Fair Value Measurements (Tables)

9 Months Ended

Feb. 28, 2013

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 February 28, 2013
	Level 1		Level 2		Level 3		Fair Value
Cash and cash equivalents	$	217,470	$	—	$	—	$	217,470
Marketable securities:
U.S. municipal bonds	—		5,812		—		5,812
Canadian treasury securities	—		22,404		—		22,404
Total assets at fair value	$	217,470	$	28,216	$	—	$	245,686

(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