Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (119,622)	$ (87,616)
Adjustments to reconcile net loss to net cash used in operating activities:
Noncash stock compensation expense	11,428	12,375
Noncash licensing expense	4,000	0
Depreciation	64	62
Amortization of premium on investment securities	(51)	54
Change in fair value of notes payable	(37)	113
Changes in assets and liabilities:
(Increase) decrease in other current assets	(3,421)	148
Decrease in leasehold interest	98	88
Decrease in accrued interest receivable	28	84
Decrease in other assets	0	162
Increase in accounts payable and accrued expenses	12,321	2,666
Increase in deferred rent	71	73
Decrease in deferred revenue	(114)	(114)
Net cash used in operating activities	(95,235)	(71,905)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property, plant and equipment	(84)	(2)
Investment in held-to-maturity securities	(24,574)	0
Proceeds from maturity of short-term securities	25,600	19,800
Net cash provided by investing activities	942	19,798
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from the exercise of warrants	0	2,143
Proceeds from sale of common stock, net	108,945	116,778
Net cash provided by financing activities	108,945	118,921
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	14,652	66,814
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	57,305	25,614
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	71,957	92,428
Reconciliation to amounts on consolidated balance sheets:
Total cash, cash equivalents and restricted cash	71,957	25,614
NONCASH TRANSACTIONS
Reclassification of deferred financing costs to additional paid-in capital	$ 0	$ (3)