CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (10,668,000)	$ (32,048,000)	$ (31,483,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	747,000	998,000	607,000
Stock-based compensation	719,000	2,155,000	3,650,000
Amortization of intangible assets	112,000	111,000	321,000
Impairment of goodwill		9,858,000
Amortization of debt issuance costs	45,000	37,000
Accrued interest	898,000	650,000
(Gain) loss on disposal of assets	(12,000)	4,000
Changes in assets and liabilities:
Accounts receivable	(1,122,000)	170,000	(552,000)
Inventories	(315,000)	146,000	(716,000)
Prepaid expenses and other assets	(1,016,000)	459,000	104,000
Accounts payable	(402,000)	(419,000)	261,000
Deferred revenue and other liabilities	3,435,000	(64,000)	334,000
Net cash used in operating activities	(7,579,000)	(17,943,000)	(27,474,000)
Cash flows from investing activities:
Purchases of property and equipment	(300,000)	(646,000)	(1,202,000)
Net proceeds from sale of assets	12,000
Proceeds from sales and maturities of marketable securities	2,604,000	50,486,000	44,953,000
Purchases of marketable securities	(1,602,000)	(36,874,000)	(36,873,000)
Net cash provided by investing activities	714,000	12,966,000	6,878,000
Cash flows from financing activities:
Proceeds from sale of common stock, net of issuance costs	1,967,000	364,000	23,140,000
Proceeds from the issuance of notes payable, net of issuance costs		7,877,000
Payments on capital lease obligations		(138,000)	(14,000)
Net cash provided by financing activities	1,967,000	8,103,000	23,126,000
Net increase (decrease) in cash and cash equivalents	(4,898,000)	3,126,000	2,530,000
Cash and cash equivalents at beginning of period	8,766,000	5,640,000
Cash and cash equivalents at end of period	3,868,000	8,766,000	5,640,000
Supplemental disclosure:
Issuance of convertible notes in settlement of accrued interest	854,000	336,000
Cash paid for income taxes	$ 2,000	$ 21,000	$ 56,000