Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (12,747)	$ (13,916)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	215	227
Gain on disposal of equipment	(3)
Net amortization of investment premium and discount	(82)	115
Loss on sale of investments	2
Stock-based compensation	1,177	661
Accretion of debt discount	98	148
Loss on extinguishment of debt	900
Changes in operating assets and liabilities:
Accounts receivable	276	609
Unbilled revenue	123	(62)
Inventories	164	(32)
Prepaid expenses and other current assets	(222)	(492)
Other noncurrent assets	(245)	4
Accounts payable and accrued expenses	(496)	237
Amounts due to related parties	1
Unearned revenue	(443)	(277)
Net cash used in operating activities	(11,282)	(12,778)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of property and equipment	4
Purchases of property and equipment	(77)	(222)
Purchases of investments	(19,405)	(21,129)
Proceeds from sales and maturities of investments	57,778	20,247
Net cash provided by (used in) investing activities	38,300	(1,104)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of debt issuance costs		(46)
Payments of debt extinguishment costs	(1,125)
Payments on notes payable	(25,000)
Proceeds from exercise of stock options and ESPP purchases	24	428
Net cash (used in) provided by financing activities	(26,101)	382
Net increase (decrease) in cash and cash equivalents	917	(13,500)
Cash and cash equivalents — beginning of period	2,013	23,973
Cash and cash equivalents — end of period	2,930	10,473
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for interest	746	755
Cash paid for income taxes	2	2
NONCASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment included in accounts payable and accrued expenses	2
Exchange of membership interest in unconsolidated entity for common stock	$ 2
Stock option exercise cost included in accounts receivable		$ 6