Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net loss	$ (18,852)	$ (14,603)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	814	692
Stock-based compensation expense	2,267	1,927
Amortization of premium on short-term investments	89	70
Interest accrued on long-term debt	42	37
Conversion of accrued interest to long-term debt	359	315
Changes in operating assets and liabilities:
Accounts receivable, net	5,466	4,198
Inventory	(837)	(2,379)
Prepaid expenses and other	(193)	758
Other assets	(82)	0
Accounts payable	(2,103)	270
Accrued liabilities	(3,382)	(4,610)
Deferred revenue	(244)	20,002
Deferred rent and other liabilities	1,390	904
Net cash (used in) provided by operating activities	(15,266)	7,581
Investing activities
Purchases of property and equipment	(2,493)	(828)
Proceeds from sale of short-term investments	1,000	1,250
Proceeds from maturity of short-term investments	10,775	11,200
Purchases of short-term investments	(10,125)	(12,450)
Net cash used in investing activities	(843)	(828)
Financing activities
Repayment of lease financing obligations	32	68
Tax withholdings related to net share settlements of restricted stock units	(248)	0
Proceeds from issuance of common stock for employee stock purchase plan	926	767
Proceeds from exercise of stock options	288	269
Net cash provided by financing activities	934	968
Net (decrease) increase in cash and cash equivalents	(15,175)	7,721
Effect of exchange rate changes on cash and cash equivalents	8	10
Cash and cash equivalents
Beginning of period	20,583	21,856
End of period	$ 5,416	$ 29,587