Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended															12 Months Ended
	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015		Aug. 31, 2015		May 31, 2015		Feb. 28, 2015		Nov. 30, 2014		Aug. 31, 2014		Nov. 30, 2013	May 31, 2016	May 31, 2015	May 31, 2014
Segment Reporting Information [Line Items]
Net sales	$ 714,671	$ 647,080	$ 699,816		$ 758,147		$ 846,023		$ 804,785		$ 871,012		$ 862,414			$ 2,819,714	$ 3,384,234	$ 3,126,426
Operating income (loss)																122,052	60,557	135,753
Depreciation and amortization																84,699	85,089	79,730
Impairment of goodwill and long-lived assets			$ 22,962	[1]	3,000	[1]	2,344	[1]	$ 81,600	[1]	14,235	[1]	$ 1,950	[1]	$ 30,734	25,962	100,129	58,246
Restructuring and other expense (income)																7,177	6,927	(1,876)
Total assets	2,063,755						2,085,142									2,063,755	2,085,142	2,296,381
Total capital expenditures																97,036	96,255	71,338
Steel Processing
Segment Reporting Information [Line Items]
Net sales																1,843,661	2,145,744	1,936,073
Operating income (loss)																112,001	108,707	119,025
Depreciation and amortization																38,523	34,526	32,882
Impairment of goodwill and long-lived assets																	3,050	7,141
Restructuring and other expense (income)																4,110	72	(3,382)
Total assets	819,853						829,116									819,853	829,116	850,748
Total capital expenditures																42,063	34,546	16,682
Pressure Cylinders
Segment Reporting Information [Line Items]
Net sales																844,898	1,001,402	928,396
Operating income (loss)																28,375	58,113	55,004
Depreciation and amortization																32,403	34,953	31,984
Impairment of goodwill and long-lived assets																22,962	11,911	32,005
Restructuring and other expense (income)																392	6,408	(745)
Total assets	787,786						804,799									787,786	804,799	818,720
Total capital expenditures																29,916	35,872	32,364
Engineered Cabs
Segment Reporting Information [Line Items]
Net sales																121,946	192,953	200,528
Operating income (loss)																(19,331)	(97,260)	(26,516)
Depreciation and amortization																6,205	10,184	10,027
Impairment of goodwill and long-lived assets					$ 3,000						$ 2,389					3,000	83,989	19,100
Restructuring and other expense (income)																3,570	(332)
Total assets	75,124						94,506									75,124	94,506	181,251
Total capital expenditures																6,945	8,951	10,351
Other
Segment Reporting Information [Line Items]
Net sales																9,209	44,135	61,429
Operating income (loss)																1,007	(9,003)	(11,760)
Depreciation and amortization																7,568	5,426	4,837
Impairment of goodwill and long-lived assets																	1,179
Restructuring and other expense (income)																(895)	779	2,251
Total assets	$ 380,992						$ 356,721									380,992	356,721	445,662
Total capital expenditures																$ 18,112	$ 16,886	$ 11,941

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