Fair Value Measurements Other (Details) - Significant unobservable inputs (Level 3) - Discounted cash flow - Auction rate securities	12 Months Ended
Apr. 30, 2018
Fair Value Inputs
Coupon rates (as a percent)	2.80%
Minimum
Fair Value Inputs
Estimated redemption periods	1 year
Discount rates (as a percent)	3.60%
Maximum
Fair Value Inputs
Estimated redemption periods	16 years
Discount rates (as a percent)	9.80%

Represents the coupon rate used as an input to measure fair value.

No definition available.

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- Definition

Represents the estimated redemption period used as an input to measure fair value.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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