Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair value measurements
Restricted cash	$ 603	$ 603
Headquarters and laboratory facilities, South San Francisco, lease signed April 2015
Fair value measurements
Restricted cash	603	603
Level I \| Headquarters and laboratory facilities, South San Francisco, lease signed April 2015
Fair value measurements
Restricted cash	603	603
Level I \| Money market funds
Fair value measurements
Financial assets	94,600	76,600
Overnight repurchase agreements \| Level II
Fair value measurements
Cash and and cash equivalents, fair value	$ 100,000	$ 0

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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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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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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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