Fair Value Measurements (Tables)

6 Months Ended

Nov. 30, 2012

Fair Value Disclosures [Abstract]

Schedule of fair value of financial instruments measured on a recurring basis

These financial instruments measured at fair value on a recurring basis are summarized below: 

(In thousands)	As of November 30, 2012
	Level 1		Level 2		Level 3		Fair Value
Cash and cash equivalents	$	242,487	$	—	$	—	$	242,487
Marketable securities:
U.S. municipal bonds	—		9,781		—		9,781
Canadian treasury securities	—		24,081		—		24,081
Total assets at fair value	$	242,487	$	33,862	$	—	$	276,349

(In thousands)	As of May 31, 2012
	Level 1		Level 2		Level 3		Fair Value
Cash and cash equivalents	$	339,825	$	—	$	—	$	339,825
Total assets at fair value	$	339,825	$	—	$	—	$	339,825