Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (56,290)	$ (34,811)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,975	2,408
Stock-based compensation expense	8,683	8,201
Amortization of premium on short-term investments	373	113
Amortization of deferred financing costs	276	198
Conversion of accrued interest to long-term debt	1,130	1,097
Provision for bad debts	467	361
Inventory Write-down	629	0
Changes in operating assets and liabilities:
Accounts receivable	562	3,552
Inventory	3,468	(5,871)
Prepaid expenses and other assets	(2,355)	(2,412)
Accounts payable	1,261	(1,714)
Accrued liabilities	(1,388)	711
Accrued compensation and other employee benefits	532	(900)
Customer deposits	1,263	8,105
Deferred revenue	(789)	(19,608)
Deferred rent and other liabilities	(384)	1,266
Net cash used in operating activities	(39,587)	(39,304)
Investing activities
Purchases of property and equipment	(2,855)	(3,804)
Proceeds from sale of short-term investments	5,410	2,300
Proceeds from maturity of short-term investments	34,100	38,324
Purchases of short-term investments	(62,150)	(48,305)
Net cash used in investing activities	(25,495)	(11,485)
Financing activities
Repayment of lease financing obligations	0	(58)
Proceeds from sale of common stock, net	53,847	56,486
Proceeds from issuance of common stock warrants	2,266	175
Deferred financing costs	(63)	0
Tax withholdings related to net share settlements of restricted stock units	(197)	(309)
Proceeds from issuance of common stock for employee stock purchase plan	1,451	1,793
Proceeds from exercise of stock options	2,727	892
Net cash provided by financing activities	60,031	58,979
Net (decrease) increase in cash, cash equivalents and restricted cash	(5,051)	8,190
Effect of exchange rate changes on cash and cash equivalents and restricted cash	(29)	24
Cash and cash equivalents and restricted cash
Beginning of period	26,279	20,726
End of period	21,199	28,940
Cash and cash equivalents	26,136
Restricted cash	$ 0	$ 143