Grant Revenues - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant revenues		$ 1,373	$ 3,427	$ 2,232	$ 3,427
CPRIT
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant contract term	3 years
Grant contract beginning date	Jun. 01, 2014
Grant contract expiration date	May 31, 2017
Outstanding grant receivable		$ 1,600		1,600		$ 1,700
CPRIT | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research grant contract amount	$ 19,800			$ 19,800