Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings
Beginning Balance (shares) at Apr. 30, 2019		36,664,521,000
Beginning Balance at Apr. 30, 2019	$ 1,408,769	$ 15,600	$ 1,393,169
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	85,815		85,815
Dividends declared	(11,772)		(11,772)
Exercise of stock options (in shares)		50,931,000
Exercise of stock options	2,261	$ 2,261
Share-based compensation (shares)		67,182,000
Share-based compensation	4,141	$ 4,141
Ending Balance (shares) at Jul. 31, 2019		36,782,634,000
Ending Balance at Jul. 31, 2019	1,489,214	$ 22,002	1,467,212
Beginning Balance (shares) at Apr. 30, 2019		36,664,521,000
Beginning Balance at Apr. 30, 2019	1,408,769	$ 15,600	1,393,169
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	201,755
Ending Balance (shares) at Jan. 31, 2020		36,793,573,000
Ending Balance at Jan. 31, 2020	1,588,590	$ 28,985	1,559,605
Beginning Balance (shares) at Jul. 31, 2019		36,782,634,000
Beginning Balance at Jul. 31, 2019	1,489,214	$ 22,002	1,467,212
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	81,981		81,981
Dividends declared	(11,773)		(11,773)
Exercise of stock options (in shares)		1,030,000
Exercise of stock options	46	$ 46
Share-based compensation (shares)		7,984,000
Share-based compensation	2,380	$ 2,380
Ending Balance (shares) at Oct. 31, 2019		36,791,648,000
Ending Balance at Oct. 31, 2019	1,561,848	$ 24,428	1,537,420
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,959		33,959
Dividends declared	(11,774)		(11,774)
Exercise of stock options (in shares)		1,925,000
Exercise of stock options	85	$ 85
Share-based compensation (shares)		0
Share-based compensation	4,472	$ 4,472
Ending Balance (shares) at Jan. 31, 2020		36,793,573,000
Ending Balance at Jan. 31, 2020	1,588,590	$ 28,985	1,559,605
Beginning Balance (shares) at Apr. 30, 2020		36,806,325,000
Beginning Balance at Apr. 30, 2020	1,643,205	$ 33,286	1,609,919
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120,592		120,592
Dividends declared	(11,874)		(11,874)
Exercise of stock options (in shares)		4,748,000
Exercise of stock options	211	$ 211
Share-based compensation (shares)		95,700,000
Share-based compensation	(896)	$ (896)
Ending Balance (shares) at Jul. 31, 2020		36,906,773,000
Ending Balance at Jul. 31, 2020	1,751,238	$ 32,601	1,718,637
Beginning Balance (shares) at Apr. 30, 2020		36,806,325,000
Beginning Balance at Apr. 30, 2020	1,643,205	$ 33,286	1,609,919
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	271,202
Ending Balance (shares) at Jan. 31, 2021		36,947,180,000
Ending Balance at Jan. 31, 2021	1,893,589	$ 48,855	1,844,734
Beginning Balance (shares) at Jul. 31, 2020		36,906,773,000
Beginning Balance at Jul. 31, 2020	1,751,238	$ 32,601	1,718,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	111,983		111,983
Dividends declared	(11,883)		(11,883)
Exercise of stock options (in shares)		23,470,000
Exercise of stock options	1,042	$ 1,042
Share-based compensation (shares)		5,504,000
Share-based compensation	7,471	$ 7,471
Ending Balance (shares) at Oct. 31, 2020		36,935,747,000
Ending Balance at Oct. 31, 2020	1,859,851	$ 41,114	1,818,737
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,627		38,627
Dividends declared	(12,630)		(12,630)
Exercise of stock options (in shares)		9,273,000
Exercise of stock options	412	$ 412
Share-based compensation (shares)		2,160,000
Share-based compensation	7,329	$ 7,329
Ending Balance (shares) at Jan. 31, 2021		36,947,180,000
Ending Balance at Jan. 31, 2021	$ 1,893,589	$ 48,855	$ 1,844,734