Cash, Cash Equivalents and Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Cash, Cash Equivalents and Marketable Securities
Marketable securities, Unrealized gains	8
Cash, cash equivalents and marketable securities, unrealized gains	8	3
Cost
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	29,442	30,075
Marketable securities	25,689
Total cash, cash equivalents and marketable securities	55,131	39,722
Fair Value
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	29,442	30,075
Marketable securities	25,697
Total cash, cash equivalents and marketable securities	55,139	39,725
Corporate debt securities due within 1 year of date of purchase
Cash, Cash Equivalents and Marketable Securities
Marketable securities, Unrealized gains	7	3
Corporate debt securities due within 1 year of date of purchase \| Cost
Cash, Cash Equivalents and Marketable Securities
Marketable securities	23,191	9,647
Corporate debt securities due within 1 year of date of purchase \| Fair Value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities	23,198	9,650
Government-sponsored entities due within 1 year of date of purchase
Cash, Cash Equivalents and Marketable Securities
Marketable securities, Unrealized gains	1
Government-sponsored entities due within 1 year of date of purchase \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities	2,499
Government-sponsored entities due within 1 year of date of purchase \| Cost
Cash, Cash Equivalents and Marketable Securities
Marketable securities	2,498
Cash and money market funds \| Cost
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	23,194	25,326
Cash and money market funds \| Fair Value \| Level 1
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	23,194	25,326
Corporate debt securities due within 3 months of date of purchase \| Cost
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	6,248
Corporate debt securities due within 3 months of date of purchase \| Fair Value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	6,248
Government-sponsored entities and corporate debt securities due within 3 months of date of purchase \| Cost
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents		4,749
Government-sponsored entities and corporate debt securities due within 3 months of date of purchase \| Fair Value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents		4,749
Maximum \| Corporate debt securities due within 1 year of date of purchase
Cash, Cash Equivalents and Marketable Securities
Maturity period from date of purchase to classify an investment as marketable securities	1 year	1 year
Maximum \| Corporate debt securities due within 3 months of date of purchase
Cash, Cash Equivalents and Marketable Securities
Maturity period from date of purchase to classify an investment as cash and cash equivalents	3 months
Maximum \| Government-sponsored entities and corporate debt securities due within 3 months of date of purchase
Cash, Cash Equivalents and Marketable Securities
Maturity period from date of purchase to classify an investment as cash and cash equivalents		3 months

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 item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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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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- Definition

Cash 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 customer may deposit additional funds at any time and 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. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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