CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Activities
Net loss	$ (14,867)	$ (22,992)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	1,830	1,438
Provision for expected credit losses	862	342
Provision (benefit) for inventory obsolescence	(363)	679
Change in fair value of common stock warrants	1,922	12,746
Amortization of discount on short-term investments	(66)	(94)
Stock-based compensation expense	15,865	9,834
Other	19	27
Changes in operating assets and liabilities:
Accounts receivable, net	(8,292)	1,821
Inventories, net	(11,095)	(3,690)
Prepaid and other current assets	(2,231)	(1,036)
Other long-term assets	(383)	(225)
Accounts payable	4,294	4,376
Accrued expenses	(2,124)	(553)
Employee-related liabilities	(6,253)	(6,982)
Deferred revenue	1,524	861
Other current liabilities	431	(2,120)
Other long-term liabilities	(1,704)	1,444
Net cash used in operating activities	(20,631)	(4,124)
Investing Activities
Purchases of short-term investments	(9,727)	(42,914)
Proceeds from maturities of short-term investments	30,859	43,700
Proceeds from sales of short-term investments	18,550	1,400
Purchases of property and equipment	(6,766)	(1,408)
Net cash provided by investing activities	32,916	778
Financing Activities
Proceeds from exercise of common stock warrants	7	64
Proceeds from issuance of common stock under Company stock plans	11,474	1,898
Net cash provided by financing activities	11,481	1,962
Effect of foreign exchange rate changes on cash	(456)	3
Net increase (decrease) in cash and cash equivalents	23,310	(1,381)
Cash and cash equivalents at beginning of period	51,175	41,826
Cash and cash equivalents at end of period	74,485	40,445
Supplemental disclosures of cash flow information
Income taxes paid	91	0
Supplemental schedule of non-cash investing and financing activities
Right-of-use assets obtained in exchange for operating lease obligations	8,805	3,053
Property and equipment included in accounts payable	$ 1,880	$ 130