NEW MARKETS TAX CREDIT TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2017	Feb. 28, 2017	May 31, 2017
Fund 222 | Qualified Equity Investment Loans
Income Tax Contingency [Line Items]
Loans payable	$ 2.1		$ 2.1
Micro-Mill Project
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
Micro-Mill Project | Commonwealth
Income Tax Contingency [Line Items]
Loans receivable		$ 35.3
Loan receivable, interest rate		1.08%
Micro-Mill Project | Investment Fund
Income Tax Contingency [Line Items]
Qualified equity investment into community development entities			51.5
Micro-Mill Project | 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]
Restricted cash	13.3		13.3
Post Shop Project | Fund 219
Income Tax Contingency [Line Items]
Capital contribution received under new markets tax program	2.8
Loans receivable	$ 10.4		$ 10.4
Loan receivable, interest rate	1.16%		1.16%
Qualified equity investment into community development entities			$ 12.8
Post Shop Project | Fund 219 | Qualified Equity Investment Loans | CMC Steel Oklahoma, LLC
Income Tax Contingency [Line Items]
Loans payable	$ 12.6		12.6
Post Shop Project | Fund 222
Income Tax Contingency [Line Items]
Capital contribution received under new markets tax program	2.2
Qualified equity investment into community development entities			2.2
Post Shop Project | Fund 222 | Qualified Equity Investment Loans | CMC Steel Oklahoma, LLC
Income Tax Contingency [Line Items]
Loans payable	$ 2.1		$ 2.1