Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of Cash, Cash Equivalents and Restricted Investment
Amortized Cost	$ 114,528	$ 99,126
Unrealized Gain (Loss)
Estimated Fair Value	114,528	99,126
Cash [Member]
Summary of Cash, Cash Equivalents and Restricted Investment
Amortized Cost	2,967	3,569
Unrealized Gain (Loss)
Estimated Fair Value	2,967	3,569
Certificates of Deposit [Member]
Summary of Cash, Cash Equivalents and Restricted Investment
Amortized Cost	310	310
Unrealized Gain (Loss)
Estimated Fair Value	310	310
Money Market Funds [Member]
Summary of Cash, Cash Equivalents and Restricted Investment
Amortized Cost	111,251	95,247
Unrealized Gain (Loss)
Estimated Fair Value	111,251	95,247
Cash and Cash Equivalents [Member]
Summary of Cash, Cash Equivalents and Restricted Investment
Estimated Fair Value	114,218	98,816
Restricted Investment [Member]
Summary of Cash, Cash Equivalents and Restricted Investment
Estimated Fair Value	$ 310	$ 310

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.

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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 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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