Balance Sheet Components - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid research and development expenses	$ 6,643	$ 946
Collaboration accounts receivable	7,364	0
Prepaid insurance	0	927
Accrued interest on short-term marketable securities	1,182	464
Other prepaid and current assets	1,350	1,044
Total prepaid expenses and other current assets	$ 16,539	$ 3,381

Collaboration Accounts Receivable

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- Definition

Prepaid Research And Development Expense, Current

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- Definition

Carrying amount as of the balance sheet date of current interest earned but not received. Also called accrued interest or accrued interest receivable. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

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Amount of asset related to consideration paid in advance for other costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

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- Definition

Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer.

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Amount of asset related to consideration paid in advance for insurance that provides economic benefits within a future period of one year or the normal operating cycle, if longer.

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