CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash Flows from Operating Activities:
Net Loss	$ (62,827)	$ (66,625)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	2,367	1,434
Amortization of Intangible Assets	448	507
Amortization and Premium of Marketable Securities, Net	(161)	612
Loss on Sale or Disposal of Assets		74
Loss on Fair Value Remeasurement of Contingent Consideration	4,400
Stock-Based Compensation Expense	6,989	7,913
Non-Cash Expense		1,638
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	425	(146)
Prepaid and Other Current Assets	(511)	(3,124)
Other Assets	199
Accounts Payable and Accrued Expenses	(6,812)	(10,212)
Other Liabilities	(566)	(803)
Net Cash Used in Operating Activities	(56,049)	(68,732)
Cash Flows from Investing Activities:
Sales and Maturities of Marketable Securities	151,470	149,367
Purchases of Marketable Securities	(91,969)	(120,053)
Investment in Other		(1,801)
Acquisition of Property and Equipment	(1,316)	(1,307)
Net Cash Provided by Investing Activities	58,185	26,206
Cash Flows from Financing Activities:
Net Proceeds from Stock Issuances	21,489	2,551
Proceeds from Issuance of Stock from Employee Benefit Plans	76	349
Net Cash Provided by Financing Activities	21,565	2,900
Net Increase (Decrease) in Cash and Cash Equivalents	23,701	(39,626)
Cash and Cash Equivalents at Beginning of Period	42,461	72,108
Cash and Cash Equivalents at End of Period	66,162	32,482
Non-cash Investing Activities
Acquisition of Property and Equipment included in Accounts Payable and Accrued Expenses	87	$ 108
Non-cash Supplemental Disclosure
Shares issued to former Kolltan executive for settlement of severance	$ 263