Segment Data - Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended													12 Months Ended
	May 31, 2020		Feb. 29, 2020		Nov. 30, 2019	Aug. 31, 2019		May 31, 2019		Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018		May 31, 2020	May 31, 2019	May 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 611,627		$ 763,996		$ 827,637	$ 855,859		$ 938,842		$ 874,381	$ 958,226	$ 988,107		$ 3,059,119	$ 3,759,556	$ 3,581,620
Operating income (loss)														22,489	144,764	141,610
Depreciation and amortization														92,678	95,602	103,359
Impairment of goodwill and long-lived assets	7,462	[1]	$ 34,627	[1]		$ 40,601	[1]	5,436	[1]			$ 2,381	[1]	82,690	7,817	61,208
Restructuring and other expense (income), net														10,048	(11,018)	(7,421)
Total assets	2,331,515							2,510,796						2,331,515	2,510,796	2,621,787
Total capital expenditures														95,503	84,499	76,088
Steel Processing
Segment Reporting Information [Line Items]
Net sales														1,859,670	2,435,818	2,252,771
Operating income (loss)														40,564	89,761	152,690
Depreciation and amortization														40,819	40,374	43,331
Impairment of goodwill and long-lived assets														1,839	3,269
Restructuring and other expense (income), net														3,501	(9)	(10,087)
Total assets	821,657							924,966						821,657	924,966	999,238
Total capital expenditures														40,588	39,114	31,966
Pressure Cylinders
Segment Reporting Information [Line Items]
Net sales														1,148,424	1,207,798	1,206,183
Operating income (loss)														38,903	69,872	23,396
Depreciation and amortization														42,565	42,403	46,691
Impairment of goodwill and long-lived assets														37,153	4,548	53,883
Restructuring and other expense (income), net														5,282	(11,009)	2,365
Total assets	1,104,603							1,123,115						1,104,603	1,123,115	1,147,268
Total capital expenditures														41,484	37,558	32,697
Other
Segment Reporting Information [Line Items]
Net sales														51,025	115,940	122,666
Operating income (loss)														(56,978)	(14,869)	(34,476)
Depreciation and amortization														9,294	12,825	13,337
Impairment of goodwill and long-lived assets														43,698		7,325
Restructuring and other expense (income), net														1,265		301
Total assets	$ 405,255							$ 462,715						405,255	462,715	475,281
Total capital expenditures														$ 13,431	$ 7,827	$ 11,425

[1] For additional information regarding the Company’s impairment activity, refer to “Note D – Goodwill and Other Long-Lived Assets.”