Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CASH FLOWS USED IN OPERATING ACTIVITIES:
Net loss	$ (27,817)	$ (30,833)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	13	24
Amortization of premium (accretion of discount) on short-term investments, net	14	80
Stock-based compensation expense	785	873
Research and development expense settled in stock	7,255	5,335
Change in fair value of other current assets, warrant liability and other liability	(10,074)	1,184
Non-cash interest	215	199
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	647	1,219
Other long-term assets		35
Accounts payable	1,018	934
Accrued expenses and other current liabilities	8,240	(1,456)
Net cash used in operating activities	(19,704)	(22,406)
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Proceeds from sale of equipment		45
Purchases of marketable securities	(17,070)	(17,722)
Sales and maturities of marketable securities	4,000	22,185
Net cash (used in) provided by investing activities	(13,070)	4,508
CASH FLOWS PROVIDED BY FINANCING ACTIVITIES:
Proceeds from exercise of stock options	13	258
Payments on note payable	(3,938)	(1,125)
Proceeds from the issuance of preferred stock, net	42,870
Proceeds from note payable, net		12,469
Net cash provided by financing activities	38,945	11,602
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	6,171	(6,296)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	18,653	25,128
CASH AND CASH EQUIVALENTS AT END OF PERIOD	24,824	18,832
SUPPLEMENTAL DISCLOSURES:
Cash paid for interest	998	721
NON-CASH FINANCING ACTIVITIES:
Accretion of dividends on preferred stock	7,950	6,810
Fair value of warrants issued	$ 1,356	$ 379