Cash and Cash Equivalents - Narrative (Details)	Jun. 30, 2020 USD ($) patient	Dec. 31, 2019 USD ($)
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 245,735,000	$ 125,699,000
Cash	3,400,000	3,200,000
Investments in money market funds, U.S. Treasury securities and certain short-term investment-grade corporate debt securities with original maturities of 90 days or less	242,400,000	122,500,000
Available for sale securities	$ 0	$ 0
GATHER2 Trial
Cash and Cash Equivalents [Line Items]
Number of patients planned to enroll in trial \| patient	400

Number Of Patients Planned To Enroll In Trial

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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