Going Concern (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Aug. 01, 2016	Oct. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Going Concern [Line Items]
Working capital (deficit)					$ 13,400
Accumulated deficit					(237,397)	$ (155,705)
Net cash used in operating activities					(64,098)	(52,950)	$ (60,977)
Gross proceeds from common stock					95,954
Transaction costs						$ 3,293	$ 445
Stock issued, shares	6,250,000
Price per share of common stock	$ 12.00
2017 Public Offering [Member]
Going Concern [Line Items]
Gross proceeds from common stock		$ 13,600	$ 66,800		80,400
Net proceeds from common stock					75,100
Transaction costs					$ 5,300
Stock issued, shares		4,500,000	22,275,000		26,775,000
Price per share of common stock					$ 3.001
Warrants issued		1,800,000	8,910,000		10,710,000
Warrants exercise price					$ 3.35
Warrant exercise price term					5 years
2017 Private Placement [Member]
Going Concern [Line Items]
Gross proceeds from common stock				$ 22,700	$ 22,700
Net proceeds from common stock				20,900	20,900
Transaction costs				$ 1,800	$ 1,800
Stock issued, shares				6,767,855	6,767,855
Price per share of common stock				$ 3.36	$ 3.36
Warrants issued				2,707,138	2,707,138
Warrants exercise price				$ 4.50	$ 4.50
Warrant exercise price term				13 months	13 months