Organization and Description of Business (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended
	Mar. 04, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Nature of Operations
Product revenue			$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Accumulated deficit			(241,551)				(221,772)				(241,551)	$ (221,772)
Cash and cash equivalents			$ 7,851				$ 35,952				$ 7,851	35,952
Proceeds from the issuance of common stock, net												$ 18,535	$ 37,528
Private Placement | Subsequent Event
Nature of Operations
Proceeds from the issuance of common stock, net	$ 7,800	$ 7,800