CREDIT ARRANGEMENTS (Long-term Debt) (Details) - USD ($) $ in Thousands	Aug. 31, 2020	May 31, 2020	Aug. 31, 2019	Jul. 31, 2017	May 31, 2013
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 1,092,266		$ 1,254,921
Less debt issuance costs	8,581		10,268
Total amounts outstanding	1,083,685		1,244,653
Current maturities of long-term debt and short-term borrowings	18,149		17,439
Long-term debt	$ 1,065,536		1,227,214
2027 Notes
Debt Instrument [Line Items]
Weighted average interest rate	5.375%			5.375%
Total long-term debt including current maturities	$ 300,000		300,000
2026 Notes
Debt Instrument [Line Items]
Weighted average interest rate	5.75%	5.75%
Total long-term debt including current maturities	$ 350,000		350,000
2023 Notes
Debt Instrument [Line Items]
Weighted average interest rate	4.875%				4.875%
Total long-term debt including current maturities	$ 330,000		330,000
Other
Debt Instrument [Line Items]
Weighted average interest rate	5.10%
Total long-term debt including current maturities	$ 21,329		23,168
Short-term borrowings
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 0		3,929
Short-term borrowings | Poland Program
Debt Instrument [Line Items]
Weighted average interest rate	0.98%
Finance leases
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 50,224		37,699
Revolving credit agreement | Poland Term Loan
Debt Instrument [Line Items]
Weighted average interest rate	1.73%
Total long-term debt including current maturities	$ 40,713		0
Revolving credit agreement | Term Loan
Debt Instrument [Line Items]
Weighted average interest rate	3.148%
Total long-term debt including current maturities	$ 0		$ 210,125