Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (34,811)	$ (35,496)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	2,478	2,215
Stock-based compensation expense	8,201	6,504
Amortization of premium on short-term investments	113	90
Interest accrued on long-term debt	128	115
Conversion of accrued interest to long-term debt	1,097	993
Provision for bad debt	361	0
(Gain) loss on disposal of property and equipment	1	(2)
Changes in operating assets and liabilities:
Accounts receivable	3,552	(1,320)
Inventory, net	(5,871)	(2,713)
Prepaid expenses and other	(2,284)	(532)
Other assets	(128)	(111)
Accounts payable	(1,714)	(1,178)
Accrued liabilities	7,916	(1,775)
Deferred revenue	(19,608)	31,755
Deferred rent and other liabilities	1,266	1,806
Net cash (used in) provided by operating activities	(39,303)	351
Investing activities
Purchases of property and equipment	(3,805)	(2,709)
Proceeds from sale of property and equipment	0	4
Proceeds from sale of short-term investments	2,300	3,400
Proceeds from maturity of short-term investments	38,324	29,200
Purchases of short-term investments	(48,305)	(48,600)
Net cash used in investing activities	(11,486)	(18,705)
Financing activities
Borrowings under long-term debt agreement	0	5,000
Repayment of lease financing obligations	(58)	(192)
Proceeds from sale of common stock, net	56,486	0
Proceeds from issuance of common stock warrants	175	0
Deferred offering costs	0	(44)
Tax withholdings related to net share settlements of restricted stock units	(309)	0
Proceeds from issuance of common stock for employee stock purchase plan	1,793	1,489
Proceeds from exercise of stock options	892	714
Net cash provided by financing activities	58,979	6,967
Net increase (decrease) in cash and cash equivalents	8,190	(11,387)
Effect of exchange rate changes on cash and cash equivalents	24	(1)
Cash and cash equivalents
Beginning of period	20,583	21,856
End of period	$ 28,797	$ 10,468