Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating Activities
Net loss	$ (33,665)	$ (26,944)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and other expense	77	83
Gain on sale of property and equipment	0	(150)
Deferred income taxes	0	0
Share-based compensation	4,197	4,677
Changes in operating assets and liabilities:
Income tax receivable	0	(1)
Prepaid expense and other assets	(155)	302
Accrued research and development expenses	271	308
Accounts payable and accrued expenses	(995)	(2,628)
Net cash used in operating activities	(30,270)	(24,353)
Investing Activities
Net cash provided by (used in) investing activities	0	0
Financing Activities
Proceeds from employee stock plan purchases	186	41
Proceeds from issuance of common stock	150,100
Net cash provided by financing activities	150,306	41
Net change in cash and cash equivalents	120,036	(24,312)
Cash and cash equivalents
Beginning of period	125,699	131,201
End of period	245,735	106,889
Supplemental disclosure of cash paid
Income tax refunds received	3,327	0
Underwritten Offering
Financing Activities
Proceeds from issuance of common stock	116,883	0
Private Placement
Financing Activities
Proceeds from issuance of common stock	$ 33,237	$ 0