CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net loss	$ (29,244)	$ (7,988)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	3,394	2,868
Stock-based compensation	8,013	4,763
Non-cash restructuring benefit	(454)
Accretion of discount or amortization of premium on short-term investments	(247)	120
Amortization of debt issuance costs	57	72
Changes in operating assets and liabilities:
Accounts receivable	2,656	(8,138)
Inventory	(2,112)	(18,083)
Prepaid expenses and other assets	391	278
Deferred revenue	(288)	(170)
Deferred rent	(176)	977
Accounts payable	(774)	(4,125)
Accrued compensation and benefits	(720)	(3,745)
Accrued liabilities	1,223	117
Accrued restructuring costs	1,576
Net cash used in operating activities	(16,705)	(33,054)
Investing activities:
Purchases of investments	(33,397)	(28,887)
Proceeds from maturities of investments	35,402	50,726
Purchases of property and equipment	(3,051)	(6,156)
Net cash provided by (used in) investing activities	(1,046)	15,683
Financing activities:
Payments on capital lease financing obligations	(717)	(847)
Payments on term loans	(2,230)	(1,730)
Proceeds from term loans, net of debt issuance costs	16,379
Proceeds from exercise of stock options and employee stock purchase plan	2,627	4,520
Payments of deferred offering costs		(650)
Net cash provided by financing activities	16,059	1,293
Net decrease in cash and cash equivalents	(1,692)	(16,078)
Cash and cash equivalents
Beginning of period	19,285	33,636
End of period	17,593	17,558
Supplemental disclosure of non-cash financing and investing activities:
Purchases of property and equipment not yet paid	$ 3,464	$ 502