CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (7,068)	$ (14,442)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,155	1,120
Stock-based compensation	3,477	2,065
Non-cash restructuring benefit		454
Accretion of discount or amortization of premium on short-term investments	(197)	(60)
Amortization of debt issuance costs	18	21
Changes in operating assets and liabilities:
Accounts receivable	504	5,221
Inventory	3,506	(7,623)
Prepaid expenses and other assets	423	561
Deferred revenue	167	(473)
Deferred rent		(1,123)
Accounts payable	949	34
Accrued compensation and employee related benefits	(3,279)	(1,236)
Operating lease right-of-use assets	419
Operating lease liabilities	(739)
Accrued liabilities and other liabilities	(66)	307
Restructuring liabilities		3,638
Net cash used in operating activities	(731)	(11,536)
Investing activities:
Purchases of investments	(22,222)	(8,857)
Proceeds from maturities of investments	22,944	17,850
Purchases of property and equipment	(305)	(698)
Net cash provided by investing activities	417	8,295
Financing activities:
Principal payments on finance lease obligations	(147)	(242)
Payments on term loans	(250)	(2,147)
Proceeds from term loans, net of debt issuance costs		12,379
Proceeds from exercise of stock options and employee stock purchase plan	1,842	1,966
Net cash provided by financing activities	1,445	11,956
Net increase in cash and cash equivalents	1,131	8,715
Cash and cash equivalents
Beginning of period	17,530	19,285
End of period	18,661	28,000
Supplemental disclosure of non-cash financing and investing activities:
Purchases of property and equipment not yet paid	$ 347	$ 281