CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (25,223)	$ (24,317)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	386	347
Gain on sale of assets	(1,604)	(1,595)
Deferred revenues	0	(1,460)
Deferred rent	12	76
Amortization of premiums on investments	1,594	1,358
Non-cash share-based compensation expense	5,274	3,412
Change in operating assets and liabilities:
Receivables under collaboration agreements and other assets	(196)	14,094
Accounts payable and accrued liabilities	229	528
Cease-use liability	(204)	(391)
Net cash used in operating activities	(19,732)	(7,948)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of investments	(208,337)	(95,612)
Sales and maturities of investments	85,069	81,819
Proceeds from sales of property and equipment	45	0
Deposits and restricted cash	0	32
Purchases of property and equipment	(904)	(323)
Net cash used in investing activities	(124,127)	(14,084)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of common stock	136,515	2,591
Net cash provided by financing activities	136,515	2,591
Net decrease in cash and cash equivalents	(7,344)	(19,441)
Cash and cash equivalents at beginning of the period	44,789	63,754
Cash and cash equivalents at end of the period	$ 37,445	$ 44,313