Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (4,216)	$ (5,190)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	81	67
Gain on disposal of equipment	(3)
Net amortization of investment premium and discount	(36)	76
Stock-based compensation	371	221
Accretion of debt discount	49	48
Changes in operating assets and liabilities:
Accounts receivable	65	119
Unbilled revenue	72	(24)
Inventories	62	14
Prepaid expenses and other current assets	(404)	(641)
Other noncurrent assets	(423)	(152)
Accounts payable and accrued expenses	(176)	414
Amounts due to related parties	(10)	(7)
Unearned revenue	38	200
Net cash used in operating activities	(4,530)	(4,855)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of property and equipment	4
Purchases of property and equipment	(57)	(137)
Purchases of investments	(4,582)
Proceeds from sales and maturities of investments	14,695	10,465
Net cash provided by investing activities	10,060	10,328
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of debt issuance costs		(45)
Proceeds from exercise of stock options and ESPP purchases	16	139
Net cash provided by financing activities	16	94
Net increase in cash and cash equivalents	5,546	5,567
Cash and cash equivalents — beginning of period	2,013	23,973
Cash and cash equivalents — end of period	7,559	29,540
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for interest	288	193
Cash paid for income taxes		1
NONCASH INVESTING AND FINANCING ACTIVITIES:
Exchange of membership interest in unconsolidated entity for common stock	2
Purchases of property and equipment included in accounts payable and accrued expenses	$ 2	$ 1