Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (15,230)	$ (17,450)	$ (16,225)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	941	665	671
Amortization and abandonment of patent and trademark rights	$ 249	477	196
Redeemable warrants valuation adjustment		(14)	(281)
Equity-based compensation	$ 181	326	376
Other-than-temporary impairment of marketable securities	315	145	800
Unrealized gain on securities	$ 63	$ (46)	(71)
Inventory reserve			$ 453
Changes in assets and liabilities:
Inventories	$ (1,326)
Prepaid expenses and other assets	64	$ (41)	$ (36)
Accounts payable	(196)	869	(617)
Accrued expenses	(1,114)	1,105	(2,167)
Net cash used in operating activities	(16,053)	(13,964)	(16,901)
Cash flows from investing activities:
Purchases of property, equipment and construction in progress	(240)	(504)	(898)
Additions to patent and trademark rights	$ (250)	$ (258)	(242)
Office rental deposit			$ (71)
Deposits on capital leases refunded		$ 2
Sales and maturities of short-term and long-term marketable securities	$ 6,842	$ 3,294	$ 23,550
Purchase of short-term and long-term marketable securities
Net cash provided by investing activities	$ 6,352	$ 2,534	$ 22,339
Cash flows provided by (used in) financing activities:
Proceeds from sale of common stock, net of issuance costs	9,681	12,817	249
Payments on capital leases	$ (21)	$ (34)	(45)
Payments on Margin Account Loan			(7,051)
Net cash provided by (used in) financing activities	$ 9,660	$ 12,783	(6,847)
Net (decrease) increase in cash and cash equivalents	(41)	1,353	(1,409)
Cash and cash equivalents at beginning of year	2,156	803	2,212
Cash and cash equivalents at end of year	2,115	2,156	803
Supplemental disclosures of non-cash investing and financing cash flow information:
Issuance of common stock for accounts payable and accrued expenses	672	59	269
Unrealized gain (loss) on marketable securities	$ 63	$ (46)	(71)
Supplemental disclosure of cash flow information:
Capitalized construction interest			143
Cash paid for interest expense	$ 3	$ 11	$ 16