Stock-Based Compensation (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	May 31, 2012 Y
Options Outstanding
Number Outstanding at the end of the period (in shares)	1,703
Weighted-Average Remaining Contractual Life in Years	6.5
Weighted-Average Exercise Price (in dollar per Share)	$ 17.96
Options Exercisable
Number Outstanding at the end of the period (in shares)	880
Weighted-Average Exercise Price (in dollar per Share)	$ 17.1
$3.50 $13.00
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 3.50
Option Exercise Price Range, high end of range (in dollars per share)	$ 13.00
Options Outstanding
Number Outstanding at the end of the period (in shares)	69
Weighted-Average Remaining Contractual Life in Years	1.3
Weighted-Average Exercise Price (in dollar per Share)	$ 7.27
Options Exercisable
Number Outstanding at the end of the period (in shares)	69
Weighted-Average Exercise Price (in dollar per Share)	$ 7.27
$13.01 $18.50
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 13.01
Option Exercise Price Range, high end of range (in dollars per share)	$ 18.50
Options Outstanding
Number Outstanding at the end of the period (in shares)	1,289
Weighted-Average Remaining Contractual Life in Years	6.7
Weighted-Average Exercise Price (in dollar per Share)	$ 16.25
Options Exercisable
Number Outstanding at the end of the period (in shares)	655
Weighted-Average Exercise Price (in dollar per Share)	$ 15.95
$18.51 $24.50
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 18.51
Option Exercise Price Range, high end of range (in dollars per share)	$ 24.50
Options Outstanding
Number Outstanding at the end of the period (in shares)	135
Weighted-Average Remaining Contractual Life in Years	5.2
Weighted-Average Exercise Price (in dollar per Share)	$ 20.62
Options Exercisable
Number Outstanding at the end of the period (in shares)	81
Weighted-Average Exercise Price (in dollar per Share)	$ 21.47
$24.51 $34.50
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 24.51
Option Exercise Price Range, high end of range (in dollars per share)	$ 34.50
Options Outstanding
Number Outstanding at the end of the period (in shares)	210
Weighted-Average Remaining Contractual Life in Years	8.1
Weighted-Average Exercise Price (in dollar per Share)	$ 30.24
Options Exercisable
Number Outstanding at the end of the period (in shares)	75
Weighted-Average Exercise Price (in dollar per Share)	$ 31.27