Selected Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 50,030	$ 29	$ 29	$ 30	$ 29	$ 230	$ 29	$ 30	$ 50,118	$ 318	$ 463
Operating Expenses	58,082	42,344	26,892	27,090	34,870	24,298	17,172	14,921	154,408	91,261	55,703
Loss from operations	(8,052)	(42,315)	(26,863)	(27,060)	(34,841)	(24,068)	(17,143)	(14,891)	(104,290)	(90,943)	(55,240)
Net loss and comprehensive loss	$ (8,074)	$ (42,130)	$ (26,544)	$ (25,932)	$ (34,459)	$ (23,454)	$ (16,375)	$ (14,097)	$ (102,680)	$ (88,385)	$ (53,079)
Basic and diluted loss per Common Share (expressed in $ per share)	$ (0.05)	$ (0.34)	$ (0.24)	$ (0.23)	$ (0.36)	$ (0.25)	$ (0.18)	$ (0.16)	$ (0.87)	$ (0.95)	$ (0.63)