CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash Flows from Operating Activities:
Net Loss	$ (34,261)	$ (34,673)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	1,366	742
Amortization of Intangible Assets	224	253
Amortization and Premium of Marketable Securities, Net	(23)	529
Loss on Sale or Disposal of Assets		70
Loss on Fair Value Remeasurement of Contingent Consideration	3,400
Stock-Based Compensation Expense	3,539	3,940
Non-Cash Expense		1,638
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	400	123
Prepaid and Other Current Assets	(989)	(1,741)
Other Assets	199
Accounts Payable and Accrued Expenses	(8,315)	(4,957)
Other Liabilities	(802)	(826)
Net Cash Used in Operating Activities	(35,262)	(34,902)
Cash Flows from Investing Activities:
Sales and Maturities of Marketable Securities	73,736	74,939
Purchases of Marketable Securities	(50,961)	(48,860)
Acquisition of Property and Equipment	(374)	(540)
Net Cash Provided by Investing Activities	22,401	25,539
Cash Flows from Financing Activities:
Net Proceeds from Stock Issuances	12,821
Proceeds from Issuance of Stock from Employee Benefit Plans	76	280
Net Cash Provided by Financing Activities	12,897	280
Net Increase (Decrease) in Cash and Cash Equivalents	36	(9,083)
Cash and Cash Equivalents at Beginning of Period	42,461	72,108
Cash and Cash Equivalents at End of Period	42,497	63,025
Non-cash Investing Activities
Acquisition of Property and Equipment included in Accounts Payable and Accrued Expenses	370	$ 278
Non-cash Supplemental Disclosure
Shares issued to former Kolltan executive for settlement of severance	$ 209