Retirement Plans, Pension Plan Assets/Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Pension plan assets/investments [Abstract]
Acceptable ranges within which asset allocations will fluctuate	5.00%
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	$ 761,015	$ 659,426
Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	6,665	5,565
Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	$ 517,221	439,915
Equity Securities [Member]
Pension plan assets/investments [Abstract]
Target allocation percentage	50.00%
Fixed Income Securities and Cash [Member]
Pension plan assets/investments [Abstract]
Target allocation percentage	50.00%
US [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	$ 237,129	213,946	$ 213,628
US [Member] | Investments Measured at NAV [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	237,129	213,946
US [Member] | Global Equity Securities: Limited Partnership [Member] | Investments Measured at NAV [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	121,569	110,965
US [Member] | Fixed Income Securities: Commingled Trust Funds [Member] | Investments Measured at NAV [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	115,560	102,981
Non-US [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	523,886	445,480	$ 408,249
Non-US [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	6,665	5,565
Non-US [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	517,221	439,915
Non-US [Member] | U.S. Equities [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	51,882	36,842
Non-US [Member] | U.S. Equities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	0	0
Non-US [Member] | U.S. Equities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	51,882	36,842
Non-US [Member] | Non-U.S. Equities [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	124,496	103,460
Non-US [Member] | Non-U.S. Equities [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	0	0
Non-US [Member] | Non-U.S. Equities [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	124,496	103,460
Non-US [Member] | Balanced Managed Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	103,717	44,989
Non-US [Member] | Balanced Managed Funds [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	0	0
Non-US [Member] | Balanced Managed Funds [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	103,717	44,989
Non-US [Member] | Fixed Income Securities: Commingled Trust Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	238,027	257,565
Non-US [Member] | Fixed Income Securities: Commingled Trust Funds [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	1,444	3,431
Non-US [Member] | Fixed Income Securities: Commingled Trust Funds [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	236,583	254,134
Non-US [Member] | Real Estate/Other [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	543	490
Non-US [Member] | Real Estate/Other [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	0	0
Non-US [Member] | Real Estate/Other [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	543	490
Non-US [Member] | Cash and Cash Equivalents [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	5,221	2,134
Non-US [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	5,221	2,134
Non-US [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Fair value of plan assets	$ 0	$ 0