Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (41,935)	$ (39,803)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,377	1,970
Non-cash operating lease cost	1,332	0
Stock-based compensation expense	7,958	5,848
Amortization of premium on short-term investments	236	36
Amortization of deferred financing costs	343	180
Conversion of accrued interest to long-term debt	941	747
Provision for bad debts	38	445
Inventory Write-down	554	45
Changes in operating assets and liabilities:
Accounts receivable	(1,752)	1,727
Inventory	(4,361)	1,636
Prepaid expenses and other assets	(3,488)	(1,317)
Accounts payable	(2,551)	1,127
Accrued liabilities	(200)	(501)
Accrued compensation and other employee benefits	(2,306)	(621)
Customer deposits	(798)	557
Deferred revenue	(4,624)	(145)
Operating lease liabilities	(920)	0
Deferred rent and other liabilities	0	(254)
Net cash used in operating activities	(49,156)	(28,323)
Investing activities
Purchases of property and equipment	(1,147)	(1,732)
Proceeds from sale of short-term investments	0	5,410
Proceeds from maturity of short-term investments	60,120	25,600
Purchases of short-term investments	(102,579)	(6,000)
Net cash (used in) provided by investing activities	(43,606)	23,278
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	0
Proceeds from issuance of common stock warrants	1,306	1,423
Tax withholdings related to net share settlements of restricted stock units	(1,299)	(108)
Proceeds from issuance of common stock for employee stock purchase plan	939	767
Proceeds from exercise of stock options	12,665	994
Net cash provided by financing activities	101,784	3,076
Net increase (decrease) in cash, cash equivalents	9,022	(1,969)
Effect of exchange rate changes on cash and cash equivalents	(7)	(24)
Cash and cash equivalents
Beginning of period	24,356	26,279
End of period	33,371	24,286
Right-of-use assets obtained in exchange for lease obligations	$ 27,880	$ 0