Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	May 31, 2023	May 31, 2022
Deferred tax assets
Net operating loss carryforward	$ 40,460	$ 40,759
Stock-based compensation	4,263	4,617
Federal and state R&D tax credit carryforward	7,311	6,320
Inventories	724	853
Expenses incurred not currently deductible	6,986	1,914
Accrued liabilities	78	72
Gross deferred tax asset	59,822	54,535
Deferred tax liabilities
Depreciation and amortization	46,828	50,320
Gross deferred tax liability	46,828	50,320
Valuation allowance	(25,759)	(20,203)
Net deferred tax liability	$ (12,765)	$ (15,988)