Warranty - Reconciliation of Accrued Warranty (Detail) - USD ($) $ in Thousands	6 Months Ended
	Nov. 30, 2016	Nov. 30, 2015	Nov. 30, 2016	May 31, 2016	Nov. 30, 2015
Guarantees [Abstract]
Balance at the beginning of the period	$ 7,317	$ 6,911
Accruals for warranties	3,842	3,439
Settlements made during the period	(3,280)	(3,332)
Balance at the end of the period	7,879	7,018
Accrued warranty	$ 7,879	$ 7,018	$ 7,879	$ 7,317	$ 7,018
Non-current balance			2,500	2,500	2,400
Accrued warranty			$ 5,379	$ 4,817	$ 4,618