Description of the Business and Liquidity (Details) $ in Thousands	1 Months Ended		3 Months Ended					9 Months Ended
	Oct. 31, 2019 USD ($) shares	Oct. 31, 2017 USD ($)	Sep. 30, 2019 USD ($) item	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Capitalization, Equity [Line Items]
Number of dose forms for modulator | item			2					2
Liquidity
Losses			$ 13,806	$ 12,423	$ 12,483	$ 11,110	$ 5,999	$ 38,712	$ 26,614
Cash used for operating activities								32,384	$ 18,684
Accumulated deficit			220,165					220,165		$ 181,453
Cash, cash equivalents and investment balances			$ 39,900					$ 39,900
2017 Equity Distribution Agreement
Liquidity
Term of Equity Distribution Agreement		3 years
Value of common stock authorized under EDA		$ 50,000
Number of common stock shares sold (in shares) | shares	1,290,464
Proceeds from sale of common stock, net	$ 1,700
Remaining value of common stock shares available under EDA	$ 48,200