Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Operating activities
Net loss	$ (27,298)	$ (25,510)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,107	745
Stock-based compensation expense	2,902	2,298
Net amortization of premium on short-term investments	152	(26)
Amortization of debt discount		51
Loss on extinguishment of debt		581
Interest accrued on long-term notes		(348)
Accrued interest converted to principal balance of term loan	538
Loss on sale of property and equipment	(2)
Gain on sale of investments		(2)
Changes in operating assets and liabilities
Accounts receivable, net	(781)	(743)
Inventory	(4,333)	(1,061)
Prepaid expenses and other	(1,091)	(936)
Other assets	69	133
Accounts payable	(989)	(655)
Accrued liabilities	(3,089)	(50)
Deferred revenue	722	5,110
Deferred rent	828	(266)
Net cash used in operating activities	(31,265)	(20,679)
Investing activities
Purchases of property and equipment	(1,564)	(1,236)
Sale of property and equipment	20
Decrease in restricted cash		59
Proceeds from sale of short-term investments	3,000	2,500
Proceeds from maturity of short-term investments	34,230	11,225
Purchases of short-term investments	(19,150)	(39,400)
Net cash provided by (used in) investing activities	16,536	(26,852)
Financing activities
Borrowings under long-term debt agreements		20,000
Deferred costs related to long-term debt agreement		(770)
Repayment of long-term debt	(135)	(18,094)
Deferred offering costs	(137)
Proceeds from public offering, net		57,015
Proceeds from sale of common stock, net	12,518
Proceeds from exercise of common stock warrants		94
Repurchase of shares related to common stock warrant exercise		(94)
Proceeds from issuance of common stock for employee stock purchase plan	664	442
Proceeds from exercise of stock options	352	183
Net cash provided by financing activities	13,262	58,776
Net (decrease) increase in cash and cash equivalents	(1,467)	11,245
Effect of exchange rate changes on cash and cash equivalents	(19)
Cash and cash equivalents
Beginning of period	17,223	9,941
End of period	$ 15,737	$ 21,186