Segments - Net Sales by Main Product Lines (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2021	Jul. 31, 2020
Revenue from external customers
Total net sales	$ 1,042,076	$ 802,573
Wallboard
Revenue from external customers
Total net sales	390,135	328,085
Ceilings
Revenue from external customers
Total net sales	138,071	114,643
Steel framing
Revenue from external customers
Total net sales	196,276	110,532
Complementary products
Revenue from external customers
Total net sales	$ 317,594	$ 249,313