Balance Sheet Details - Summary of Prepaid Expenses and Other Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Prepaid manufacturing and process development costs	$ 2,446	$ 175
Prepaid insurance	616	1,171
Interest receivable	298	265
Prepaid clinical trial costs	82
Other prepaids and current assets (including related party amounts of $0 and $28, respectively)	112	77
Prepaid expenses and other current assets	$ 3,554	$ 1,688

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 10
-Section 05
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68074540&loc=d3e5865-108316

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section 45
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6787-107765

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 10
-Section 05
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-URI http://asc.fasb.org/extlink&oid=68074540&loc=d3e5879-108316

Name:	us-gaap_PrepaidInsurance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant