Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 399,197	$ 395,755	$ 428,016	$ 427,365	$ 407,399	$ 384,080	$ 424,878	$ 428,962	$ 1,650,333	$ 1,645,319	$ 1,250,274
Gross profit	75,269	72,348	87,050	94,519	87,122	76,853	86,762	95,736	329,186	346,473	255,403
Income before income taxes	16,958	17,274	29,978	36,338	28,814	24,126	25,409	32,539	100,548	110,888	94,760
Net income	$ 13,013	$ 12,804	$ 22,163	$ 26,881	$ 22,024	$ 18,409	$ 18,488	$ 24,767	$ 74,861	$ 83,688	$ 63,141
Earnings per share
Basic (usd per share)	$ 0.77	$ 0.76	$ 1.31	$ 1.59	$ 1.31	$ 1.07	$ 1.05	$ 1.41	$ 4.43	$ 4.84	$ 3.80
Diluted (usd per share)	$ 0.77	$ 0.75	$ 1.31	$ 1.59	$ 1.30	$ 1.07	$ 1.05	$ 1.41	$ 4.42	$ 4.83	$ 3.77