Description of the amortization method for debt discount or premium.

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Represents the percentage by which the market price of the debentures as a percentage of the value of the common stock into which the debentures are convertible must decline for the debentures to be convertible into common stock.

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Represents the percentage by which the market price of common stock must exceed the conversion price for the debentures to be convertible into common stock.

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Debt Instrument, Redemption Price

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Original term of term loan.

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Write-off of amounts previously recognized at the issuance of an instrument in an extinguishment of debt.

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The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period.

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

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The effective interest rate on the liability component of convertible debt instrument which may be settled in cash upon conversion, including partial cash settlement.

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Description of the conversion terms of a debt instrument which may include the conversion ratio (including all potential conversion ratios if contingently adjustable), type of debt or equity security into which the debt is convertible, the dollars of debt or the number of shares into which the instrument is convertible (or potentially convertible into), the conversion period, any contingencies associated with the conversion terms, and the existence and amount of a beneficial conversion feature.

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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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Description of the frequency of periodic payments (monthly, quarterly, annual).

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The average effective interest rate during the reporting period.

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Interest rate stated in the contractual debt agreement.

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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.

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Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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Amount of the required periodic payments applied to principal.

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Gross amount of debt extinguished.

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Amount represents the difference between the fair value of the payments made and the carrying amount of the debt at the time of its extinguishment.

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Reflects the difference between the fair value of payments made to legally extinguish a debt and its carrying value at that time. This item excludes the write-off of amounts previously capitalized as debt issuance costs.

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Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

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Notes Payable - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended	1 Months Ended		6 Months Ended				1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended	1 Months Ended
	Jul. 31, 2011	Jul. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Apr. 30, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Jul. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Jul. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2018	Jul. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2021	Jul. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2026	Mar. 31, 2006 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jul. 31, 2011 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jul. 31, 2010 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Apr. 30, 2010 Term Loan due 2013	Jul. 31, 2011 Term Loan due 2013	Nov. 30, 2009 Other Notes Payable
Debt Instrument [Line Items]
Loan expiration period, in years											3Y
Issued Debt			$ 253,000					$ 200,000			$ 20,000
Term Loan, fixed principal amount											500
Description of interest payment period			Interest on the 4.00% Debentures is payable semi-annually in April and October.					Interest on the 6.25% Debentures was payable semi-annually in March and September.			Accrued interest payments were payable quarterly in February, May, August, and November.
Convertible debentures to common stock, conversion price		$ 20.538		$ 20.538
Convertible debentures to common stock, total number of share		12,319
Circumstances for the redemption of Debentures				The market price of our common stock exceeding 120% of the conversion price; A call for redemption of the 4.00% Debentures; Specified distributions to holders of our common stock; If a fundamental change, such as a change of control, occurs; During the two months prior to, but not on, the maturity date; or The market price of the 4.00% Debentures declining to less than 98% of the value of the common stock into which the 4.00% Debentures are convertible.
Market price of common stock exceeding percent of the conversion price				120.00%
Market price of debentures declining to maximum percent of the value of the common stock				98.00%
Description of amortization of debt discount				The unamortized debt discount will be amortized to interest expense using the effective interest method through March 2018.
Redemption price					100.00%	100.00%	100.00%
Debt effective interest rate				7.25%					8.60%	8.60%
Redeemed amount of debt									196,509			18,500
Loss on early extinguishment of debt before tax	(3,518)								11,192			312
Write-off of net unamortized debt discount									6,190
Debt effective interest rate												4.81%
Premium on redemption									3,518
Write-off of unamortized debt issuance costs									$ 1,484
Interest rate													3.875%
Other Notes Payable, due date													Nov. 17, 2012