Grant Revenues - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jun. 01, 2014	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant revenues		$ 2,378,000	$ 1,479,000	$ 3,888,000	$ 2,462,000
Type of revenue [extensible list]		us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Outstanding grant receivable		$ 4,281,000		$ 4,281,000		$ 3,078,000
Deferred revenue		$ 0		$ 0		$ 20,000
CPRIT
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant contract term	4 years
Grant contract beginning date	Jun. 01, 2014
Grant contract expiration date	May 31, 2018
CPRIT | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research grant contract amount	$ 19,800,000