Organization (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	Jan. 31, 2017	Nov. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2016	Jul. 26, 2016	Jun. 08, 2016	Dec. 31, 2014
Stock issued, shares	6,250,000
Stock issued, price per share	$ 12.00
Proceeds from IPO, net	$ 66,000							$ 69,750
Offering expenses	3,700
Underwriting discounts and commissions	$ 5,300
Transaction costs								$ 3,293	$ 445
Gross proceeds from common stock							$ 95,954
Shares outstanding	45,078,666						78,643,954	45,078,666
Common stock, shares authorized							200,000,000	200,000,000			200,000,000
Common stock, par value							$ 0.001	$ 0.001			$ 0.001
Accumulated deficit							$ (237,397)	$ (155,705)
Working capital							13,400
Proceeds from issuance of redeemable convertible units								5,500	10,833
Cash and cash equivalents							$ 67,517	$ 36,093	$ 21,498				$ 20,991
Class E Redeemable Convertible Units [Member]
Stock issued, shares								478,266
Proceeds from issuance of redeemable convertible units								$ 5,500
Convertible Preferred Stock [Member]
Preferred stock, shares authorized							10,000,000	10,000,000			10,000,000	10,000,000
Preferred stock, par value							$ 0.001	$ 0.001			$ 0.001
License Agreement, Jinghua [Member]
Milestone payment					$ 2,000		$ 2,000	$ 2,000
Proceeds from issuance of redeemable convertible units						$ 10,000
2015 Second-Lien Convertible Debt [Member]
Shares converted	19,034,467
2015 Credit Agreement [Member]
Deferred Principal Payments				$ 380						$ 380
Additional equity capital to be raised				$ 17,000						$ 40,000
2017 Public Offering [Member]
Stock issued, shares		4,500,000	22,275,000				26,775,000
Transaction costs							$ 5,300
Gross proceeds from common stock		$ 13,600	$ 66,800				80,400
Net proceeds from common stock							$ 75,100
2017 Private Placement [Member]
Stock issued, shares				6,767,855			6,767,855
Transaction costs				$ 1,800			$ 1,800
Gross proceeds from common stock				22,700			22,700
Net proceeds from common stock				$ 20,900			$ 20,900