Amount of cash and cash equivalents restricted as to withdrawal or usage. 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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Nature of the Business and Basis of Presentation - Liquidity (Details) - USD ($)	Jun. 11, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit		$ 379,454,000	$ 335,753,000
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents, and restricted cash		61,387,000	$ 91,551,000	$ 30,479,000	$ 37,682,000
Restricted cash and cash equivalents		1,700,000
Collaborative Arrangement
Cash and Cash Equivalents [Line Items]
Upfront cash payment	$ 75,000,000
SOBI Purchase Agreement
Cash and Cash Equivalents [Line Items]
Sale common stock	$ 25,000,000
Russian subsidiary \| Unrestricted cash
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents, and restricted cash		$ 300,000