Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Oct. 31, 2017	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies [Line Items]
Security deposit of lease agreement			$ 47,000
Rent expense			$ 350,000	$ 151,000	$ 140,000
University Research Agreement
Commitments and Contingencies [Line Items]
Research agreement expiration date			Aug. 31, 2018
Payments pursuant to research agreements	$ 188,000		$ 563,000	832,000	$ 563,000
Austin, TX
Commitments and Contingencies [Line Items]
Operating lease agreement, commencement date		2018-01	2015-01
Operating lease agreement, amended date			2016-09
Operating lease agreement, expiration date		Dec. 31, 2019	Dec. 31, 2020
Tenant improvements allowances on both the original space and expansion space				$ 200,000
Sublease agreement date		2017-02
Operating lease agreement, expiration date		2017-12
Operating lease agreement new lease sign date		2017-10