Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flow from operating activities:
Net loss	$ (37,315)	$ (20,965)	$ (19,175)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,150	1,234	1,549
Stock-based compensation and 401(k) Plan employer match	3,270	1,364	1,634
Fair value adjustment of common stock warrants	(555)	(3,560)	(6,422)
Loss / (gain) on disposal of equipment	42	45	(16)
Changes in:
Inventory	(195)	0	0
Prepaid expenses and other current assets	(277)	(157)	(52)
Accounts payable	55	(574)	391
Accrued expenses	1,187	(314)	(166)
Other assets	0	174	4
Other liabilities and accrued interest on loan payable	(246)	55	(2,017)
Net cash used in operating activities	(32,884)	(22,698)	(24,270)
Cash flow from investing activities:
Purchase of property and equipment	(636)	(106)	(101)
Net cash used in investing activities	(636)	(106)	(101)
Cash flow from financing activities:
Proceeds from issuance of securities, net of expenses	43,551	22,927	27,977
Proceeds from exercise of common stock warrants	6,741	0	0
Proceeds from exercise of stock options	6	0	0
Principal payments of loan payable	0	0	(8,500)
Principal payments under equipment loan and capital lease obligations	(75)	(145)	(636)
Net cash provided by financing activities	50,223	22,782	18,841
Net increase (decrease) in cash and cash equivalents	16,703	(22)	(5,530)
Cash and cash equivalents as of beginning of year	10,189	10,211	15,741
Cash and cash equivalents as of end of year	26,892	10,189	10,211
Supplementary disclosure of cash flows information:
Interest paid	13	20	2,123
Equipment acquired through capitalized lease	$ 0	$ 0	$ 48