Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities
Net loss	$ (35,496)	$ (36,765)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	2,215	1,420
Stock-based compensation expense	6,504	4,749
Amortization of premium on short-term investments	90	287
Interest accrued on long-term debt	115	0
Conversion of accrued interest to long-term debt	993	815
(Gain) loss on sale of property and equipment	(2)	2
Changes in operating assets and liabilities:
Accounts receivable, net	(1,320)	(467)
Inventory	(2,713)	(6,769)
Prepaid expenses and other	(532)	634
Other assets	(111)	104
Accounts payable	(1,178)	(857)
Accrued liabilities	(1,775)	(3,013)
Deferred revenue	31,755	87
Deferred rent	1,806	1,011
Net cash provided by (used in) operating activities	351	(38,762)
Investing activities
Purchases of property and equipment	(2,709)	(1,847)
Proceeds from sale of property and equipment	4	20
Proceeds from sale of short-term investments	3,400	3,000
Proceeds from maturity of short-term investments	29,200	46,178
Purchases of short-term investments	(48,600)	(23,150)
Net cash (used in) provided by investing activities	(18,705)	24,201
Financing activities
Borrowings under long-term debt agreement	5,000	0
Repayment of lease financing obligations	(192)	(203)
Proceeds from sale of common stock, net	0	12,508
Deferred offering costs	(44)	(137)
Proceeds from issuance of common stock for employee stock purchase plan	1,489	1,296
Proceeds from exercise of stock options	714	546
Net cash provided by financing activities	6,967	14,010
Net decrease in cash and cash equivalents	(11,387)	(551)
Effect of exchange rate changes on cash and cash equivalents	(1)	(37)
Cash and cash equivalents
Beginning of period	21,856	17,223
End of period	$ 10,468	$ 16,635