CONSOLIDATED STATEMENTS OF COMPREHENSIVE (LOSS) INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Feb. 23, 2020	Feb. 28, 2021	Feb. 23, 2020
Income Statement [Abstract]
Product sales	$ 137,782	$ 152,928	$ 404,328	$ 434,235
Cost of product sales	118,093	132,881	347,657	383,338
Gross profit	19,689	20,047	56,671	50,897
Operating costs and expenses:
Research and development	2,562	2,747	7,643	8,390
Selling, general and administrative	15,220	18,783	49,227	54,000
Legal settlement charge	0	0	1,763	0
Restructuring costs	2,700	13,528	12,766	13,934
Total operating costs and expenses	20,482	35,058	71,399	76,324
Operating loss	(793)	(15,011)	(14,728)	(25,427)
Dividend income	281	281	844	843
Interest income	13	46	31	96
Interest expense, net	(4,178)	(2,211)	(10,326)	(6,455)
Loss on debt refinancing	(1,110)	0	(1,110)	0
Other income (expense), net	72	67	(11,736)	61
Net loss before tax	(5,715)	(16,828)	(37,025)	(30,882)
Income tax benefit	217	5,310	7,226	7,840
Net loss	$ (5,498)	$ (11,518)	$ (29,799)	$ (23,042)
Net loss per common share:
Net loss per common share - basic (in dollars per share)	$ (0.19)	$ (0.39)	$ (1.02)	$ (0.79)
Net loss per common share - diluted (in dollars per share)	$ (0.19)	$ (0.39)	$ (1.02)	$ (0.79)
Net loss per common share:
Basic (in shares)	29,323	29,170	29,282	29,155
Diluted (in shares)	29,323	29,170	29,282	29,155
Other comprehensive income (loss), net of tax:
Net unrealized gain (loss) on interest rate swaps (net of tax effect of $(99), $124, $(327), and $305)	$ 387	$ (411)	$ 1,092	$ (896)
Other comprehensive income (loss), net of tax	387	(411)	1,092	(896)
Total comprehensive loss	$ (5,111)	$ (11,929)	$ (28,707)	$ (23,938)