Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended											12 Months Ended
	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015		Aug. 31, 2015		Nov. 30, 2014	May 31, 2017	May 31, 2016	May 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 845,343	$ 703,436	$ 727,780	$ 737,549	$ 714,671	$ 647,080	$ 699,816		$ 758,147			$ 3,014,108	$ 2,819,714	$ 3,384,234
Operating income (loss)												213,121	122,052	60,557
Depreciation and amortization												86,793	84,699	85,089
Impairment of goodwill and long-lived assets							$ 22,962	[1]	3,000	[1]			25,962	100,129
Restructuring and other expense (income)												6,411	7,177	6,927
Total assets	2,325,344				2,061,264							2,325,344	2,061,264	2,082,305
Total capital expenditures												68,386	97,036	96,255
Steel Processing
Segment Reporting Information [Line Items]
Net sales												2,074,869	1,843,661	2,145,744
Operating income (loss)												170,481	112,001	108,707
Depreciation and amortization												42,861	38,523	34,526
Impairment of goodwill and long-lived assets														3,050
Restructuring and other expense (income)												1,828	4,110	72
Total assets	882,863				819,853							882,863	819,853	829,116
Total capital expenditures												40,775	42,063	34,546
Pressure Cylinders
Segment Reporting Information [Line Items]
Net sales												829,846	844,898	1,001,402
Operating income (loss)												54,098	28,375	58,113
Depreciation and amortization												31,052	32,403	34,953
Impairment of goodwill and long-lived assets													22,962	11,911
Restructuring and other expense (income)												3,411	392	6,408
Total assets	766,611				787,786							766,611	787,786	804,799
Total capital expenditures												24,798	29,916	35,872
Engineered Cabs
Segment Reporting Information [Line Items]
Net sales												101,388	121,946	192,953
Operating income (loss)												(7,685)	(19,331)	(97,260)
Depreciation and amortization												5,197	6,205	10,184
Impairment of goodwill and long-lived assets									$ 3,000		$ 2,389		3,000	83,989
Restructuring and other expense (income)												1,219	3,570	(332)
Total assets	62,141				75,124							62,141	75,124	94,506
Total capital expenditures												755	6,945	8,951
Other
Segment Reporting Information [Line Items]
Net sales												8,005	9,209	44,135
Operating income (loss)												(3,773)	1,007	(9,003)
Depreciation and amortization												7,683	7,568	5,426
Impairment of goodwill and long-lived assets														1,179
Restructuring and other expense (income)												(47)	(895)	779
Total assets	$ 613,729				$ 378,501							613,729	378,501	353,884
Total capital expenditures												$ 2,058	$ 18,112	$ 16,886

[1] For additional information regarding the Company's impairment activity, refer to "Note C - Goodwill and Other Long-Lived Assets."