Stock-Based Compensation (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	May 31, 2013
Options Outstanding
Number Outstanding at the end of the period (in shares)	2,300
Weighted-Average Remaining Contractual Life in Years	7 years 4 months 24 days
Weighted-Average Exercise Price (in dollars per Share)	$ 16.22
Options Exercisable
Number Outstanding at the end of the period (in shares)	1,089
Weighted-Average Exercise Price (in dollar per Share)	$ 17.73
$6.50 - $15.00
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 6.50
Option Exercise Price Range, high end of range (in dollars per share)	$ 15.00
Options Outstanding
Number Outstanding at the end of the period (in shares)	937
Weighted-Average Remaining Contractual Life in Years	8 years 9 months 18 days
Weighted-Average Exercise Price (in dollars per Share)	$ 12.74
Options Exercisable
Number Outstanding at the end of the period (in shares)	40
Weighted-Average Exercise Price (in dollar per Share)	$ 9.09
$15.01 - $20.00
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 15.01
Option Exercise Price Range, high end of range (in dollars per share)	$ 20.00
Options Outstanding
Number Outstanding at the end of the period (in shares)	1,138
Weighted-Average Remaining Contractual Life in Years	6 years 6 months
Weighted-Average Exercise Price (in dollars per Share)	$ 16.49
Options Exercisable
Number Outstanding at the end of the period (in shares)	903
Weighted-Average Exercise Price (in dollar per Share)	$ 16.25
$20.01 - $34.50
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 20.01
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)	225
Weighted-Average Remaining Contractual Life in Years	6 years 6 months
Weighted-Average Exercise Price (in dollars per Share)	$ 29.33
Options Exercisable
Number Outstanding at the end of the period (in shares)	146
Weighted-Average Exercise Price (in dollar per Share)	$ 29.29