Segment Operations - Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019	May 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 763,996	$ 874,381	$ 2,447,492	$ 2,820,714
Operating income (loss)	(1,386)	25,977	16,144	112,752
Impairment of goodwill and long-lived assets	34,627	0	75,228	2,381
Restructuring and other expense (income), net	1,376	(11,176)	1,781	(11,710)
Total assets	2,429,083		2,429,083		$ 2,510,796
Steel Processing
Segment Reporting Information [Line Items]
Net sales	491,136	555,871	1,531,448	1,851,401
Operating income (loss)	19,021	10,166	42,361	74,842
Impairment of goodwill and long-lived assets	1,274	0	1,274	0
Restructuring and other expense (income), net	728	0	702	(9)
Total assets	921,969		921,969		924,966
Pressure Cylinders
Segment Reporting Information [Line Items]
Net sales	270,995	290,690	865,527	885,490
Operating income (loss)	(19,865)	18,953	25,405	48,444
Impairment of goodwill and long-lived assets	33,353	0	33,353	2,381
Restructuring and other expense (income), net	747	(11,176)	747	(11,701)
Total assets	1,078,167		1,078,167		1,123,115
Other
Segment Reporting Information [Line Items]
Net sales	1,865	27,820	50,517	83,823
Operating income (loss)	(542)	(3,142)	(51,622)	(10,534)
Impairment of goodwill and long-lived assets	0	0	40,601	0
Restructuring and other expense (income), net	(99)	$ 0	332	$ 0
Total assets	$ 428,947		$ 428,947		$ 462,715