Segments - Net Sales by Main Product Lines (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Revenue from external customers
Total net sales	$ 1,150,551	$ 812,856	$ 2,192,627	$ 1,615,429
Wallboard
Revenue from external customers
Total net sales	414,522	330,515	804,657	658,600
Ceilings
Revenue from external customers
Total net sales	140,866	112,126	278,937	226,769
Steel framing
Revenue from external customers
Total net sales	272,000	111,293	468,276	221,825
Complementary products
Revenue from external customers
Total net sales	$ 323,163	$ 258,922	$ 640,757	$ 508,235