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Marketable Securities (Amortized Cost, Gross Unrealized Gains (Losses) And Fair Value Of Available-For-Sale Securities) (Details) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2011	Jan. 31, 2011	Oct. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 178,261	$ 472,268	$ 438,901
Unrealized Gains	600	651	1,188
Unrealized (Losses)	(3,066)	(4,511)	(3,809)
Fair Value	175,795	468,408	436,280
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	81,407	137,559
Municipal And Pre-Refunded Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	64,462	186,404	217,181
Federal Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,001	59,175	75,787
FDIC Insured Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value		23,555	41,679
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value		30,353	39,565
Certificate Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,969
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value		1,900	31,925
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	20,956	29,462	30,143
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	46,710	116,231	249,638
Unrealized Gains	27	198	445
Unrealized (Losses)	(88)	(9)	(5)
Fair Value	46,649	116,420	250,078
Short-Term Investments [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,846
Unrealized Gains	1
Unrealized (Losses)	(67)
Fair Value	15,780
Short-Term Investments [Member] | Municipal And Pre-Refunded Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,129	42,996	63,043
Unrealized Gains	25	48	99
Unrealized (Losses)	(21)	(9)	(5)
Fair Value	28,133	43,035	63,137
Short-Term Investments [Member] | Federal Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,000	40,842	73,592
Unrealized Gains	1	80	180
Fair Value	2,001	40,922	73,772
Short-Term Investments [Member] | FDIC Insured Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		23,489	41,528
Unrealized Gains		66	151
Fair Value		23,555	41,679
Short-Term Investments [Member] | Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		7,004	39,550
Unrealized Gains		4	15
Fair Value		7,008	39,565
Short-Term Investments [Member] | Certificate Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	735
Fair Value	735
Short-Term Investments [Member] | Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,900	31,925
Fair Value		1,900	31,925
Long-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	131,551	356,037	189,263
Unrealized Gains	573	453	743
Unrealized (Losses)	(2,978)	(4,502)	(3,804)
Fair Value	129,146	351,988	186,202
Long-Term Investments [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	65,626	137,540
Unrealized Gains	261	173
Unrealized (Losses)	(260)	(154)
Fair Value	65,627	137,559
Long-Term Investments [Member] | Municipal And Pre-Refunded Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36,041	143,711	153,409
Unrealized Gains	311	216	732
Unrealized (Losses)	(23)	(558)	(97)
Fair Value	36,329	143,369	154,044
Long-Term Investments [Member] | Federal Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		18,225	2,004
Unrealized Gains		30	11
Unrealized (Losses)		(2)
Fair Value		18,253	2,015
Long-Term Investments [Member] | Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		23,311
Unrealized Gains		34
Fair Value		23,345
Long-Term Investments [Member] | Certificate Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,234
Unrealized Gains	1
Unrealized (Losses)	(1)
Fair Value	6,234
Long-Term Investments [Member] | Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,650	33,250	33,850
Unrealized (Losses)	(2,694)	(3,788)	(3,707)
Fair Value	$ 20,956	$ 29,462	$ 30,143

X

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 7

-Footnote 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558



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-Publisher FASB

-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=6505594

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13, 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

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+ References

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