Fair Value of Financial Instruments - Schedule of Fair Value Assets Measured on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	May 03, 2015 companies	Apr. 27, 2014
Fair Value Disclosures [Abstract]
Minority investments	$ 2,847fnsr_MinorityInvestment	$ 2,117fnsr_MinorityInvestment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Minority Investments, Number of Companies	2
Recurring \| Carrying Amount
Financial assets [Abstract]
Total	292,944	240,091
Recurring \| Carrying Amount \| Money Market Funds
Financial assets [Abstract]
Cash and cash equivalents	196	30,169
Recurring \| Carrying Amount \| Commercial Paper
Financial assets [Abstract]
Investments	0	89,922
Recurring \| Carrying Amount \| Certificates of Deposit
Financial assets [Abstract]
Investments	292,748	120,000
Recurring \| Fair Value
Financial assets [Abstract]
Total	292,944	240,091
Recurring \| Fair Value \| Level 1
Financial assets [Abstract]
Total	196	30,169
Recurring \| Fair Value \| Level 2
Financial assets [Abstract]
Total	292,748	209,922
Recurring \| Fair Value \| Level 3
Financial assets [Abstract]
Total	0	0
Recurring \| Fair Value \| Money Market Funds
Financial assets [Abstract]
Cash and cash equivalents	196	30,169
Recurring \| Fair Value \| Money Market Funds \| Level 1
Financial assets [Abstract]
Cash and cash equivalents	196	30,169
Recurring \| Fair Value \| Money Market Funds \| Level 2
Financial assets [Abstract]
Cash and cash equivalents	0	0
Recurring \| Fair Value \| Money Market Funds \| Level 3
Financial assets [Abstract]
Cash and cash equivalents	0	0
Recurring \| Fair Value \| Commercial Paper
Financial assets [Abstract]
Investments	0	89,922
Recurring \| Fair Value \| Commercial Paper \| Level 1
Financial assets [Abstract]
Investments	0	0
Recurring \| Fair Value \| Commercial Paper \| Level 2
Financial assets [Abstract]
Investments	0	89,922
Recurring \| Fair Value \| Commercial Paper \| Level 3
Financial assets [Abstract]
Investments	0	0
Recurring \| Fair Value \| Certificates of Deposit
Financial assets [Abstract]
Investments	292,748	120,000
Recurring \| Fair Value \| Certificates of Deposit \| Level 1
Financial assets [Abstract]
Investments	0	0
Recurring \| Fair Value \| Certificates of Deposit \| Level 2
Financial assets [Abstract]
Investments	292,748	120,000
Recurring \| Fair Value \| Certificates of Deposit \| Level 3
Financial assets [Abstract]
Investments	$ 0	$ 0

This item including the cost method and equity method investments

No definition available.

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- Definition

Minority Investments, Number of Companies

+ References

No definition available.

+ Details

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: 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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph a, f, g

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

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