Warranty - Reconciliation of Accrued Warranty (Detail) - USD ($) $ in Thousands	9 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	May 31, 2016	Feb. 29, 2016
Guarantees [Abstract]
Balance at the beginning of the period	$ 7,317	$ 6,911
Accruals for warranties	6,078	5,087
Settlements made during the period	(5,209)	(4,843)
Balance at the end of the period	8,186	7,155
Accrued warranty	$ 8,186	$ 7,155	$ 8,186	$ 7,317	$ 7,155
Non-current balance			2,500	2,500	2,400
Accrued warranty			$ 5,686	$ 4,817	$ 4,755