Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (85,671)	$ (56,081)
Adjustments to reconcile net loss to net cash used in operating activities:
Noncash stock compensation expense	11,601	7,485
Noncash licensing expense	4,000	0
Depreciation	41	41
Amortization of premium on investment securities	(9)	45
Change in fair value of notes payable	82	84
Changes in assets and liabilities:
Increase in other current assets	(1,213)	(4,252)
Decrease in leasehold interest	53	75
Decrease in accrued interest receivable	22	41
Decrease in other assets	0	395
Increase in accounts payable and accrued expenses	8,898	3,068
Increase in deferred rent	46	45
Decrease in deferred revenue	(76)	(76)
Net cash used in operating activities	(62,226)	(49,130)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of equipment	(58)	(2)
Investment in held-to-maturity securities	(6,965)	0
Proceeds from maturity of short-term securities	14,400	11,000
Net cash provided by investing activities	7,377	10,998
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from the exercise of warrants	0	2,143
Proceeds from sale of common stock, net	104,453	88,562
Net cash provided by financing activities	104,453	90,705
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	49,604	52,573
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	57,305	25,614
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	106,909	78,187
Reconciliation to amounts on consolidated balance sheets:
Total cash, cash equivalents and restricted cash	106,909	25,614
NONCASH TRANSACTIONS
Accrued financing costs	0	234
Reclassification of deferred financing costs to additional paid-in capital	$ 0	$ (3)