CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Cash Flows from Operating Activities:
Net Loss	$ (58,177)	$ (36,348)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	1,161	943
Amortization of Intangible Assets	507	507
Amortization and Premium of Marketable Securities	(1,436)	(1,949)
Gain (Loss) on Sales or Disposal of Assets		(21)
Stock-Based Compensation Expense	2,761	1,384
Non-Cash Interest Expense		97
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(36)	32
Prepaid and Other Current Assets	(1,825)	(424)
Other Assets	32	250
Accounts Payable and Accrued Expenses	(1,033)	109
Other Liabilities	5,315	162
Net Cash Used in Operating Activities	(52,731)	(35,258)
Cash Flows from Investing Activities:
Sales and Maturities of Marketable Securities	50,587	20,582
Purchases of Marketable Securities	(126,222)	(88,845)
Acquisition of Property and Equipment	(1,094)	(917)
Proceeds from Sales or Disposal of Assets		21
Net Cash Used in Investing Activities	(76,729)	(69,159)
Cash Flows from Financing Activities:
Net Proceeds from Stock Issuances		114,187
Proceeds from Issuance of Stock from Employee Benefit Plans	856	2,294
Payments of Term Loan		(11,029)
Payments of Other Liabilities		(29)
Net Cash Provided by Financing Activities	856	105,423
Effect of Exchange Rate Changes on Cash and Cash Equivalents	(1)	(3)
Net (Decrease) Increase in Cash and Cash Equivalents	(128,605)	1,003
Cash and Cash Equivalents at Beginning of Period	169,402	24,897
Cash and Cash Equivalents at End of Period	$ 40,797	$ 25,900