Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating activities
Net loss	$ (36,765)	$ (37,658)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,420	1,115
Stock-based compensation expense	4,749	3,604
Net amortization of premium on short-term investments	287	127
Amortization of debt discount	0	51
Loss on extinguishment of debt	0	581
Interest accrued on long-term notes	0	(348)
Accrued interest converted to principal balance of term loan	815	179
Loss on sale of property and equipment	2	0
Gain on sale of investments	0	(5)
Changes in operating assets and liabilities
Accounts receivable, net	(467)	(6,935)
Inventory	(6,769)	(1,198)
Prepaid expenses and other	634	(1,218)
Other assets	104	120
Accounts payable	(857)	(1,210)
Accrued liabilities	(3,013)	667
Deferred revenue	87	9,328
Deferred rent	1,011	(382)
Net cash used in operating activities	(38,762)	(33,182)
Investing activities
Purchases of property and equipment	(1,847)	(1,284)
Sale of property and equipment	20	0
Decrease in restricted cash	0	59
Proceeds from sale of short-term investments	3,000	4,500
Proceeds from maturity of short-term investments	46,178	26,675
Purchases of short-term investments	(23,150)	(47,271)
Net cash provided by (used in) investing activities	24,201	(17,321)
Financing activities
Borrowings under long-term debt agreements	0	20,000
Deferred costs related to long-term debt agreement	0	(770)
Repayment of long-term debt	(203)	(18,151)
Deferred offering costs	(137)	0
Proceeds from public offering, net	0	57,015
Proceeds from sale of common stock, net	12,508	0
Proceeds from exercise of common stock warrants	0	230
Repurchase of shares related to common stock warrant exercise	0	(94)
Proceeds from issuance of common stock for employee stock purchase plan	1,296	988
Proceeds from exercise of stock options	546	170
Net cash provided by financing activities	14,010	59,388
Net (decrease) increase in cash and cash equivalents	(551)	8,885
Effect of exchange rate changes on cash and cash equivalents	(37)	0
Cash and cash equivalents
Beginning of period	17,223	9,941
End of period	$ 16,635	$ 18,826