Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an 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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Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Original maturity period for highly liquid investments to be considered cash equivalent, maximum

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Likelihood of realization percentage used in determining value of recognized income tax positions.

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Portion of commitments related to research and development arrangements with third parties which has not yet been incurred.

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Summary of Significant Accounting Policies - Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2015 Segment Entity	Mar. 31, 2014	Dec. 31, 2014 Entity
Organization And Significant Accounting Policies [Line Items]
Research and development commitments with third parties not incurred	$ 6,828,000		$ 2,183,000
Maturity period of liquid investment	3 months
Cash equivalent investments in highly liquid money market accounts	87,768,000us-gaap_MoneyMarketFundsAtCarryingValue		16,598,000us-gaap_MoneyMarketFundsAtCarryingValue
Number of collaborators over which the Company has significant influence	2xon_NumberOfCollaborators		2xon_NumberOfCollaborators
Fair value of financial assets measured at fair value on a recurring basis	387,188,000us-gaap_AssetsFairValueDisclosure		280,497,000us-gaap_AssetsFairValueDisclosure
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	115,454,000	21,922,000
Variable interest entities, risk of loss	192,228,000		0
Percentage of recognized income tax positions	50.00%
Number of segment	1us-gaap_NumberOfOperatingSegments
Revenues	33,849,000us-gaap_Revenues	7,854,000us-gaap_Revenues
Foreign Countries
Organization And Significant Accounting Policies [Line Items]
Long-lived assets	82,133,000		17,100,000
Revenues	1,290,000	0
Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	294,922,000		164,889,000
Oragenics, Inc.
Organization And Significant Accounting Policies [Line Items]
Company's ownership percentage	22.40%		24.40%
Oragenics, Inc. \| Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	8,128,000		7,192,000
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	936,000	710,000
ZIOPHARM Oncology, Inc.
Organization And Significant Accounting Policies [Line Items]
Company's ownership percentage	13.90%		15.70%
ZIOPHARM Oncology, Inc. \| Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	192,032,000		83,099,000
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	$ 96,334,000	$ 3,934,000
Minimum
Organization And Significant Accounting Policies [Line Items]
Weighted Average Useful Life (Years)	2 years
Minimum \| Leasehold Improvements
Organization And Significant Accounting Policies [Line Items]
Property plant and equipment, useful life	1 year
Maximum
Organization And Significant Accounting Policies [Line Items]
Weighted Average Useful Life (Years)	14 years
Maximum \| Leasehold Improvements
Organization And Significant Accounting Policies [Line Items]
Property plant and equipment, useful life	14 years