Stock-Based Compensation (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	May 31, 2014
Options Outstanding
Number Outstanding at the end of the period (in shares)	2,753
Weighted-Average Remaining Contractual Life in Years	7 years 7 months 6 days
Weighted-Average Exercise Price (in dollars per Share)	$ 19.59
Options Exercisable
Number Outstanding at the end of the period (in shares)	1,019
Weighted-Average Exercise Price (in dollar per Share)	$ 17.88
$9.00 - $15.00
Share-Based Compensation
Option Exercise Price Range, low end of range (in dollars per share)	$ 9.00
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)	800
Weighted-Average Remaining Contractual Life in Years	8 years
Weighted-Average Exercise Price (in dollars per Share)	$ 12.86
Options Exercisable
Number Outstanding at the end of the period (in shares)	125
Weighted-Average Exercise Price (in dollar per Share)	$ 12.63
$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)	748
Weighted-Average Remaining Contractual Life in Years	5 years 7 months 6 days
Weighted-Average Exercise Price (in dollars per Share)	$ 16.17
Options Exercisable
Number Outstanding at the end of the period (in shares)	730
Weighted-Average Exercise Price (in dollar per Share)	$ 16.16
$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)	1,205
Weighted-Average Remaining Contractual Life in Years	8 years 6 months
Weighted-Average Exercise Price (in dollars per Share)	$ 26.17
Options Exercisable
Number Outstanding at the end of the period (in shares)	164
Weighted-Average Exercise Price (in dollar per Share)	$ 29.49