Revenue Recognition -Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Net sales	$ 3,050,376	$ 2,904,245	$ 2,874,473
Stormwater
Disaggregation of Revenue [Line Items]
Net sales	2,397,414	2,326,370	2,361,520
Stormwater \| Domestic Pipe
Disaggregation of Revenue [Line Items]
Net sales	1,495,555	1,521,939	1,556,575
Stormwater \| Domestic Allied Products
Disaggregation of Revenue [Line Items]
Net sales	750,498	645,448	627,825
Stormwater \| International
Disaggregation of Revenue [Line Items]
Net sales	187,827	194,630	207,769
Wastewater
Disaggregation of Revenue [Line Items]
Net sales	652,962	577,875	512,953
Operating Segments \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	2,433,880	2,362,017	2,392,169
Operating Segments \| Wastewater
Disaggregation of Revenue [Line Items]
Net sales	714,542	629,906	566,550
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Net sales	(98,046)	(87,678)	(84,246)
Intersegment Eliminations \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	36,466	35,647	30,649
Intersegment Eliminations \| Wastewater
Disaggregation of Revenue [Line Items]
Net sales	$ 61,580	$ 52,031	$ 53,597

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details