CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating activities
Net loss	$ (24,081)	$ (17,434)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	145	165
Stock-based compensation expense	2,153	1,700
Non-cash interest expense	242	200
Warrant modification expense	41	511
Changes in operating assets and liabilities:
Grant and other receivables	1,219	108
Prepaid expenses and other current and noncurrent assets	(72)	(378)
Accounts payable and accrued expenses	1,001	(62)
Deferred Offering Costs	0	(235)
Deferred revenue	(970)	(1,950)
Other Liabilities	1,961	3,009
Net cash used in operating activities	(18,361)	(14,366)
Investing activities
Purchases of property and equipment	(89)	(145)
Purchases of investments	(19,617)	0
Proceeds from the sale of investments	22,101	20,565
Net cash provided by investing activities	2,395	20,420
Financing activities
Proceeds from issuance of common stock upon direct offering	16,120	0
Payments on notes payable	0	(3,031)
Proceeds from issuance of common stock upon exercise of stock options	42	240
Net cash provided by (used in) financing activities	16,162	(2,791)
Net increase in cash and cash equivalents	196	3,263
Cash and cash equivalents at beginning of period	1,520	4,005
Cash and cash equivalents at end of period	1,716	7,268
Supplemental cash flow information
Cash paid for interest	778	769
Reduction of equipment cost basis due to assets purchased with grant funding	$ 0	$ 59