Consolidated Statement of Shareholders' Equity and Comprehensive Income (USD $) In Thousands	Total USD ($)		Common Stock Shares [Member]	Common Stock Amount [Member] USD ($)	Additional Paid-in Capital [Member] USD ($)	Retained Earnings [Member] USD ($)	Accumulated Other Comprehensive Income (Loss) [Member] USD ($)		Total Shareholders Equity [Member] USD ($)
Balance at May. 31, 2008				$ 7,014	$ 37,325	$ 251,059	$ 12,298	[1]	$ 307,696
Balance (in Shares) at May. 31, 2008			70,136
Shares issued under employee stock plan				67	3,632				3,699
Shares issued under employee stock plan (in Shares)			669
Share-based compensation expense	5,904				5,904				5,904
Stock repurchases and retirements				(35)	(8,102)				(8,137)
Stock repurchases and retirements (in Shares)			(349)
Tax benefits related to stock-based compensation					3,253				3,253
Comprehensive income (net of taxes):
Foreign currency translation adjustments							(4,020)	[1]	(4,020)
Net income	76,183	[2]				76,183			76,183
Total comprehensive income									72,163
Balance at May. 31, 2009				7,046	42,012	327,242	8,278	[1]	384,578
Balance (in Shares) at May. 31, 2009			70,456
Shares issued under employee stock plan				12	324				336
Shares issued under employee stock plan (in Shares)			125
Share-based compensation expense	5,946				5,946				5,946
Stock repurchases and retirements				(67)	(11,843)				(11,910)
Stock repurchases and retirements (in Shares)			(669)
Tax benefits related to stock-based compensation					(183)				(183)
Comprehensive income (net of taxes):
Foreign currency translation adjustments							(5,227)	[1]	(5,227)
Net income	82,583					82,583			82,583
Total comprehensive income									77,356
Balance at May. 31, 2010	456,123			6,991	36,256	409,825	3,051	[1]	456,123
Balance (in Shares) at May. 31, 2010			69,912
Shares issued under employee stock plan				48	1,264				1,312
Shares issued under employee stock plan (in Shares)			482
Share-based compensation expense	6,941				6,941				6,941
Stock repurchases and retirements				(2)	(524)				(526)
Stock repurchases and retirements (in Shares)			(27)
Tax benefits related to stock-based compensation					1,792				1,792
Comprehensive income (net of taxes):
Foreign currency translation adjustments							13,903	[1]	13,903
Net income	89,327					89,327			89,327
Total comprehensive income									103,230
Balance at May. 31, 2011	$ 568,872			$ 7,037	$ 45,729	$ 499,152	$ 16,954	[1]	$ 568,872
Balance (in Shares) at May. 31, 2011			70,367

[1] Accumulated Other Comprehensive Income balance primarily consists of foreign currency translation adjustments and has no tax effect.

[2] Certain numbers have been reclassed to conform to current year presentation.