Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings
Beginning Balance (shares) at Apr. 30, 2017		38,765,821
Beginning Balance at Apr. 30, 2017	$ 1,190,620	$ 40,074	$ 1,150,546
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	317,903		317,903
Dividends declared	(39,060)		(39,060)
Exercise of stock options (shares)		40,377
Exercise of stock options	1,377	$ 1,377
Repurchase of common stock (shares)		(1,997,800)
Repurchase of common stock	(215,434)	$ (57,186)	(158,248)
Stock-based compensation (shares)		65,924
Stock-based compensation	15,735	$ 15,735
Ending Balance (shares) at Apr. 30, 2018		36,874,322
Ending Balance at Apr. 30, 2018	1,271,141	$ 0	1,271,141
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	203,886		203,886
Dividends declared	(42,471)		(42,471)
Exercise of stock options (shares)		71,546
Exercise of stock options	2,290	$ 2,290
Repurchase of common stock (shares)		(352,592)
Repurchase of common stock	(35,247)		(35,247)
Stock-based compensation (shares)		71,245
Stock-based compensation	$ 13,310	$ 13,310
Ending Balance (shares) at Apr. 30, 2019	36,664,521	36,664,521
Ending Balance at Apr. 30, 2019	$ 1,408,769	$ 15,600	1,393,169
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	263,846
Dividends declared	(47,096)		(47,096)
Exercise of stock options (shares)		66,638
Exercise of stock options	2,958	$ 2,958
Stock-based compensation (shares)		75,166
Stock-based compensation	$ 14,728	$ 14,728
Ending Balance (shares) at Apr. 30, 2020	36,806,325	36,806,325
Ending Balance at Apr. 30, 2020	$ 1,643,205	$ 33,286	$ 1,609,919