Nature of the Business and Basis of Presentation - Going Concern(Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Going Concern
Net losses	$ (42,915)	$ (28,260)	$ (100,108)	$ (38,065)
Accumulated deficit	175,564		175,564		$ 75,456
Cash	$ 175,754	$ 1,167	$ 175,754	$ 1,167	$ 23,565	$ 1,460