program	6.7
Loans and Leases Receivable, Gross	$ 14.0		$ 14.0
Loan Receivable, Stated Interest Rate	1.39%		1.39%
Qualified Equity Investment Into Community Development Entities	$ 20.0
Fund 249 | Spooler Project | Qualified Equity Investment Loans | CMC Steel Oklahoma, LLC
Income Tax Contingency [Line Items]
Loans Payable	$ 19.4		$ 19.4