Segment Data - Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended													12 Months Ended
	May 31, 2021	Feb. 28, 2021	Nov. 30, 2020		Aug. 31, 2020		May 31, 2020		Feb. 29, 2020		Nov. 30, 2019	Aug. 31, 2019		May 31, 2021	May 31, 2020	May 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 978,319	$ 759,109	$ 731,092		$ 702,909		$ 611,627		$ 763,996		$ 827,637	$ 855,859		$ 3,171,429	$ 3,059,119	$ 3,759,556
Operating income (loss)														167,473	22,489	144,764
Segment operating income														216,425	24,499	144,080
Incremental expenses related to Nikola gains														(50,624)
Depreciation and amortization														87,654	92,678	95,602
Impairment of goodwill and long-lived assets			$ 3,815	[1]	$ 9,924	[1]	7,462	[1]	$ 34,627	[1]		$ 40,601	[1]	13,739	82,690	7,817
Restructuring and other expense (income), net														56,097	10,048	(11,018)
Total assets	3,373,245						2,331,515							3,373,245	2,331,515	2,510,796
Total capital expenditures														82,178	95,503	84,499
Steel Processing
Segment Reporting Information [Line Items]
Net sales														2,059,397	1,859,670	2,435,818
Operating income (loss)														208,648	40,564	89,761
Depreciation and amortization														40,870	40,819	40,374
Impairment of goodwill and long-lived assets															1,839	3,269
Restructuring and other expense (income), net														1,883	3,501	(9)
Total assets	1,267,559						821,657							1,267,559	821,657	924,966
Total capital expenditures														28,306	40,588	39,114
Pressure Cylinders
Segment Reporting Information [Line Items]
Net sales														1,110,973	1,148,424	1,207,798
Operating income (loss)														9,276	38,903	69,872
Depreciation and amortization														38,885	42,565	42,403
Impairment of goodwill and long-lived assets														13,739	37,153	4,548
Restructuring and other expense (income), net														54,155	5,282	(11,009)
Total assets	1,156,092						1,104,603							1,156,092	1,104,603	1,123,115
Total capital expenditures														45,520	41,484	37,558
Other
Segment Reporting Information [Line Items]
Net sales														1,059	51,025	115,940
Operating income (loss)														(1,499)	(54,968)	(15,553)
Depreciation and amortization														7,899	9,294	12,825
Impairment of goodwill and long-lived assets															43,698
Restructuring and other expense (income), net														59	1,265
Total assets	$ 949,594						$ 405,255							949,594	405,255	462,715
Total capital expenditures														8,352	13,431	7,827
Unallocated Corporate Other
Segment Reporting Information [Line Items]
Operating income (loss)														$ 1,672	$ (2,010)	$ 684

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