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 [Member]	Accumulated Other Comprehensive Loss [Member] Class A [Member]	Accumulated Other Comprehensive Loss [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, Period of Adoption, Adjustment [Member] Common Stock [Member] Class A [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock [Member] Class B [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Accumulated Other Comprehensive Loss [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Treasury Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]
Balance at Apr. 30, 2019	$ 70,127	$ 13,055	$ 422,305			$ 1,931,074			$ (508,738)			$ (746,476)			$ 1,181,347
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted Shares Issued under Stock-based Compensation Plans	0	0	(2,112)			(1)			0			2,219			106
Net Proceeds (Payments) from Exercise of Stock Options and Other	0	0	107			0			0			(1,244)			(1,137)
Stock-based Compensation Expense	0	0	4,604			0			0			0			4,604
Purchase of Treasury Shares	0	0	0			0			0			(10,000)			(10,000)
Common Stock Dividends	0	0		$ 0	$ 0		$ (16,148)	$ (3,104)		$ 0	$ 0		$ 0	$ 0		$ (16,148)	$ (3,104)
Common Stock Class Conversions	12	(12)	0			0			0			0			0
Comprehensive Income (Loss), Net of Tax	0	0	0			3,624			(27,286)			0			(23,662)
Balance at Jul. 31, 2019	70,139	13,043	424,904			1,915,445			(536,024)			(755,501)			1,132,006
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
Net Proceeds (Payments) from Exercise of Stock Options 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 (Loss), 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