MARKETABLE SECURITIES - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended	3 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011	May 31, 2011	Dec. 31, 2011 Kemrock global depository receipts	Feb. 29, 2012 Maximum	Feb. 28, 2011 Maximum
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, current	$ 116,600,000		$ 116,600,000		$ 113,800,000
Available-for-sale securities, long-term					35,800,000
Purchase of global depository receipt, shares						693,072
Purchase of global depository receipt, value						7,200,000
Gross gains realized on sales of investments	300,000	4,700,000	4,100,000	10,600,000
Gross losses realized on sales of investments	100,000	1,500,000	4,800,000	3,500,000
Losses recognized for securities deemed to have other-than-temporary impairments			800,000	500,000			100,000	100,000
Available-for-Sale Securities, gross unrealized losses	$ 1,388,000		$ 1,388,000		$ 1,518,000
Investments with unrealized loss, percentage of fair values less than original cost							15.00%