CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash Flows from Operating Activities:
Net Loss	$ (86,258)	$ (59,488)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	1,764	1,422
Amortization of Intangible Assets	760	760
Amortization and Premium of Marketable Securities	(754)	(1,232)
Realized Gain on Sales and Maturities of Marketable Securities	(11)
Gain (Loss) on Sales or Disposal of Assets		(21)
Stock-Based Compensation Expense	4,719	3,400
Non-Cash Interest Expense		97
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(2,416)	(846)
Prepaid and Other Current Assets	(1,428)	(1,457)
Other Assets	49	267
Accounts Payable and Accrued Expenses	(740)	2,954
Other Liabilities	4,992	1,432
Net Cash Used in Operating Activities	(79,323)	(52,712)
Cash Flows from Investing Activities:
Sales and Maturities of Marketable Securities	89,215	30,679
Purchases of Marketable Securities	(146,159)	(92,400)
Acquisition of Property and Equipment	(1,766)	(1,901)
Proceeds from Sales or Disposal of Assets		21
Net Cash Used in Investing Activities	(58,710)	(63,601)
Cash Flows from Financing Activities:
Net Proceeds from Stock Issuances		114,187
Proceeds from Issuance of Stock from Employee Benefit Plans	1,160	2,931
Payments of Term Loan		(11,029)
Payments of Other Liabilities		(44)
Net Cash Provided by Financing Activities	1,160	106,045
Effect of Exchange Rate Changes on Cash and Cash Equivalents	(4)	(3)
Net Decrease in Cash and Cash Equivalents	(136,877)	(10,271)
Cash and Cash Equivalents at Beginning of Period	169,402	24,897
Cash and Cash Equivalents at End of Period	$ 32,525	$ 14,626