Condensed Consolidated Statements of Shareholders' Equity Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings
Beginning Balance (shares) at Apr. 30, 2018		36,874,322,000
Beginning Balance at Apr. 30, 2018	$ 1,271,141	$ 0	$ 1,271,141
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,224		70,224
Dividends declared	(10,601)		(10,601)
Exercise of stock options (in shares)		3,600,000
Exercise of stock options	148	$ 148
Repurchase of common stock (in shares)		(352,592,000)
Repurchase of common stock	(35,247)		(35,247)
Stock based compensation (shares)		67,895,000
Stock based compensation	7,174	$ 7,174
Ending Balance (shares) at Jul. 31, 2018		36,593,225,000
Ending Balance at Jul. 31, 2018	1,298,699	$ 7,322	1,291,377
Beginning Balance (shares) at Apr. 30, 2018		36,874,322,000
Beginning Balance at Apr. 30, 2018	1,271,141	$ 0	1,271,141
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	136,839
Ending Balance (shares) at Oct. 31, 2018		36,604,006,000
Ending Balance at Oct. 31, 2018	1,357,079	$ 9,702	1,347,377
Beginning Balance (shares) at Jul. 31, 2018		36,593,225,000
Beginning Balance at Jul. 31, 2018	1,298,699	$ 7,322	1,291,377
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	66,615		66,615
Dividends declared	(10,615)		(10,615)
Exercise of stock options (in shares)		7,692,000
Exercise of stock options	231	$ 231
Stock based compensation (shares)		3,089,000
Stock based compensation	2,149	$ 2,149
Ending Balance (shares) at Oct. 31, 2018		36,604,006,000
Ending Balance at Oct. 31, 2018	1,357,079	$ 9,702	1,347,377
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
Stock based compensation (shares)		67,182,000
Stock 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	167,796
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
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
Stock based compensation (shares)		7,984,000
Stock 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