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Fair Value - Additional Information (Detail) (USD $)	3 Months Ended
	Apr. 30, 2013	Jan. 31, 2013	Apr. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available-for-sale securities	$ 364,709,000	$ 378,071,000	$ 208,287,000
Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available-for-sale securities	149,771,000	149,585,000	91,231,000
Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from sale of available-for-sale securities	4,600,000
Estimated fair value of available-for-sale securities		4,330,000	4,330,000
Auction Rate Securities | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Par value of available-for-sale securities		4,900,000	4,900,000
Estimated fair value of available-for-sale securities		4,330,000	4,330,000
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available-for-sale securities		4,330,000	4,330,000
Fair Value, Inputs, Level 3 | Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from sale of available-for-sale securities	4,600,000
Estimated fair value of available-for-sale securities		4,330,000	4,330,000
Fair Value, Inputs, Level 3 | Auction Rate Securities | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Par value of available-for-sale securities		$ 4,900,000	$ 4,900,000

X

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

-Name Accounting Standards Codification

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X

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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X

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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