Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net loss	$ (39,803)	$ (23,407)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,017	1,661
Stock-based compensation expense	5,848	5,109
Amortization of premium on short-term investments	36	78
Interest accrued on long-term debt	88	85
Conversion of accrued interest to long-term debt	747	724
Provision for bad debts	445	201
Inventory Write-down	45	0
Changes in operating assets and liabilities:
Accounts receivable	1,727	3,515
Inventory	1,636	(2,472)
Prepaid expenses and other	(1,207)	(1,506)
Other assets	(2)	(87)
Accounts payable	1,127	(392)
Accrued liabilities	(501)	1,017
Accrued compensation and other employee benefits	(621)	(1,669)
Customer deposits	557	164
Deferred revenue	(145)	(13,307)
Deferred rent and other liabilities	(254)	1,320
Net cash used in operating activities	(28,260)	(28,966)
Investing activities
Purchases of property and equipment	(1,732)	(3,384)
Proceeds from sale of short-term investments	5,410	1,000
Proceeds from maturity of short-term investments	25,600	28,474
Purchases of short-term investments	(6,000)	(34,785)
Net cash provided by (used in) investing activities	23,278	(8,695)
Financing activities
Repayment of lease financing obligations	0	(58)
Proceeds from sale of common stock, net	0	56,486
Proceeds from issuance of common stock warrants	1,423	0
Deferred financing costs	(63)	0
Tax withholdings related to net share settlements of restricted stock units	(108)	(248)
Proceeds from issuance of common stock for employee stock purchase plan	767	926
Proceeds from exercise of stock options	994	601
Net cash provided by financing activities	3,013	57,707
Net (decrease) increase in cash, cash equivalents and restricted cash	(1,969)	20,046
Effect of exchange rate changes on cash and cash equivalents and restricted cash	(24)	18
Cash and cash equivalents and restricted cash
Beginning of period	26,279	20,726
End of period	24,286	40,790
Cash and cash equivalents	26,136
Restricted cash	$ 0	$ 143