Fair Value Measurements (Details 3) (Significant unobservable inputs (Level 3), Discounted cash flow)	12 Months Ended
Apr. 30, 2013
Auction rate securities \| Minimum
Fair Value Inputs
Coupon rates (as a percent)	0.30%
Estimated redemption periods	6 years
Discount rates (as a percent)	7.40%
Auction rate securities \| Maximum
Fair Value Inputs
Coupon rates (as a percent)	0.40%
Estimated redemption periods	21 years
Discount rates (as a percent)	18.90%
Convertible bonds
Fair Value Inputs
Coupon rates (as a percent)	5.00%
Estimated redemption periods	5 years
Discount rates (as a percent)	6.30%

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.

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=7578670&loc=d3e19207-110258

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