Research Collaboration and License Agreement (Details) - Research Collaboration and License Agreement - USD ($)	3 Months Ended
	Mar. 31, 2018	Oct. 31, 2013
Research Collaboration and License Agreement
Term	10 years
PTG-300 [Member]
Research Collaboration and License Agreement
Upfront payment to the former collaboration partner		$ 250,000
Additional payment obligation to the former collaboration partner		$ 250,000
Potential obligation to former collaboration partner for development and commercialization of product	$ 128,500,000