Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Accumulated deficit			$ (500,654)	$ (470,111)	$ 1,300
Working capital			52,200
Cash and cash equivalents			$ 60,541	65,134
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	true
Lessee, operating lease, existence of option to extend		true	true
Impairments of right-of-use assets	$ 2,400	$ 2,400
leasehold improvement assets	$ 500	$ 500			$ 2,200
Loss on impairment of long-lived assets			$ 5,784
Estimated useful life of intangible assets			9 months 18 days
Unbilled receivable				1,604
ASU 2018-18 [Member]
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]			true
Change in Accounting Principle, Accounting Standards Update, Early Adoption [true false]			true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]			true
Change in Accounting Principle, Accounting Standards Update, Adoption Date			Jan. 01, 2020
Grant Revenue [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
Assembled Workforce [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets			3 years
Discounted Cash Flows [Member]
Significant Accounting Policies [Line Items]
Right-of-use and leasehold improvement assets, discount rate	0.095	0.095
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