Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Accumulated deficit					$ (470,111,000)	$ (450,565,000)
Working capital					63,300,000
Cash and cash equivalents					65,134,000	56,992,000
Cash flows from investing activities						3,168,000
Cash flows from financing activities					$ 25,250,000	1,948,000
Number of operating segment | Segment					1
Cash and cash equivalents, restricted cash maturity period					Three months or less
Lessee, operating lease, existence of option to extend	true				true
Lessee, operating lease, existence of option to terminate					true
Impairments of right-of-use assets					$ 0
Impairments of long-lived assets					$ 0	0
Estimated useful life of intangible assets					1 year 9 months 18 days
Unbilled receivable					$ 1,604,000
Build-to-suit lease asset						8,651,000
Build-to-suit lease obligation						7,324,000
Operating lease ROU assets					8,697,000
Operating lease obligation					10,233,000
Reclassification of restricted cash					(1,328,000)
Grant [Member] | Cancer Prevention & Research Institute of Texas [Member] | Aravive Biologics [Member]
Significant Accounting Policies [Line Items]
Deferred revenue						$ 100,000
Grant [Member] | Cancer Prevention & Research Institute of Texas [Member] | Aravive Biologics [Member] | Prepaid Expenses and Other Current Assets [Member]
Significant Accounting Policies [Line Items]
Unbilled receivable					$ 1,600,000
Assembled Workforce [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets					3 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives					3 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives					5 years
ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease ROU assets							$ 10,400,000
Leasehold improvements							2,200,000
Operating lease obligation							12,600,000
ASU 2016-02 [Member] | Restatement Adjustment [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit							1,300,000
Cash flows from investing activities		$ (1,500,000)	$ (1,900,000)	$ (1,900,000)
Cash flows from financing activities		$ 1,500,000	$ 1,900,000	$ 1,900,000
Deferred rent							(100,000)
ASU 2016-02 [Member] | Restatement Adjustment [Member] | 1020 Marsh Road, Menlo Park, California [Member]
Significant Accounting Policies [Line Items]
Build-to-suit lease asset							(8,600,000)
Build-to-suit lease obligation							$ (7,300,000)
ASU-2016-18 [Member] | Reclassification of Restricted Cash to Cash and Cash Equivalents [Member]
Significant Accounting Policies [Line Items]
Reclassification of restricted cash					$ 2,400,000