Revenue Recognition - Schedule of Contract Asset and Liability (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Mar. 31, 2026
Disaggregation of Revenue [Line Items]
Net sales	$ 889,406	$ 850,381	$ 1,890,518	$ 1,680,261
Contract asset - product returns	2,120		2,120		$ 1,383
Refund liability	6,736		6,736		$ 4,112
Stormwater
Disaggregation of Revenue [Line Items]
Net sales	712,063	670,665	1,521,439	1,322,192
Wastewater
Disaggregation of Revenue [Line Items]
Net sales	177,343	179,716	369,079	358,069
Domestic Pipe \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	390,309	422,384	848,397	846,990
Domestic Allied Products \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	276,511	198,970	579,898	386,476
International \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	56,277	58,657	115,744	107,148
Operating Segments \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	723,097	680,011	1,544,039	1,340,614
Operating Segments \| Wastewater
Disaggregation of Revenue [Line Items]
Net sales	197,575	196,368	406,495	391,330
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Net sales	(31,266)	(25,998)	(60,016)	(51,683)
Intersegment Eliminations \| Stormwater
Disaggregation of Revenue [Line Items]
Net sales	11,034	9,346	22,600	18,422
Intersegment Eliminations \| Wastewater
Disaggregation of Revenue [Line Items]
Net sales	$ 20,232	$ 16,652	$ 37,416	$ 33,261