Legal Proceedings (Details) - USD ($)	1 Months Ended				2 Months Ended	12 Months Ended
	Feb. 28, 2018	Nov. 30, 2017	Oct. 31, 2017	Sep. 30, 2016	May 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 17, 2016
Loss Contingencies [Line Items]
Proceeds from issuance of common stock		$ 86,600,000	$ 86,600,000	$ 30,300,000	$ 75,400,000	$ 86,624,000	$ 30,310,000	$ 75,359,000
Subsequent Event
Loss Contingencies [Line Items]
Escrow disbursements made during the period	$ 750,000
TheraVectys SA | Subsequent Event
Loss Contingencies [Line Items]
Escrow disbursements made during the period	$ 5,250,000
TheraVectys SA
Loss Contingencies [Line Items]
Payments for underwriting expense		$ 1,250,000
Collaborative Arrangement | TheraVectys SA | Maximum
Loss Contingencies [Line Items]
Obligation							1,400,000		$ 1,400,000
Settled Litigation | TheraVectys SA v. Immune Design Corp.
Loss Contingencies [Line Items]
Settlement agreement, escrow deposit									6,000,000
Settlement agreement, additional amount based on future conditions									1,250,000
Settlement agreement, contingent payout based on capital funding									$ 25,000,000
Payment of legal settlement, milestone one, percent									50.00%
Payment of legal settlement, milestone two, percent									50.00%
Estimate of possible loss									$ 7,300,000
Estimated litigation liability									$ 5,900,000
Loss in period							$ 5,900,000