Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (25,408)	$ (27,298)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	1,451	1,107
Stock-based compensation expense	4,309	2,902
Amortization of premium on short-term investments	73	152
Interest accrued on long-term debt	74	0
Conversion of accrued interest to long-term debt	632	538
Loss on sale of property and equipment	0	(2)
Changes in operating assets and liabilities:
Accounts receivable, net	(5,516)	(781)
Inventory	(3,283)	(4,333)
Prepaid expenses and other	260	(1,091)
Other assets	(89)	69
Accounts payable	660	(989)
Accrued liabilities	(2,832)	(3,089)
Deferred revenue	32,314	722
Deferred rent	1,675	828
Net cash provided by (used in) operating activities	4,320	(31,265)
Investing activities
Purchases of property and equipment	(2,231)	(1,564)
Proceeds from sale of property and equipment	0	20
Proceeds from sale of short-term investments	1,250	3,000
Proceeds from maturity of short-term investments	16,700	34,230
Purchases of short-term investments	(28,625)	(19,150)
Net cash (used in) provided by investing activities	(12,906)	16,536
Financing activities
Borrowings under long-term debt agreement	5,000	0
Repayment of lease financing obligations	(135)	(135)
Proceeds from sale of common stock, net	0	12,518
Deferred offering costs	0	(137)
Proceeds from issuance of common stock for employee stock purchase plan	767	664
Proceeds from exercise of stock options	395	352
Net cash provided by financing activities	6,027	13,262
Net decrease in cash and cash equivalents	(2,559)	(1,467)
Effect of exchange rate changes on cash and cash equivalents	(3)	(19)
Cash and cash equivalents
Beginning of period	21,856	17,223
End of period	$ 19,294	$ 15,737