Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (64,683)	$ (56,290)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,625	2,975
Non-cash operating lease cost	2,069	0
Stock-based compensation expense	12,706	8,683
Amortization of premium on short-term investments	(11)	373
Amortization of deferred financing costs	575	276
Conversion of accrued interest to long-term debt	1,565	1,130
Provision for bad debts	(62)	467
Inventory Write-down	784	629
Changes in operating assets and liabilities:
Accounts receivable	(2,224)	562
Inventory	(7,161)	3,468
Prepaid expenses and other assets	(5,292)	(2,418)
Accounts payable	(2,027)	1,261
Accrued liabilities	1,133	(1,388)
Accrued compensation and other employee benefits	(1,232)	532
Customer deposits	(1,705)	1,263
Deferred revenue	(6,244)	(789)
Operating lease liabilities	(1,701)	0
Deferred rent and other liabilities	0	(384)
Net cash used in operating activities	(69,885)	(39,650)
Investing activities
Purchases of property and equipment	(1,832)	(2,855)
Proceeds from sale of short-term investments	2,500	5,410
Proceeds from maturity of short-term investments	84,070	34,100
Purchases of short-term investments	(122,084)	(62,150)
Net cash used in investing activities	(37,346)	(25,495)
Financing activities
Borrowings under long-term debt agreement	20,000	0
Deferred costs related to long-term debt	100	0
Proceeds from sale of common stock, net	68,273	53,847
Proceeds from issuance of common stock warrants	1,821	2,266
Tax withholdings related to net share settlements of restricted stock units	(1,474)	(197)
Proceeds from issuance of common stock for employee stock purchase plan	1,952	1,451
Proceeds from exercise of stock options	15,899	2,727
Net cash provided by financing activities	106,371	60,094
Net decrease in cash, cash equivalents	(860)	(5,051)
Effect of exchange rate changes on cash and cash equivalents	(54)	(29)
Cash and cash equivalents
Beginning of period	24,356	26,279
End of period	23,442	21,199
Right-of-use assets obtained in exchange for lease obligations	$ 27,364	$ 0