Net Loss Per Share - Computation of Net (Loss) Income Per Share (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
Earnings Per Share [Abstract]
Net loss	$ (40,200)	$ (26,557)	$ (28,783)	$ (39,846)	$ (53,117)	$ (69,209)	$ 14,863	$ (19,243)	$ (112,689)	$ (120,741)	$ (92,189)
Weighted average shares-basic and diluted (shares)									110,585,768	103,305,911	85,115,592
Net loss per share - basic and diluted (in dollar per share)	$ (0.36)	$ (0.24)	$ (0.26)	$ (0.36)	$ (0.52)	$ (0.66)	$ 0.14	$ (0.19)	$ (1.02)	$ (1.17)	$ (1.08)