Long-Term Debt (Components of Long-Term Debt) (Details) - USD ($) $ in Thousands	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018
Debt Instrument [Line Items]
Capital lease obligation	$ 0
Capital lease obligation		$ 0	$ 5,376
Debt issuance costs and discounts	(6,711)	(7,371)	(9,332)
Long-term debt including current portion	1,493,289	1,492,629	1,496,044
Less: Current portion	0	0	(1,038)
Long-term debt excluding current portion	$ 1,493,289	1,492,629	1,495,006
Senior Notes \| Senior Notes, 4.125%, due October 2020
Debt Instrument [Line Items]
Interest rate	4.125%
Senior notes	$ 650,000	650,000	650,000
Senior Notes \| Senior Notes, 5.500%, due November 2022
Debt Instrument [Line Items]
Interest rate	5.50%
Senior notes	$ 500,000	500,000	500,000
Senior Notes \| Senior Notes, 5.250%, due October 2025
Debt Instrument [Line Items]
Interest rate	5.25%
Senior notes	$ 350,000	$ 350,000	$ 350,000

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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