STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating Activities:
Net loss	$ (31,674)	$ (22,630)
Reconciliation of net loss to net cash used in operating activities:
Change in fair value of warrant liability		(267)
Depreciation and amortization	1,956	961
Amortization of net premiums on investments	(80)	232
Loss (gain) on disposal of property and equipment	4	(43)
Deferred rent	(45)	458
Non-cash stock-based compensation	2,892	1,121
Realized gains on investments	(615)
Changes in operating assets and liabilities:
Restricted cash	1,214	986
Accounts receivable - billed	(1,828)	104
Accounts receivable - unbilled	149	(245)
Prepaid expenses and other assets	(1,823)	702
Accounts payable and accrued expenses	(1,279)	(40)
Deferred revenue	(243)	(258)
Lease incentives received		703
Net cash used in operating activities	(31,372)	(18,216)
Investing Activities:
Capital expenditures	(1,846)	(3,157)
Proceeds from disposal of property and equipment	12	81
Proceeds from maturities of investments	13,440	9,649
Purchases of investments	(104,686)	(14,754)
Net cash used in investing activities	(93,080)	(8,181)
Financing Activities:
Principal payments on capital leases	(32)	(29)
Principal payments on notes payable	(338)	(136)
Proceeds from notes payable		1,450
Changes in restricted cash	(1)	(1)
Cash paid with the Novavax AB acquisition	(171)
Net proceeds from sales of common stock, net of offering costs of $7.1 million and $0.3 million, respectively	107,900	10,018
Proceeds from the exercise of stock options and employee stock purchases	1,510	270
Net cash provided by financing activities	108,868	11,572
Effect of exchange rate on cash and cash equivalents	(30)
Net decrease in cash and cash equivalents	(15,614)	(14,825)
Cash and cash equivalents at beginning of period	119,471	17,399
Cash and cash equivalents at end of period	103,857	2,574
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	840	1,026
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 100	$ 61