Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (35,156)	$ (41,529)
Adjustments to reconcile net loss to net cash used in operating activities:
Noncash stock compensation expense	1,882	7,337
Depreciation	23	20
Amortization of premium on investment securities	(75)	2
Amortization of debt issuance costs	77	0
Non-cash change in lease liability and right-of-use asset	373	0
Change in fair value of notes payable and accrued interest	66	96
Changes in assets and liabilities:
(Increase) decrease in prepaid research and development and other current assets	(2,454)	691
Decrease in leasehold interest	46	33
Decrease in lease liability	(339)	0
Decrease in accrued interest receivable	14	30
Increase in accounts payable and accrued expenses	2,240	5,292
Increase in interest payable	549	0
Decrease in other current liabilities	(559)	0
Increase in deferred rent	0	23
Decrease in deferred revenue	(38)	(38)
Net cash used in operating activities	(33,351)	(28,043)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of equipment	(14)	(24)
Investment in held-to-maturity securities	(8,171)	(4,184)
Proceeds from maturity of short-term securities	7,050	6,000
Net cash (used in) provided by investing activities	(1,135)	1,792
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from sale of common stock, net	27,678	52,430
Proceeds from debt financings	29,740	0
Financing costs paid	(538)	0
Net cash provided by financing activities	56,880	52,430
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	22,394	26,179
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	43,199	57,305
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	65,593	83,484
Reconciliation to amounts on consolidated balance sheets:
Total cash, cash equivalents and restricted cash	65,593	57,305
NONCASH TRANSACTIONS
Accrued offering costs	179	0
Deferred financing costs	1,157	0
Warrants issued with debt financing	$ 993	$ 0