Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net loss	$ (14,894)	$ (11,422)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	485	396
Stock-based compensation expense	1,252	1,039
Net amortization of premium on short-term investments	88	(173)
Amortization of debt discount	0	51
Interest accrued on long-term notes	0	88
Accrued interest converted to principal balance of term loan	267	0
Gain on sale of investments	0	(2)
Changes in operating assets and liabilities
Accounts receivable, net	1,966	902
Inventory	(2,690)	(772)
Prepaid expenses and other	(226)	(568)
Other assets	35	136
Accounts payable	1,097	(735)
Accrued liabilities	(3,747)	(1,651)
Deferred revenue	(663)	(217)
Deferred rent	310	(130)
Net cash used in operating activities	(16,720)	(13,058)
Investing activities
Purchases of property and equipment	(632)	(446)
Decrease in restricted cash	0	59
Proceeds from sale of short-term investments	3,000	5,671
Proceeds from maturity of short-term investments	22,679	0
Purchases of short-term investments	(11,900)	(29,631)
Net cash provided by (used) in investing activities	13,147	(24,347)
Financing activities
Repayment of long-term debt	(68)	(1,129)
Proceeds from public offering	0	57,016
Proceeds from issuance of common stock for employee stock purchase plan	664	442
Proceeds from exercise of stock options	82	108
Net cash provided by financing activities	678	56,437
Net (decrease) increase in cash and cash equivalents	(2,895)	19,032
Effect of exchange rate changes on cash and cash equivalents	20	0
Cash and cash equivalents
Beginning of period	17,223	9,941
End of period	$ 14,348	$ 28,973