Liquidity and Ability to Continue as a Going Concern (Details) - USD ($)					1 Months Ended	3 Months Ended	6 Months Ended	10 Months Ended
	Nov. 16, 2018	Jun. 11, 2018	Apr. 26, 2018	Jan. 07, 2018	Aug. 07, 2019	Jun. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jul. 26, 2019	May 16, 2019	Dec. 31, 2018	Jun. 30, 2018	Jan. 26, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Cash and cash equivalents						$ 27,259,000	$ 27,259,000				$ 47,758,000	$ 33,044,000		$ 25,961,000
Restricted cash						500,000	500,000
Accumulated deficit						(548,574,000)	(548,574,000)				$ (519,871,000)
Cash and cash equivalents minimum covenant requirement						$ 2,000,000	$ 2,000,000
Stock issued during period (shares)			685,000
Aggregate net proceeds			$ 21,800,000
Underwriting discounts and commissions	$ 32,500,000
Underwriting discounts and commissions	2,700,000		1,800,000
Offering costs	800,000		$ 400,000
Series A warrants
Class of Stock [Line Items]
Underwriting discounts and commissions	$ 32,500,000
Warrants issued, shares	3,750,000
Warrants issued in conjunction with public share offering (usd per share)	$ 12.00
Term of year from the date of issuance	5 years
Estimated revenue before fees	$ 45,000,000
Warrants exercised (shares)							0
Series B warrants
Class of Stock [Line Items]
Warrants issued, shares	3,750,000
Warrants issued in conjunction with public share offering (usd per share)	$ 9.60
Estimated revenue before fees	$ 36,000,000
Warrants exercised (shares)							2,096
FBR | ATM Agreement
Class of Stock [Line Items]
Commitment to purchase shares													$ 10,300,000
Stock issued during period (shares)						879,859	988,976
Average price paid (usd per share)						$ 4.49	$ 4.83
Aggregate net proceeds						$ 3,800,000	$ 4,600,000
FBR | ATM Agreement | Subsequent event
Class of Stock [Line Items]
Commitment to purchase shares					$ 800,000
Stock issued during period (shares)					1,169,415
Average price paid (usd per share)					$ 3.99
Aggregate net proceeds					$ 4,500,000
Aspire Capital
Class of Stock [Line Items]
Aggregate net proceeds				$ 1,800,000
Minimum price per share (usd per share)										$ 1
Aspire Capital | Second Purchase Agreement
Class of Stock [Line Items]
Commitment to purchase shares		$ 21,000,000				$ 19,700,000	$ 19,700,000			$ 21,000,000
Stock issued during period (shares)		39,578						60,271
Purchase notice (shares)		7,500
Aspire Capital | Second Purchase Agreement | Subsequent event
Class of Stock [Line Items]
Commitment to purchase shares									$ 4,000,000