Long-Term Debt (Details)	Jan. 31, 2017 USD ($)	Apr. 30, 2016 USD ($)	Jan. 31, 2016 USD ($)
Debt Instrument [Line Items]
Long-term debt	$ 2,593,564,000	$ 1,492,201,000	$ 2,616,640,000
Less: Current portion	(942,000)	(826,000)	(817,000)
Long-term debt excluding current portion	2,592,622,000	1,491,375,000	2,615,823,000
Long-term Line of Credit	1,100,000,000	0	1,125,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2,000,000,000.0
Available increase in borrowing capacity	$ 500,000,000.0
Maximum quarterly debt-to-EBITDA ratio	3.50
Maximum annual debt-to-EBITDA ratio	4.50
Minimum interest coverage ratio	2.50
Swingline Loans [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 200,000,000.0
Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	50,000,000.0
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Long-term debt	6,820,000	7,435,000	7,637,000
Unamortized Debt Issuance Expense	(13,256,000)	(15,234,000)	(15,997,000)
Senior Notes due 2020 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	650,000,000	650,000,000	650,000,000
Senior Notes due 2022 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	500,000,000	500,000,000	500,000,000
Senior Notes due 2025 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 350,000,000	$ 350,000,000	$ 350,000,000

Debt Instrument, Covenant, Annual Debt To EBITDA Ratio

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Debt Instrument, Covenant, Interest Coverage Ratio

+ References

No definition available.

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- Definition

Debt Instrument, Covenant, Quarterly Debt To EBITDA Ratio

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No definition available.

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- Definition

Line Of Credit Facility, Available Increase In Borrowing Capacity

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No definition available.

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- Definition

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

+ References

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Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

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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