Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Liabilities:
Kolltan acquisition contingent consideration	$ 14,281	$ 13,779
Fair value \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	14,281	13,779
Fair Value Measurements. \| Level 2
Assets:
Money market funds and cash equivalents	13,867	15,755
Marketable securities	61,598	69,712
Total financial assets at fair value	75,465	85,467
Fair Value Measurements. \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	14,281	13,779
Total financial liabilities at fair value	14,281	13,779
Fair Value Measurements. \| Fair value
Assets:
Money market funds and cash equivalents	13,867	15,755
Marketable securities	61,598	69,712
Total financial assets at fair value	75,465	85,467
Liabilities:
Kolltan acquisition contingent consideration	14,281	13,779
Total financial liabilities at fair value	$ 14,281	$ 13,779

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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Amount of liability recognized arising from contingent consideration in a business combination.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of financial and nonfinancial obligations.

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Amount of investment in marketable security.

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