Significant Agreements (Details) - USD ($) $ in Thousands			1 Months Ended	6 Months Ended
	Jun. 25, 2018	Apr. 03, 2018	Mar. 31, 2018	Jun. 30, 2018
Significant Agreements
Issuance of stock (in shares)	6,591,800
Non-cash research and development license expense				$ 4,448
Takeda | License agreement
Significant Agreements
Issuance of stock (in shares)		223,544
Non-cash research and development license expense		$ 4,448
One-time non-refundable development milestone payment		70,000
One-time non-refundable non-creditable sales milestone payment		$ 70,000
Period after date of first commercial sale (in years)			10 years