3% Convertible Senior Notes (Details) (USD $)	3 Months Ended
Oct. 31, 2013	Jul. 31, 2009
Debt Disclosure [Abstract]
Debt instrument, issuance date		May 08, 2009
Debt instrument, face amount		$ 200,000,000
Net proceeds from debt issuance		194,541,000
Aggregate amount of initial purchasers' discount and other transaction costs related to debt issuance		5,459,000
Debt instrument, interest rate, stated percentage		3.00%
Date of record	Oct. 18, 2013
Date declared	Oct. 03, 2013
Debt instrument, convertible, conversion price	$ 32.15
Debt instrument, convertible, conversion ratio	31.1038
Original principal amount of each 3.0% convertible senior note	$ 1,000
Debt instrument, call date, earliest	May 05, 2014
Debt instrument, first put date	May 01, 2014
Debt instrument, second put date	May 01, 2019
Debt instrument, third put date	May 01, 2024
Debt instrument, maturity date	May 01, 2029

Aggregate amount of initial purchasers' discount and other transaction costs related to debt issuance.

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The first scheduled date that the holders of the convertible senior notes can require issuer to repurchase some or all of the outstanding convertible senior notes solely for cash.

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The second scheduled date that the holders of the convertible senior notes can require issuer to repurchase some or all of the outstanding convertible senior notes solely for cash.

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The third scheduled date that the holders of the convertible senior notes can require issuer to repurchase some or all of the outstanding convertible senior notes solely for cash.

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Original principal amount of each 3.0% convertible senior note.

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Earliest date before maturity when the issuer can call the outstanding debt instrument for repayment or conversion to equity, in CCYY-MM-DD format.

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The price per share of the conversion feature embedded in the debt instrument.

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The ratio applied to the debt for purposes of determining the number of shares of the equity security into which the debt will be converted.

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The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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Interest rate stated in the contractual debt agreement.

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Date the debt instrument was issued, in CCYY-MM-DD format.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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