Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended			9 Months Ended		12 Months Ended
	Feb. 28, 2021 USD ($)	Nov. 30, 2020 segment	May 31, 2020 USD ($)	May 31, 2021 USD ($)	May 31, 2020 USD ($)	Aug. 31, 2020 USD ($) segment	May 22, 2021 USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | segment		1				2
Number of reportable segments | segment		1				2
Retained earnings, cumulative-effect adjustment				$ 756,262,000		$ 649,863,000
Bank Overdrafts				46,000,000		20,000,000
Repayment of Advances with Scrap Metal				7,000,000	$ 7,000,000
Investment, Original Cost				6,000,000
Insurance settlements receivable and losses related to plant, equipment and inventory assets damaged by fire							$ 1,000,000
Asset impairment charges			$ 2,227,000		$ 4,321,000
Cash, FDIC Insured Amount				250,000
Prepaid Expenses and Other Current Assets
Significant Accounting Policies [Line Items]
Prepaid expense				31,000,000		23,000,000
Other Assets
Significant Accounting Policies [Line Items]
Insurance receivable				12,000,000		5,000,000
Environmental claims insurance receivable				7,000,000
Workers' Compensation insurance receivables				4,000,000		4,000,000
Proceeds from legal settlements	$ 7,600,000
Investment, Carrying Value				6,000,000		6,000,000
Maximum | Other Assets
Significant Accounting Policies [Line Items]
Environmental claims insurance receivable						$ 1,000,000
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment | Maximum
Significant Accounting Policies [Line Items]
Retained earnings, cumulative-effect adjustment				$ 1,000,000