Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 1,182	$ 4,162
Short-term investments	12,441	18,428
Accounts receivable	1,118	1,022
Inventory	10,890	8,132
Prepaid expenses and other current assets	1,129	1,018
Total current assets	26,760	32,762
Property and equipment, net	4,390	4,435
Other assets	129	129
Total assets	31,279	37,326
LIABILITIES AND STOCKHOLDERS' EQUITY
Current portion of long-term debt, net of discount
Accounts payable	4,036	3,345
Accrued expenses	1,899	2,521
Total current liabilities	5,935	5,866
Long-term debt, less current portion, net of discount	14,748	14,624
Total liabilities	20,683	20,490
Commitments and Contingencies (Note 8)
Stockholders' equity
Preferred stock, $0.001 par value; 10,000,000 authorized; no shares issued and outstanding at March 31, 2018 and December 31, 2017	0	0
Additional paid-in capital	112,258	112,045
Accumulated other comprehensive income		6
Accumulated deficit	(101,758)	(95,311)
Total stockholders' equity	10,596	16,836
Total liabilities and stockholders' equity	31,279	37,326
Common Class A [Member]
Stockholders' equity
Common stock	96	96
Common Class B [Member]
Stockholders' equity
Common stock	$ 0	$ 0