Operating segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Nov. 30, 2023	Nov. 30, 2022	Nov. 30, 2023	Nov. 30, 2022	Feb. 28, 2023	Sep. 30, 2022
Operations and assets by segment
Sales	$ 381,605	$ 373,301	$ 1,171,020	$ 987,145
Cost of sales	293,456	300,219	888,606	752,455
Gross margin	88,149	73,082	282,414	234,690
Selling, general and administrative	35,325	27,689	103,087	97,247
Operating income (loss)	52,824	45,393	179,327	137,443
Interest expense	25,855	26,123	82,331	61,739
Equity in (earnings) loss of unconsolidated subsidiaries	(8,742)	(1,006)	(11,136)	(1,006)
Other expense	41	(610)	(9)	(582)
Income taxes	8,780	2,447	24,397	18,380
Net income from continuing operations	26,890	18,439	83,744	58,912
Income (loss) from continuing operations before income tax	35,670	20,886	108,141	77,292
Assets:	2,208,756		2,208,756		$ 2,221,479
Property, plant and equipment, net	525,338		525,338		498,503
AIS Joint Venture
Operations and assets by segment
Ownership percentage of investment						40.00%
United States
Operations and assets by segment
Sales	370,485	363,660	1,140,344	951,855
Property, plant and equipment, net	506,070		506,070		478,722
Canada
Operations and assets by segment
Sales	11,120	9,641	30,676	35,290
Property, plant and equipment, net	19,268		19,268		19,781
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	17,480	9,206	52,271	50,283
Operating income (loss)	(17,480)	(9,206)	(52,271)	(50,283)
Interest expense	25,855	26,123	82,331	61,739
Equity in (earnings) loss of unconsolidated subsidiaries	0	0	0	0
Other expense	12	(486)	(49)	(547)
Income taxes	8,780	2,447	24,397	18,380
Net income from continuing operations	(52,127)	(37,290)	(158,950)	(129,855)
Income (loss) from continuing operations before income tax	(43,347)	(34,843)	(134,553)	(111,475)
Assets:	47,541		47,541		59,572
Metal Coatings | Operating Segments
Operations and assets by segment
Sales	163,186	158,274	501,816	487,567
Cost of sales	115,952	120,134	353,280	350,152
Gross margin	47,234	38,140	148,536	137,415
Selling, general and administrative	9,392	4,594	20,143	13,603
Operating income (loss)	37,842	33,546	128,393	123,812
Interest expense	0	0	0	0
Equity in (earnings) loss of unconsolidated subsidiaries	0	0	0	0
Other expense	29	(124)	40	6
Income (loss) from continuing operations before income tax	37,813	33,670	128,353	123,806
Assets:	559,149		559,149		588,337
Precoat Metals | Operating Segments
Operations and assets by segment
Sales	218,419	215,027	669,204	499,578
Cost of sales	177,504	180,085	535,326	402,303
Gross margin	40,915	34,942	133,878	97,275
Selling, general and administrative	8,163	13,889	24,429	33,361
Operating income (loss)	32,752	21,053	109,449	63,914
Interest expense	0	0	0	0
Equity in (earnings) loss of unconsolidated subsidiaries	0	0	0	0
Other expense	0	0	0	(41)
Income (loss) from continuing operations before income tax	32,752	21,053	109,449	63,955
Assets:	1,504,828		1,504,828		1,488,810
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	290	0	6,244	0
Operating income (loss)	(290)	0	(6,244)	0
Interest expense	0	0	0	0
Equity in (earnings) loss of unconsolidated subsidiaries	(8,742)	(1,006)	(11,136)	(1,006)
Other expense	0	0	0	0
Income (loss) from continuing operations before income tax	8,452	$ 1,006	4,892	$ 1,006
Assets:	$ 97,238		$ 97,238		$ 84,760