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Nature of Business and Overview (Details) $ in Thousands		3 Months Ended								12 Months Ended
Nature of Business and Overview (Details) $ in Thousands	Feb. 08, 2019	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Nature of Business and Overview
Reverse stock split	0.067
Cash, cash equivalents and marketable securities		$ 194,400								$ 194,400
Net loss		(21,900)	$ (14,224)	$ (11,031)	$ (12,625)	$ (10,447)	$ (11,413)	$ (11,779)	$ (17,239)	(59,780)	$ (50,878)	$ (151,184)
Net cash used in operations										(40,404)	(46,415)	$ (75,235)
Gross carrying amount of indefinite-lived		$ 30,700				$ 48,700				$ 30,700	$ 48,700