Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	June Offering [Member]	June Purchase Agreement [Member]	Common Stock [Member]	Common Stock [Member] Securities Purchase Agreement [Member]	Common Stock [Member] June Purchase Agreement [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] June Offering [Member]	Additional Paid-In Capital [Member] Securities Purchase Agreement [Member]	Additional Paid-In Capital [Member] June Purchase Agreement [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive (Loss) [Member]
Stockholders Equity, Beginning Balance at Dec. 31, 2017	$ 8,007			$ 42			$ 175,223				$ (167,257)	$ (1)
Stockholders Equity, Beginning Balance, Shares at Dec. 31, 2017				2,134,153
Impact of adoption of Topic 606 | Topic 606 [Member]	2,371										2,371
Issuance of shares related to employee stock option exercises	963						963
Issuance of shares related to employee stock option exercises, Shares				44,354
Issuance of shares related to employee stock purchase plan	6						6
Issuance of shares related to employee stock purchase plan, Shares				1,122
Issuance of shares			$ 4,978		$ 1	$ 2			$ (1)	$ 4,976
Issuance of shares, Shares					1,201,634	1,392,345
Issuance of placement agent warrants	526	$ 427					526	$ 427
Common stock adjustment feature	8,378						8,378
Offering costs related to June Offering			$ (912)							$ (912)
Stock-based compensation	1,550						1,550
Issuance of shares related to reverse stock split, Shares				1,311
Other comprehensive income	1											$ 1
Net loss	(13,480)										(13,480)
Stockholders Equity, Ending Balance at Dec. 31, 2018	12,815			$ 45			191,136				(178,366)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2018				4,774,919
Issuance of shares related to employee stock purchase plan	8						8
Issuance of shares related to employee stock purchase plan, Shares				2,500
Stock-based compensation	422						422
Net loss	(12,612)										(12,612)
Stockholders Equity, Ending Balance at Mar. 31, 2019	$ 633			$ 45			$ 191,566				$ (190,978)
Stockholders Equity, Ending Balance, Shares at Mar. 31, 2019				4,777,419