CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net loss	$ (15,307)	$ (29,244)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	3,637	3,394
Stock-based compensation	11,813	8,013
Non-cash restructuring benefit		(454)
Accretion of discount or amortization of premium on short-term investments	(464)	(247)
Amortization of debt issuance costs	51	57
Changes in operating assets and liabilities:
Accounts receivable	(6,341)	2,656
Inventory	8,451	(2,112)
Prepaid expenses and other assets	(222)	391
Deferred revenue	114	(288)
Deferred rent		(176)
Accounts payable	1,508	(774)
Accrued compensation and employee related benefits	(2,440)	(720)
Operating lease right-of-use assets	1,505
Operating lease liabilities	(2,255)
Accrued liabilities and other liabilities	164	1,223
Restructuring liabilities		1,576
Net cash provided by (used in) operating activities	214	(16,705)
Investing activities:
Purchases of investments	(59,036)	(33,397)
Proceeds from maturities of investments	51,794	35,402
Purchases of property and equipment	(971)	(3,051)
Net cash used in investing activities	(8,213)	(1,046)
Financing activities:
Principal payments on finance lease obligations	(410)	(717)
Payments on term and equipment loans	(4,222)	(2,230)
Proceeds from term loans, net of debt issuance costs	3,991	16,379
Proceeds from exercise of stock options and employee stock purchase plan	8,041	2,627
Net cash provided by financing activities	7,400	16,059
Net decrease in cash and cash equivalents	(599)	(1,692)
Cash and cash equivalents
Beginning of period	17,530	19,285
End of period	16,931	17,593
Supplemental cash flow information:
Purchases of property and equipment not yet paid	$ 105	$ 3,464