Fair Value Measurements (Tables)

6 Months Ended

Nov. 30, 2015

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: 

	As of November 30, 2015
(In thousands)	Level 1		Level 2		Level 3		Fair Value
Cash and cash equivalents	$	556,809	$	49,976	$	—	$	606,785
Marketable securities:
Canadian treasury securities	—		65,826		—		65,826
Total assets at fair value	$	556,809	$	115,802	$	—	$	672,611

	As of May 31, 2015
(In thousands)	Level 1		Level 2		Level 3		Fair Value
Cash and cash equivalents	$	417,073	$	—	$	—	$	417,073
Marketable securities:
Canadian treasury securities	—		16,081		—		16,081
Total assets at fair value	$	417,073	$	16,081	$	—	$	433,154