Stockholders' Deficit (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended				6 Months Ended		12 Months Ended
	May 10, 2019 shares	Aug. 02, 2019 USD ($) shares	Apr. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) shares	Mar. 31, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	May 09, 2019 shares	Dec. 31, 2018 USD ($) shares	Jan. 31, 2017 USD ($)
Subsidiary, Sale of Stock [Line Items]
Reverse stock split	20
Common stock, shares authorized | shares	600,000,000			600,000,000				600,000,000				600,000,000
Preferred stock, shares authorized | shares	2,000,000			2,000,000				2,000,000				2,000,000
Common stock, shares outstanding | shares	23,472,574			23,472,574				23,472,574			469,453,883	19,222,410
Proceeds from shares sold | $				$ 3		$ 53,887		$ 55,242	$ 96,486
December 2018 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range | $ / shares					$ 10.57
Shares sold | shares		400,000			1,700,000
Proceeds from shares sold | $		$ 2,300			$ 17,400
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value | $												$ 100,000
Shelf Registration Statement Remaining Unissued Capital | $		$ 79,900
Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range | $ / shares			$ 33.00
Shares sold | shares			1,700,000
Common stock issued upon exercise in full over-allotment granted | shares			200,000
Payments of Stock Issuance Costs | $			$ 54,000
December 2017 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range | $ / shares					$ 15.33		$ 41.86
Shares sold | shares					2,500,000		800,000
Proceeds from shares sold | $					$ 37,900		$ 32,300			$ 75,000
January 2017 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range | $ / shares							$ 30.80
Shares sold | shares							300,000
Proceeds from shares sold | $							$ 10,300
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value | $													$ 75,000