Operating segments (Details) (USD $)	3 Months Ended								12 Months Ended
	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2014	May 31, 2014	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2013	May 31, 2013	Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2013
Operations and assets by segment
Net sales	$ 182,312,000	$ 224,833,000	$ 193,416,000	$ 216,126,000	$ 181,011,000	$ 197,755,000	$ 189,782,000	$ 183,175,000	$ 816,687,000	$ 751,723,000	$ 570,594,000
Segment Operating income									106,825,000	100,114,000	97,984,000
Gain (Loss) on Disposition of Property Plant Equipment									(2,525,000)	(8,039,000)	(8,303,000)
Other Nonoperating Income (Expense)									(2,659,000)	4,165,000	1,155,000
Interest expense									16,561,000	18,407,000	13,073,000
Total Operating Income									90,130,000	93,911,000	94,369,000
Depreciation and amortization									46,089,000	43,305,000	29,363,000
Expenditures for acquisitions, net of cash, and property, plant and equipment									40,895,000	319,174,000	161,981,000
Assets	936,914,000				953,253,000				936,914,000	953,253,000	694,205,000
Goodwill	279,074,000				278,556,000				279,074,000	278,556,000	171,886,000
Property, Plant and Equipment, Net	196,583,000				197,639,000				196,583,000	197,639,000	154,476,000
Galvanizing Services [Member]
Operations and assets by segment
Net sales									358,348,000	335,617,000	337,039,000
Segment Operating income									88,562,000	87,808,000	88,505,000
Depreciation and amortization									23,964,000	22,008,000	19,501,000
Expenditures for acquisitions, net of cash, and property, plant and equipment									26,928,000	33,282,000	81,604,000
Assets	378,823,000				378,358,000				378,823,000	378,358,000	370,142,000
Goodwill	95,538,000				94,731,000				95,538,000	94,731,000	96,735,000
Corporate, Non-Segment [Member]
Operations and assets by segment
Segment Operating income									(20,440,000)	(32,207,000)	(22,594,000)
Corporate [Member]
Operations and assets by segment
Depreciation and amortization									1,400,000	1,338,000	1,275,000
Expenditures for acquisitions, net of cash, and property, plant and equipment									3,320,000	1,378,000	864,000
Assets	34,844,000				32,086,000				34,844,000	32,086,000	62,989,000
Energy [Member]
Operations and assets by segment
Net sales									458,339,000	416,106,000	233,555,000
Segment Operating income									38,703,000	44,513,000	32,073,000
Depreciation and amortization									20,725,000	19,959,000	8,587,000
Expenditures for acquisitions, net of cash, and property, plant and equipment									10,647,000	284,514,000	79,513,000
Assets	523,247,000				542,809,000				523,247,000	542,809,000	261,074,000
Goodwill	183,536,000				183,825,000				183,536,000	183,825,000	75,151,000
UNITED STATES
Operations and assets by segment
Net sales									631,544,000	601,674,000	503,699,000
Property, Plant and Equipment, Net	173,712,000				171,727,000				173,712,000	171,727,000	127,410,000
International [Member]
Operations and assets by segment
Net sales									189,855,000	150,049,000	66,895,000
Geography Eliminations [Member]
Operations and assets by segment
Net sales									(4,712,000)	0	0
CANADA
Operations and assets by segment
Property, Plant and Equipment, Net	20,289,000				23,779,000				20,289,000	23,779,000	27,066,000
Other Countries [Member]
Operations and assets by segment
Property, Plant and Equipment, Net	$ 2,582,000				$ 2,133,000				$ 2,582,000	$ 2,133,000	$ 0