Summary of Significant Accounting Policies - Additional Information (Details)		12 Months Ended
	Jun. 01, 2014 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 01, 2015 Subsidary
Summary Of Significant Accounting Policies [Line Items]
Marketable Securities, Realized Gain (Loss)		$ 0	$ 0	$ 0
Impairments of long-lived assets		$ 0	$ 0	$ 0
Number of subsidiary corporations owned | Subsidary					7
CPRIT | Maximum
Summary Of Significant Accounting Policies [Line Items]
Research grant contract amount	$ 19,800,000