Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Deficit)	Treasury Stock
Beginning Balances, Shares at Apr. 30, 2016		260,219				39,701
Beginning Balances, Value at Apr. 30, 2016	$ 23,103	$ 2,602	$ 758,230	$ (11,233)	$ 40,347	$ (766,843)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	408,945				408,945
Other comprehensive (loss) income	(4,066)			(4,066)
Stock-based compensation	19,285		19,285
Stock-based awards exercised or vested, shares						928
Stock-based awards exercised or vested	1,815		(14,191)		(1,915)	$ 17,921
Acquisition of treasury shares, shares						(255)
Acquisition of treasury shares	(5,830)					$ (5,830)
Repurchase and retirement of common shares, shares		14,020
Repurchase and retirement of common shares	(317,020)	$ (140)	(8,412)		(308,468)
Cash dividends declared	(187,115)				(187,115)
Ending Balances, Shares at Apr. 30, 2017		246,199				39,028
Ending Balances, Value at Apr. 30, 2017	(60,883)	$ 2,462	754,912	(15,299)	(48,206)	$ (754,752)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	613,149				613,149
Other comprehensive (loss) income	996			996
Stock-based compensation	21,713		21,713
Stock-based awards exercised or vested, shares						2,389
Stock-based awards exercised or vested	28,352		(16,375)		(1,494)	$ 46,221
Acquisition of treasury shares, shares						(306)
Acquisition of treasury shares	(9,147)					$ (9,147)
Cash dividends declared	(200,469)				(200,469)
Ending Balances, Shares at Apr. 30, 2018		246,199				36,945
Ending Balances, Value at Apr. 30, 2018	393,711	$ 2,462	760,250	(14,303)	362,980	$ (717,678)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	422,509				422,509
Other comprehensive (loss) income	(6,113)			(6,113)
Stock-based compensation	23,510		23,510
Stock-based awards exercised or vested, shares						787
Stock-based awards exercised or vested	2,333		(11,407)		(1,550)	$ 15,290
Acquisition of treasury shares, shares						(219)
Acquisition of treasury shares	(5,074)					$ (5,074)
Repurchase and retirement of common shares, shares		(7,862)
Repurchase and retirement of common shares	(184,838)	$ (79)	(4,717)		(180,042)
Cash dividends declared	(205,461)				(205,461)
Ending Balances, Shares at Apr. 30, 2019		238,337				36,377
Ending Balances, Value at Apr. 30, 2019	$ 541,527	$ 2,383	$ 767,636	$ (20,416)	$ 499,386	$ (707,462)