CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - UNAUDITED - USD ($) $ in Thousands	Common Stock [Member] Class A [Member]	Common Stock [Member] Class B [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Class A [Member]	Additional Paid-in Capital [Member] Class B [Member]	Retained Earnings [Member]	Retained Earnings [Member] Class A [Member]	Retained Earnings [Member] Class B [Member]	Accumulated Other Comprehensive Loss, Net of Tax [Member]	Accumulated Other Comprehensive Loss, Net of Tax [Member] Class A [Member]	Accumulated Other Comprehensive Loss, Net of Tax [Member] Class B [Member]	Treasury Stock [Member]	Treasury Stock [Member] Class A [Member]	Treasury Stock [Member] Class B [Member]	Total	Class A [Member]	Class B [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member] Common Stock [Member] Class A [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member] Common Stock [Member] Class B [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member] Additional Paid-in Capital [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member] Retained Earnings [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member] Accumulated Other Comprehensive Loss, Net of Tax [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member] Treasury Stock [Member]	Cumulative Effect of Change in Accounting Principle, Net of Tax [Member]
Balance at Apr. 30, 2020	$ 70,166	$ 13,016	$ 431,680			$ 1,780,129			$ (575,497)			$ (785,870)			$ 933,624			$ 0	$ 0	$ 0	$ (1,390)	$ 0	$ 0	$ (1,390)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted shares issued under stock-based compensation plans	0	0	(5,121)			1			0			5,184			64
Impact of tax withholding on stock-based compensation and other	0	0	368			0			0			(1,687)			(1,319)
Stock-based compensation expense	0	0	4,314			0			0			0			4,314
Common stock dividends	0	0		$ 0	$ 0		$ (16,149)	$ (3,112)		$ 0	$ 0		$ 0	$ 0		$ (16,149)	$ (3,112)
Common stock class conversions	11	(11)	0			0			0			0			0
Comprehensive income, net of tax	0	0	0			16,334			41,379			0			57,713
Balance at Jul. 31, 2020	70,177	13,005	431,241			1,775,813			(534,118)			(782,373)			973,745
Balance at Apr. 30, 2021	70,208	12,974	444,358			1,850,058			(490,790)			(795,517)			1,091,291
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted shares issued under stock-based compensation plans	0	0	(6,342)			(3)			0			6,409			64
Impact of tax withholding on stock-based compensation and other	0	0	310			0			0			(4,470)			(4,160)
Stock-based compensation expense	0	0	7,364			0			0			0			7,364
Purchase of treasury shares	0	0	0			0			0			(7,367)			(7,367)
Common stock dividends	0	0		$ 0	$ 0		$ (16,185)	$ (3,122)		$ 0	$ 0		$ 0	$ 0		$ (16,185)	$ (3,122)
Common stock class conversions	3	(3)	0			0			0			0			0
Comprehensive income, net of tax	0	0	0			13,830			(3,810)			0			10,020
Balance at Jul. 31, 2021	$ 70,211	$ 12,971	$ 445,690			$ 1,844,578			$ (494,600)			$ (800,945)			$ 1,077,905