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Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013	Jan. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 378,393	$ 219,036
Unrealized Gains	438	627
Unrealized (Losses)	(760)	(2,896)
Fair Value	378,071	216,767
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	228,286	89,736
Unrealized Gains	242	156
Unrealized (Losses)	(42)	(38)
Fair Value	228,486	89,854
Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	150,107	129,300
Unrealized Gains	196	471
Unrealized (Losses)	(718)	(2,858)
Fair Value	149,585	126,913
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	152,775	95,935
Corporate Bonds | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	88,432	34,899
Unrealized Gains	106	7
Unrealized (Losses)	(23)	(28)
Fair Value	88,515	34,878
Corporate Bonds | Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,219	60,852
Unrealized Gains	102	277
Unrealized (Losses)	(61)	(72)
Fair Value	64,260	61,057
Municipal And Pre-Refunded Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	116,364	60,234
Municipal And Pre-Refunded Municipal Bonds | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	63,355	41,519
Unrealized Gains	85	135
Unrealized (Losses)	(17)	(10)
Fair Value	63,423	41,644
Municipal And Pre-Refunded Municipal Bonds | Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,925	18,410
Unrealized Gains	76	186
Unrealized (Losses)	(60)	(6)
Fair Value	52,941	18,590
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Fair Value	43,235	12,194
Certificates of Deposit | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,870	5,225
Unrealized Gains	25
Fair Value	40,895	5,225
Certificates of Deposit | Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,340	6,970
Unrealized (Losses)		(1)
Fair Value	2,340	6,969
US Treasury Bill Securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	41,105	14,988
US Treasury Bill Securities | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,354
Unrealized Gains	14
Fair Value	21,368
US Treasury Bill Securities | Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,724	14,982
Unrealized Gains	13	6
Fair Value	19,737	14,988
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	10,781	3,592
Commercial Paper | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,775	3,580
Unrealized Gains	8	12
Unrealized (Losses)	(2)
Fair Value	10,781	3,592
US Government Corporations and Agencies Securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	9,481	9,627
US Government Corporations and Agencies Securities | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,500	4,513
Unrealized Gains	4	2
Fair Value	3,504	4,515
US Government Corporations and Agencies Securities | Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,974	5,111
Unrealized Gains	5	2
Unrealized (Losses)	(2)	(1)
Fair Value	5,977	5,112
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	4,330	20,197
Auction Rate Securities | Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,925	22,975
Unrealized (Losses)	(595)	(2,778)
Fair Value	$ 4,330	$ 20,197

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 Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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-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 3: 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.

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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 Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558



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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-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 Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563



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-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.

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+ References

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