Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Apr. 01, 2012
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	$ 380,951	$ 373,439
Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Cash and cash equivalents	103,465	164,516
Marketable securities	380,951	373,439
Total assets at fair value disclosure	484,416	537,955
U.S. Government and agency securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	130,138	141,859
Corporate debt obligations [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	168,590	167,668
Asset and mortgage-backed securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	52,130	46,594
Municipal bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	30,093	16,568
Other debt securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities		750
Fair Value Measurements Using, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Cash and cash equivalents	103,045	162,266
Marketable securities	130,138	141,859
Total assets at fair value disclosure	233,183	304,125
Fair Value Measurements Using, Level 1 [Member] \| U.S. Government and agency securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	130,138	141,859
Fair Value Measurements Using, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Cash and cash equivalents	420	2,250
Marketable securities	250,813	231,580
Total assets at fair value disclosure	251,233	233,830
Fair Value Measurements Using, Level 2 [Member] \| Corporate debt obligations [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	168,590	167,668
Fair Value Measurements Using, Level 2 [Member] \| Asset and mortgage-backed securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	52,130	46,594
Fair Value Measurements Using, Level 2 [Member] \| Municipal bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities	30,093	16,568
Fair Value Measurements Using, Level 2 [Member] \| Other debt securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities		750
Fair Value Measurements Using, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Cash and cash equivalents
Marketable securities
Total assets at fair value disclosure
Fair Value Measurements Using, Level 3 [Member] \| U.S. Government and agency securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities
Fair Value Measurements Using, Level 3 [Member] \| Corporate debt obligations [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities
Fair Value Measurements Using, Level 3 [Member] \| Asset and mortgage-backed securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities
Fair Value Measurements Using, Level 3 [Member] \| Municipal bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities
Fair Value Measurements Using, Level 3 [Member] \| Other debt securities [Member] \| Fair Value, Measurements, Recurring [Member]
Schedule of Assets Measured at Fair Value on a Recurring Basis
Marketable securities

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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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 includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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