CREDIT ARRANGEMENTS (Narrative) (Details)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 29, 2016 USD ($)	May 31, 2017 USD ($)	May 31, 2016 USD ($)	May 31, 2017 USD ($)	May 31, 2016 USD ($)	Aug. 31, 2012 USD ($)	May 31, 2017 PLN	May 31, 2017 USD ($)	Aug. 31, 2016 USD ($)	Aug. 31, 2014 USD ($)	May 31, 2013 USD ($)	May 31, 2011	May 31, 2010	Aug. 31, 2008 USD ($)	Jul. 31, 2007 USD ($)
Debt Instrument [Line Items]
Gain (Loss) on Extinguishment of Debt		$ 0	$ (115,000)	$ 0	$ (11,480,000)
Net proceeds from termination of interest rate swaps						$ 52,700,000
Unamortized deferred gain on termination of interest rate swaps								$ 5,900,000	$ 11,600,000
Amortization of interest rate swaps termination gain		(1,900,000)	(1,900,000)	(5,698,000)	(5,698,000)
Interest capitalized		2,900,000	600,000	6,600,000	1,600,000
Interest paid		$ 8,300,000	9,100,000	41,400,000	50,000,000
CMCP
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity							PLN 175,000,000	47,000,000.0
Stand by letters of credit outstanding amount								1,500,000	1,500,000
Total borrowing				0
Total payments				$ 0
2023 Notes
Debt Instrument [Line Items]
Debt instrument, face amount											$ 330,000,000
Debt instrument, interest rate, stated percentage											4.875%
Debt instrument, maturity date				May 15, 2023
2018 Notes
Debt Instrument [Line Items]
Debt instrument, face amount														$ 500,000,000
Debt instrument, interest rate, stated percentage														7.35%
Debt instrument, maturity date				August 2018
Debt instrument, effective interest rate													6.40%
Debt repurchased as a result of cash tender offer	$ 100,200,000
Gain (Loss) on Extinguishment of Debt			6,100,000		6,000,000
2017 Notes
Debt Instrument [Line Items]
Debt instrument, face amount															$ 400,000,000
Debt instrument, interest rate, stated percentage															6.50%
Debt instrument, maturity date				July 2017
Debt instrument, effective interest rate												5.74%
Debt repurchased as a result of cash tender offer	$ 100,000,000
Gain (Loss) on Extinguishment of Debt			$ 5,400,000		$ 5,400,000
Revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity										$ 350,000,000
Revolving credit facility, maturity date				Jun. 26, 2019
Revolving credit facility, maximum borrowing capacity										500,000,000
Revolving credit facility, amount drawn								0	$ 0
Minimum interest coverage ratio				2.50
Maximum debt to capitalization ratio				0.60
Minimum liquidity required								$ 150,000,000
Actual interest coverage ratio							5.98	5.98
Actual debt to capitalization ratio							0.43	0.43
Stand-by letters of credit
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity										$ 50,000,000
Stand by letters of credit outstanding amount								$ 3,000,000