CIRM Grant (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Apr. 30, 2019
Additional Information of CIRM Grant [Abstract]
Grant award for clinical development support			$ 6.5
Receivable of offset grants against expenses	$ 0.4	$ 1.1

Amount of progress payment offset against unbilled government contract receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 310
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84167097&loc=d3e55549-109407

Name:	us-gaap_GovernmentContractReceivableProgessPaymentsOffset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant