Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities
Net loss	$ (25,510)	$ (12,754)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	745	901
Stock-based compensation	2,298	488
Net amortization of premium on short-term investments	(26)
Amortization of debt discount	51	110
Revaluation of preferred stock warrant liability		(1,156)
Loss on extinguishment of debt	581
Interest accrued on long-term notes	(348)	99
Loss on disposal of property and equipment		1
Gain on sale of investments	(2)
Changes in operating assets and liabilities
Accounts receivable	(743)	(1,457)
Inventory	(1,061)	(247)
Prepaid expenses and other	(936)	(1,213)
Other assets	133	(131)
Accounts payable	(655)	826
Accrued liabilities	(50)	329
Deferred revenue	5,110	335
Deferred rent	(266)	(373)
Net cash used in operating activities	(20,679)	(14,242)
Investing activities
Purchases of property and equipment	(1,236)	(254)
Decrease in restricted cash	59
Proceeds from sale of short-term investments	2,500
Proceeds from maturity of short-term investments	11,225
Purchase of short-term investments	(39,400)
Net cash used in investing activities	(26,852)	(254)
Financing activities
Borrowings under long-term debt agreements	20,000	5,000
Deferred costs related to long-term debt agreement	(770)
Repayment of long-term debt	(18,094)	(109)
Net proceeds from public offering	57,015
Deferred offering costs		(1,705)
Proceeds from exercise of common stock warrants	94
Repurchase of shares related to common stock warrant exercise	(94)
Proceeds from employee stock purchase plan	442
Proceeds from exercise of stock options	183	373
Net cash provided by financing activities	58,776	3,559
Net increase (decrease) in cash and cash equivalents	11,245	(10,937)
Cash and cash equivalents
Beginning of period	9,941	21,692
End of period	$ 21,186	$ 10,755