The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Organization - Narrative (Details) $ in Thousands	3 Months Ended						9 Months Ended
Organization - Narrative (Details) $ in Thousands	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of reportable segments \| segment							1
Accumulated deficit	$ 388,180						$ 388,180		$ 369,014
Net income (loss)	3,470	$ (19,792)	$ (2,844)	$ (1,069)	$ (4,651)	$ (7,659)	(19,166)	$ (13,379)
Cash and cash equivalents	36,905						36,905		18,286
Short-term investments	$ 37,760						$ 37,760		$ 64,638