Fair Value Of Financial Assets And Financial Liabilities (Financial Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands	Jul. 31, 2011	Jan. 31, 2011	Jul. 31, 2010
Financial assets accounted for at fair value on a recurring basis	$ 382,249	$ 468,408	$ 503,714
Auction Rate Securities [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis
Corporate Bonds [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis	145,121	137,559
Municipal And Pre-Refunded Municipal Bonds [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis
Federal Government Agencies [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis	57,404	59,175	174,550
FDIC Insured Corporate Bonds [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis	4,004	23,555	41,831
Treasury Bills [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis	19,829	30,353	49,667
Certificate Of Deposit [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis	5,143
Variable Rate Demand Notes [Member] \| Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis
Level 1 [Member]
Financial assets accounted for at fair value on a recurring basis	231,501	250,642	266,048
Auction Rate Securities [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis
Corporate Bonds [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis
Municipal And Pre-Refunded Municipal Bonds [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis	124,343	186,404	195,784
Federal Government Agencies [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis
FDIC Insured Corporate Bonds [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis
Treasury Bills [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis
Certificate Of Deposit [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis
Variable Rate Demand Notes [Member] \| Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis	2,901	1,900	10,425
Level 2 [Member]
Financial assets accounted for at fair value on a recurring basis	127,244	188,304	206,209
Auction Rate Securities [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis	23,504	29,462	31,457
Corporate Bonds [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
Municipal And Pre-Refunded Municipal Bonds [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
Federal Government Agencies [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
FDIC Insured Corporate Bonds [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
Treasury Bills [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
Certificate Of Deposit [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
Variable Rate Demand Notes [Member] \| Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis
Level 3 [Member]
Financial assets accounted for at fair value on a recurring basis	23,504	29,462	31,457
Corporate Bonds [Member]
Financial assets accounted for at fair value on a recurring basis	145,121	137,559
Municipal And Pre-Refunded Municipal Bonds [Member]
Financial assets accounted for at fair value on a recurring basis	124,343	186,404	195,784
Federal Government Agencies [Member]
Financial assets accounted for at fair value on a recurring basis	57,404	59,175	174,550
Auction Rate Securities [Member]
Financial assets accounted for at fair value on a recurring basis	23,504	29,462	31,457
Treasury Bills [Member]
Financial assets accounted for at fair value on a recurring basis	19,829	30,353	49,667
Certificate Of Deposit [Member]
Financial assets accounted for at fair value on a recurring basis	5,143
FDIC Insured Corporate Bonds [Member]
Financial assets accounted for at fair value on a recurring basis	4,004	23,555	41,831
Variable Rate Demand Notes [Member]
Financial assets accounted for at fair value on a recurring basis	$ 2,901	$ 1,900	$ 10,425

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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