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	Treasury Stock
Beginning Balances, Shares at Apr. 30, 2014		316,628				42,400
Beginning Balances, Value at Apr. 30, 2014	$ 1,556,549	$ 3,166	$ 766,654	$ 5,177	$ 1,589,297	$ (807,745)
Net income	473,663				473,663
Other comprehensive loss	(3,437)			(3,437)
Stock-based compensation	26,068		26,068
Stock-based awards exercised or vested, value	16,131		(8,881)		(942)	$ 25,954
Stock-based awards exercised or vested, shares						1,359
Acquisition of treasury shares, shares						(315)
Acquisition of treasury shares, value	(10,449)					$ (10,449)
Other, value	(5,616)		(48)		(5,616)	$ 48
Other, shares						3
Cash dividends declared	(219,960)				(219,960)
Ending Balances, Shares at Apr. 30, 2015		316,628				41,353
Ending Balances, Value at Apr. 30, 2015	1,832,949	$ 3,166	783,793	1,740	1,836,442	$ (792,192)
Net income	374,267				374,267
Other comprehensive loss	(12,973)			(12,973)
Stock-based compensation	23,540		23,540
Stock-based awards exercised or vested, value	25,346		(15,257)		(2,848)	$ 43,451
Stock-based awards exercised or vested, shares						2,262
Acquisition of treasury shares, shares						(610)
Acquisition of treasury shares, value	(18,102)					$ (18,102)
Repurchase and retirement of common shares, shares		(56,409)
Repurchase and retirement of common shares, value	(2,000,236)	$ (564)	(33,846)		(1,965,826)
Cash dividends declared	(201,688)				(201,688)
Ending Balances, Shares at Apr. 30, 2016		260,219				39,701
Ending Balances, Value at Apr. 30, 2016	23,103	$ 2,602	758,230	(11,233)	40,347	$ (766,843)
Net income	408,945				408,945
Other comprehensive loss	(4,066)			(4,066)
Stock-based compensation	19,285		19,285
Stock-based awards exercised or vested, value	1,815		(14,191)		(1,915)	$ 17,921
Stock-based awards exercised or vested, shares						928
Acquisition of treasury shares, shares						(255)
Acquisition of treasury shares, value	(5,830)					$ (5,830)
Repurchase and retirement of common shares, shares		(14,020)
Repurchase and retirement of common shares, value	(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)