CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net Loss	$ (151,184)	$ (93,031)	$ (128,530)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	3,577	4,414	3,095
Amortization of Intangible Assets	224	896	997
Amortization and Premium of Marketable Securities, Net	(1,048)	(290)	926
Loss on Sale or Disposal of Assets	1,220	55	81
Goodwill Impairment	90,976
Intangible Asset Impairment	18,677	13,000
Gain on Fair Value Remeasurement of Contingent Consideration	(29,621)	(800)
Non-Cash Income Tax Benefit	(765)	(24,282)
Stock-Based Compensation Expense	8,081	12,312	15,317
Non-Cash Expense			1,638
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(777)	(96)	(814)
Prepaid and Other Current Assets	1,783	793	1,320
Other Assets		205	(89)
Accounts Payable and Accrued Expenses	(13,110)	(8,744)	(4,970)
Other Liabilities	(3,268)	(4,363)	(2,007)
Net Cash Used in Operating Activities	(75,235)	(99,931)	(113,036)
Cash Flows From Investing Activities:
Sales and Maturities of Marketable Securities	201,469	219,236	242,792
Purchases of Marketable Securities	(171,182)	(170,980)	(173,925)
Investment in Other			(1,801)
Cash Acquired in Kolltan Acquisition, Net			4,592
Acquisition of Property and Equipment	(813)	(1,788)	(2,751)
Proceeds from Sale or Disposal of Assets	342
Net Cash Provided by Investing Activities	29,816	46,468	68,907
Cash Flows From Financing Activities:
Net Proceeds from Stock Issuances	29,022	51,025	13,946
Proceeds from Issuance of Stock from Employee Benefit Plans	419	265	536
Net Cash Provided by Financing Activities	29,441	51,290	14,482
Net Decrease in Cash and Cash Equivalents	(15,978)	(2,173)	(29,647)
Cash and Cash Equivalents at Beginning of Period	40,288	42,461	72,108
Cash and Cash Equivalents at End of Period	24,310	40,288	42,461
Non-cash Investing Activities
Accrued construction in progress	107	20	159
Non-cash Supplemental Disclosure
Shares issued to former Kolltan executive for settlement of severance	$ 71	$ 344	426
Shares issued in connection with Kolltan Acquisition			$ 73,397