Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Apr. 01, 2012
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 170,922	$ 190,535
U.S. government treasuries and agencies securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	145,816	156,331
Gross Unrealized Gains	19	8
Gross Unrealized Losses	0	(24)
Estimated Fair Value	145,835	156,315
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	62,100	104,596
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value	62,100	104,596
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	13,678	21,485
Gross Unrealized Gains	18	59
Gross Unrealized Losses	0	(6)
Estimated Fair Value	13,696	21,538
International government bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	4,606	4,650
Gross Unrealized Gains		1
Gross Unrealized Losses	(1)	(3)
Estimated Fair Value	4,605	4,648
Corporate commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,000	3,148
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value	1,000	3,148
Bank deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	11,183	11,633
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value	11,183	11,633
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		652
Gross Unrealized Gains		1
Gross Unrealized Losses
Estimated Fair Value		653
Total available-for-sale investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	238,383	302,495
Gross Unrealized Gains	37	69
Gross Unrealized Losses	(1)	(33)
Estimated Fair Value	238,419	302,531
Less amounts classified as cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	67,497	111,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	67,497	111,996
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	170,886	190,499
Gross Unrealized Gains	37	69
Gross Unrealized Losses	(1)	(33)
Estimated Fair Value	$ 170,922	$ 190,535

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+ Details

Investments in debt and equity securities which are categorized neither as trading securities nor held-to-maturity securities and which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

Reference 2: 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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-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 5: 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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13, 17

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 43

-Chapter 3

-Section A

-Paragraph 4, 5

-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 9: 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=6379932&loc=d3e22054-111558

+ Details

- 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+ Details