Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	$ 1	$ 194,016	$ (183,907)	$ 10,110
Beginning Balance, (in shares) at Dec. 31, 2017	1,370,992
Share-based compensation expense		306		306
Issuance of common stock in public offerings		2,682		2,682
Issuance of stock in public offerings (in shares)	190,664
Issuance of common stock under ESPP		3		3
Issuance of common stock under ESPP (in shares)	188
Issuance of common stock to 401(k) plan		6		6
Issuance of common stock to 401(k) plan (in shares)	440
Net loss			(4,784)	(4,784)
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2018	$ 1	197,013	(188,691)	8,323
Ending Balance, (in shares) at Mar. 31, 2018	1,562,284
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	$ 1	194,016	(183,907)	10,110
Beginning Balance, (in shares) at Dec. 31, 2017	1,370,992
Issuance of common stock upon vesting of restricted stock units (in shares)	4,250
Issuance of common stock under ESPP (in shares)	1,133
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2018	$ 1	223,440	(207,330)	$ 16,111
Ending Balance, (in shares) at Dec. 31, 2018	9,309,255			9,309,255
Share-based compensation expense		67		$ 67
Issuance of common stock upon vesting of restricted stock units (in shares)	750
Issuance of common stock under ESPP		1		1
Issuance of common stock under ESPP (in shares)	1,065
Net loss			(2,635)	(2,635)
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2019	$ 1	$ 223,508	$ (209,965)	$ 13,544
Ending Balance, (in shares) at Mar. 31, 2019	9,311,070			9,311,070