Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating Activities:
Net loss	$ (22,098)	$ (18,480)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	400	445
Amortization of premium on marketable securities	843	625
Stock-based compensation	6,165	4,098
Change in fair value of contingent consideration liability	130
Net changes in operating assets and liabilities:
Interest receivable	25	(18)
Accounts receivable	(5,319)	(696)
Prepaid expenses and other assets	(1,059)	(387)
Accounts payable and accrued liabilities	3,619	(1,348)
Accrued compensation and employee benefits	(530)	(434)
Deferred revenues	14,861	(1,630)
Net cash used in operating activities	(2,963)	(17,825)
Investing Activities:
Purchases of marketable securities	(176,385)	(37,161)
Maturities of marketable securities	76,605	38,384
Purchases of property and equipment	(559)	(395)
Net cash provided by / (used in) investing activities	(100,339)	828
Financing Activities:
Proceeds from public offering of common stock, net of issuance costs	93,796	69,492
Proceeds from issuance of common stock	10,525	6,135
Net cash provided by financing activities	104,321	75,627
Net increase in cash and cash equivalents	1,019	58,630
Cash and cash equivalents, beginning of period	10,186	21,679
Cash and cash equivalents, end of period	$ 11,205	$ 80,309