3% Convertible Senior Notes (Details) (USD $)	3 Months Ended	6 Months Ended
Jul. 31, 2009	Jan. 31, 2013
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%
Debt Instrument, convertible, conversion price		$ 33.19
Debt Instrument, convertible, conversion ratio		30.1255
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.

No definition available.

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- Definition

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.

+ References

No definition available.

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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.

+ References

No definition available.

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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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No definition available.

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- Definition

Original principal amount of each 3.0% convertible senior note.

+ References

No definition available.

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- Definition

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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- Definition

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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- Definition

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

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