Convertible Notes Payable - Summary of Notes Due 2020 (Details) (4.0% Convertible Senior Notes due December 15, 2020 [Member], USD $) In Thousands, unless otherwise specified	Apr. 30, 2014
Debt Instrument [Line Items]
Interest rate on convertible notes	4.00%
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Liability component, Principal balance	$ 192,216
Liability component, Unamortized discount	15,575
Liability component, Net carrying amount	176,641
Equity component, Net carrying amount	$ 43,131

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.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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

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The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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