Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating activities
Net loss	$ (11,422)	$ (7,259)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	396	464
Amortization of debt discount	51	51
Stock-based compensation	1,039	231
Revaluation of preferred stock warrant liability		482
Net amortization of premium on short-term investments	(173)
Interest accrued on long-term notes	88	79
Loss on disposal of property and equipment		1
Gain on sale of investments	(2)
Changes in operating assets and liabilities
Accounts receivable	902	(1,034)
Inventory	(772)	43
Prepaid expenses and other	(568)	(842)
Other assets	136	9
Accounts payable	(735)	(62)
Accrued liabilities	(1,651)	(1,201)
Deferred revenue	(217)	211
Deferred rent	(130)	(183)
Net cash used in operating activities	(13,058)	(9,010)
Investing activities
Purchases of property and equipment	(446)	(136)
Decrease in restricted cash	59
Proceeds from maturity of short-term investments	5,671
Purchase of short-term investments	(29,631)
Net cash used in investing activities	(24,347)	(136)
Financing activities
Net proceeds from public offering	57,016
Proceeds from employee stock purchase plan	442
Repayment of long-term debt	(1,129)	(55)
Deferred offering costs		(1,019)
Proceeds from exercise of stock options	108	322
Net cash provided by (used in) financing activities	56,437	(752)
Net increase (decrease) in cash and cash equivalents	19,032	(9,898)
Cash and cash equivalents
Beginning of period	9,941	21,692
End of period	$ 28,973	$ 11,794