Strategic Alliance and Collaboration with Servier - Narrative (Details) € in Millions		1 Months Ended	3 Months Ended								12 Months Ended		63 Months Ended
	Mar. 16, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue			$ 476,000	$ 944,000	$ 2,182,000	$ 4,784,000	$ 1,192,000	$ 1,631,000	$ 718,000	$ 462,000	$ 8,386,000	$ 4,003,000
Amounts incurred but not yet billed							1,100,000					1,100,000				$ 500,000
Accounts receivable							1,456,000					1,456,000				24,000
Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential commercialization milestone payments															€ 175.0	200,300,000
Milestone payment earned	$ 3,700,000	$ 3,000,000
Minimum | Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential development milestone payments															5.8	6,600,000
Potential regulatory milestone payments															10.0	11,400,000
Maximum | Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential development milestone payments															13.8	15,800,000
Potential regulatory milestone payments															€ 40.0	45,800,000
Research and development reimbursable costs
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue											3,683,000	3,097,000
License revenue | Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue											0		€ 9.0	$ 12,400,000
Collaboration revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue											$ 7,373,000	3,097,000
Servier
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accounts receivable							$ 1,400,000					$ 1,400,000				$ 0