Supplementary Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected quarterly financial data
License and collaboration revenue - related party	$ 2,719	$ 4,141		$ 1,560	$ 2,353	$ 6,117	$ 11,674	$ 10,781
License and collaboration revenue - related party (reduction)			$ (8,189)
Loss from operations	(17,299)	(17,167)	(31,407)	(14,648)	(15,412)	(9,389)	(9,239)	(8,229)	$ (80,521)	$ (42,269)	$ (37,897)
Net loss	$ (17,501)	$ (16,409)	$ (29,174)	$ (14,103)	$ (13,865)	$ (8,735)	$ (8,663)	$ (7,661)	$ (77,187)	$ (38,924)	$ (36,957)
Net loss per share of common stock, basic and diluted	$ (0.63)	$ (0.61)	$ (1.18)	$ (0.58)	$ (0.57)	$ (0.38)	$ (0.41)	$ (0.36)	$ (2.98)	$ (1.74)	$ (2.09)

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from contract modification which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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