CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash Flows from Operating Activities:
Net Loss	$ (96,223)	$ (94,513)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	2,135	2,151
Amortization of Intangible Assets	760	760
Amortization and Premium of Marketable Securities, Net	768	(501)
Loss on Sale or Disposal of Assets	74
Stock-Based Compensation Expense	11,709	8,677
Non-Cash Expense	1,638	216
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(609)	(100)
Prepaid and Other Current Assets	(325)	(478)
Other Assets		6
Accounts Payable and Accrued Expenses	(11,560)	(70)
Other Liabilities	(1,054)	(1,290)
Net Cash Used in Operating Activities	(92,687)	(85,142)
Cash Flows from Investing Activities:
Sales and Maturities of Marketable Securities	194,915	129,349
Purchases of Marketable Securities	(149,877)	(193,815)
Investment in Other	(1,801)
Acquisition of Property and Equipment	(2,113)	(4,469)
Net Cash Provided by (Used in) Investing Activities	41,124	(68,935)
Cash Flows from Financing Activities:
Net Proceeds from Stock Issuances	10,666	188,840
Proceeds from Issuance of Stock from Employee Benefit Plans	532	3,993
Net Cash Provided by Financing Activities	11,198	192,833
Effect of Exchange Rate Changes on Cash and Cash Equivalents		15
Net (Decrease) Increase in Cash and Cash Equivalents	(40,365)	38,771
Cash and Cash Equivalents at Beginning of Period	72,108	28,020
Cash and Cash Equivalents at End of Period	31,743	66,791
Non-cash Investing Activities
Acquisition of Property and Equipment included in Accounts Payable and Accrued Expenses	$ 65	$ 38