Warranty (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012
Summary of accrued warranty and related expenses
Balance at the beginning of the period	$ 5,870	$ 4,966
Accruals for warranties	5,191	5,990
Settlements made during the period	(5,179)	(5,086)
Balance at the end of the period	5,882	5,870
Non-current balance included in other deferred liabilities	2,200	2,000
Accrued warranty and related expenses	$ 3,682	$ 3,870