Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Certificates of deposit [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial paper [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Debt securities of government sponsored entities [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity index funds [Member]

Assets measured at fair value on a recurring basis

Total fair value

63,850

40,843

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member]

Assets measured at fair value on a recurring basis

Total fair value

420,554

419,824

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal bonds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]

Assets measured at fair value on a recurring basis

Total fair value

1,458,999

1,707,830

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Certificates of deposit [Member]

Assets measured at fair value on a recurring basis

Total fair value

157,372

223,111

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commercial paper [Member]

Assets measured at fair value on a recurring basis

Total fair value

86,482

199,181

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]

Assets measured at fair value on a recurring basis

Total fair value

576,313

566,724

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt securities of government sponsored entities [Member]

Assets measured at fair value on a recurring basis

Total fair value

220,879

290,543

^[1]

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Equity index funds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money market funds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Municipal bonds [Member]

Assets measured at fair value on a recurring basis

Total fair value

397,952

402,147

Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury securities [Member]

Assets measured at fair value on a recurring basis

Total fair value

20,001

26,124

^[1]

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]

Assets measured at fair value on a recurring basis

Total fair value

5,744

11,551

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Certificates of deposit [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Commercial paper [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt securities of government sponsored entities [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity index funds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money market funds [Member]

Assets measured at fair value on a recurring basis

Total fair value

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Municipal bonds [Member]

Assets measured at fair value on a recurring basis

Total fair value

5,744

11,551

Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury securities [Member]

Assets measured at fair value on a recurring basis

Total fair value

$ 0

[1]	The table has been corrected to reflect debt securities of government sponsored entities and U.S. Treasury securities as Level 2 within the fair value hierarchy. Previously, these instruments were reflected as Level 1.

- 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.

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- 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 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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