Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities
Net income (loss)	$ (84,547)	$ (58,859)	$ 63,087
Adjustments to reconcile net loss to net cash (used in) provided by operating activities
Depreciation	143	162	183
Amortization of premium and discounts on investment securities	462	0	0
Non-cash charge on acquired in-process research and development	0	0	5,619
Gain on sale of property and equipment	0	(150)	0
Non-cash gain on extinguishment of royalty purchase agreement	0	0	(125,000)
Share-based compensation	8,323	9,180	11,072
Stock-based consideration in connection with license acquisition	0	85	0
Changes in operating assets and liabilities:
Income tax receivable	0	1,765	1,387
Prepaid expense and other assets	(2,742)	45	1,070
Accrued interest receivable	(323)	0	0
Accrued research and development expenses	5,424	(477)	2,353
Accounts payable and accrued expenses	7,163	(241)	(1,682)
Net cash used in operating activities	(66,097)	(48,490)	(41,911)
Investing Activities
Purchase of marketable securities	(143,810)	0	0
Proceeds from sale of assets	0	150	0
Net cash provided by (used in) investing activities	(143,810)	150	0
Financing Activities
Proceeds from employee stock plan purchases and stock option exercises	461	273	65
Net cash provided by financing activities	150,581	42,838	6,140
Net change in cash and cash equivalents	(59,326)	(5,502)	(35,771)
Cash and cash equivalents
Beginning of period	125,699	131,201	166,972
End of period	66,373	125,699	131,201
End of period
Interest	(3,327)	(1,893)	(2,467)
Income taxes received, net
Supplemental disclosures of non-cash information related to investing activities	3	0	0
Common stock issued to acquire net assets of Inception 4, Inc.	0	0	11,694
Operating right-of-use assets obtained in exchange for lease obligations	166	1,469
Public Stock Offering
Financing Activities
Proceeds from issuance of common stock and pre-funded warrants, net, and related to acquisition	116,883	42,565	0
Private Placement
Financing Activities
Proceeds from issuance of common stock and pre-funded warrants, net, and related to acquisition	33,237	0	0
Inception 4
Financing Activities
Proceeds from issuance of common stock and pre-funded warrants, net, and related to acquisition	$ 0	$ 0	$ 6,075