Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (19,202)	$ (18,852)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	928	814
Stock-based compensation expense	2,945	2,267
Amortization of premium on short-term investments	66	89
Interest accrued on long-term debt	44	42
Conversion of accrued interest to long-term debt	370	359
Provision for bad debts	207	0
Changes in operating assets and liabilities:
Accounts receivable	3,056	5,466
Inventory	817	(837)
Prepaid expenses and other	(1,018)	(193)
Other assets	105	(82)
Accounts payable	716	(2,103)
Accrued liabilities	(1,804)	(199)
Accrued compensation and other employee benefits	(2,792)	(3,401)
Customer deposits	(2,190)	218
Deferred revenue	178	(244)
Deferred rent and other liabilities	(124)	1,390
Net cash used in operating activities	(17,698)	(15,266)
Investing activities
Purchases of property and equipment	(1,106)	(2,493)
Proceeds from sale of short-term investments	2,700	1,000
Proceeds from maturity of short-term investments	9,780	10,775
Purchases of short-term investments	(6,000)	(10,125)
Net cash provided by (used in) investing activities	5,374	(843)
Financing activities
Repayment of lease financing obligations	0	(32)
Proceeds from issuance of common stock warrants	748	0
Deferred financing costs	(152)	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	411	288
Net cash provided by financing activities	1,666	934
Net decrease in cash and cash equivalents	(10,658)	(15,175)
Effect of exchange rate changes on cash and cash equivalents and restricted cash	28	8
Cash and cash equivalents and restricted cash
Beginning of period	26,279	20,726
End of period	15,649	5,559
Cash and cash equivalents	26,136
Restricted cash	$ 0	$ 143