Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating Activities
Net loss	$ (8,685)	$ (10,004)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,194	1,641
Amortization of premium on investment securities	364
Gain on investments	(84)
Impairment of assets	20
Stock based compensation	2,396	1,147
(Gain)/loss from changes in fair value of warrants	(510)	963
Loss from change in fair value of long term debt		1,800
Provision for doubtful accounts	234	91
Changes in operating assets and liabilities
Accounts receivable	(478)	463
Inventory	1,404	(1,780)
Prepaid expenses and other current assets	1,410	(1,304)
Restricted cash	(79)	(34)
Other assets	(561)	(221)
Accounts payable	1,825	5,718
Accrued compensation	347	(435)
Other accrued liabilities	1,603	(455)
Deferred revenue	71	(81)
Net cash provided by (used in) operating activities	471	(2,491)
Investing Activities
Purchases of investments	(14,079)
Proceeds from sale of investments	10,599
Proceeds from maturity of investments	10,000
Proceeds from sale of property and equipment	225
Purchases of property and equipment, net	(3,484)	(3,749)
Net cash provided by (used in) investing activities	3,261	(3,749)
Financing Activities
Proceeds from issuance of common stock, net of issuance costs		106
Proceeds from exercise of stock options	1,306
Proceeds from issuance of preferred stock, net		(27)
Costs paid for loan		(6)
Repayments of equipment financing		(585)
Deferred offering costs		(76)
Net cash provided by (used in) financing activities	1,306	(588)
Net increase (decrease) in cash	5,038	(6,828)
Cash at beginning of period	28,947	87,176
Cash at end of period	$ 33,985	$ 80,348