Operating segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Aug. 31, 2024	Aug. 31, 2023	Aug. 31, 2024	Aug. 31, 2023	Feb. 29, 2024	Sep. 30, 2022
Operations and assets by segment
Sales	$ 409,007	$ 398,542	$ 822,215	$ 789,415
Cost of sales	305,493	301,296	616,031	595,150
Gross margin	103,514	97,246	206,184	194,265
Selling, general and administrative	35,868	36,239	68,789	67,762
Operating income (loss)	67,646	61,007	137,395	126,503
Interest expense, net	(21,909)	(27,770)	(44,683)	(56,476)
Equity in earnings of unconsolidated subsidiaries	1,478	974	5,302	2,394
Other (expense) income	417	88	621	50
Income (loss) before income tax	47,632	34,299	98,635	72,471
Income taxes	12,213	5,967	23,614	15,617
Net income from continuing operations	35,419	28,332	75,021	56,854
Assets:	2,240,330		2,240,330		$ 2,195,505
Property, plant and equipment, net	$ 569,732		$ 569,732		541,652
AIS Joint Venture
Operations and assets by segment
Ownership percentage of investment	40.00%		40.00%			40.00%
United States
Operations and assets by segment
Sales	$ 398,658	388,538	$ 801,709	769,860
Property, plant and equipment, net	550,761		550,761		522,693
Canada
Operations and assets by segment
Sales	10,349	10,004	20,506	19,555
Property, plant and equipment, net	18,971		18,971		18,959
Corporate
Operations and assets by segment
Sales	0	0	0	0
Cost of sales	0	0	0	0
Gross margin	0	0	0	0
Selling, general and administrative	22,563	17,148	40,811	34,791
Operating income (loss)	(22,563)	(17,148)	(40,811)	(34,791)
Interest expense, net	(21,909)	(27,770)	(44,683)	(56,476)
Equity in earnings of unconsolidated subsidiaries	0	0	0	0
Other (expense) income	424	75	572	61
Income (loss) before income tax	(44,048)	(44,843)	(84,922)	(91,206)
Income taxes	12,213	5,967	23,614	15,617
Net income from continuing operations	(56,261)	(50,810)	(108,536)	(106,823)
Assets:	34,273		34,273		43,709
Metal Coatings | Operating Segments
Operations and assets by segment
Sales	171,500	169,837	348,152	338,631
Cost of sales	118,193	119,471	240,929	237,328
Gross margin	53,307	50,366	107,223	101,303
Selling, general and administrative	5,619	5,285	11,602	10,751
Operating income (loss)	47,688	45,081	95,621	90,552
Interest expense, net	0	0	0	0
Equity in earnings of unconsolidated subsidiaries	0	0	0	0
Other (expense) income	(7)	13	49	(11)
Income (loss) before income tax	47,681	45,094	95,670	90,541
Assets:	550,394		550,394		553,505
Precoat Metals | Operating Segments
Operations and assets by segment
Sales	237,507	228,705	474,063	450,784
Cost of sales	187,300	181,825	375,102	357,822
Gross margin	50,207	46,880	98,961	92,962
Selling, general and administrative	7,677	7,874	16,338	16,266
Operating income (loss)	42,530	39,006	82,623	76,696
Interest expense, net	0	0	0	0
Equity in earnings of unconsolidated subsidiaries	0	0	0	0
Other (expense) income	0	0	0	0
Income (loss) before income tax	42,530	39,006	82,623	76,696
Assets:	1,557,895		1,557,895		1,500,122
Infrastructure Solutions | Operating Segments
Operations and assets by segment
Sales	0	0	0	0
Cost of sales	0	0	0	0
Gross margin	0	0	0	0
Selling, general and administrative	9	5,932	38	5,954
Operating income (loss)	(9)	(5,932)	(38)	(5,954)
Interest expense, net	0	0	0	0
Equity in earnings of unconsolidated subsidiaries	1,478	974	5,302	2,394
Other (expense) income	0	0	0	0
Income (loss) before income tax	1,469	$ (4,958)	5,264	$ (3,560)
Assets:	$ 97,768		$ 97,768		$ 98,169