Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities
Net income (loss)	$ (58,859)	$ 63,087	$ 114,205
Adjustments to reconcile net loss to net cash (used in) provided by operating activities
Depreciation	162	183	2,763
Amortization of premium and discounts on investment securities	0	0	140
Non-cash charge on acquired in-process research and development	0	5,619	0
Gain on sale of property and equipment	(150)	0	0
Non-cash gain on extinguishment of royalty purchase agreement	0	(125,000)	0
Deferred income taxes	0	0	(3,366)
Share-based compensation	9,180	11,072	18,171
Stock-based consideration in connection with license acquisition	85	0	0
Changes in operating assets and liabilities:
Income tax receivable	1,765	1,387	(1,387)
Due from Novartis Pharma AG	0	0	3,531
Prepaid expense and other assets	45	1,070	370
Accrued interest receivable	0	0	466
Accrued research and development expenses	(477)	2,353	(42,256)
Accounts payable and accrued expenses	(241)	(1,682)	(4,481)
Deferred revenue	0	0	(209,977)
Net cash used in operating activities	(48,490)	(41,911)	(121,821)
Investing Activities
Purchase of marketable securities	0	0	(12,014)
Maturities of marketable securities	0	0	166,806
Proceeds from sale of assets	150		0
Net cash provided by investing activities	150	0	154,792
Financing Activities
Proceeds from employee stock plan purchases and stock option exercises	273	65	71
Net cash provided by financing activities	42,838	6,140	71
Net change in cash and cash equivalents	(5,502)	(35,771)	33,042
Cash and cash equivalents
Beginning of period	131,201	166,972	133,930
End of period	125,699	131,201	166,972
Supplemental disclosure of cash paid
Income taxes received, net	(1,893)	(2,467)	(245)
Supplemental disclosures of non-cash information related to investing activities
Change in unrealized gain (loss) on available for sale securities, net of tax	0	0	212
Common stock issued to acquire net assets of Inception 4, Inc.	0	11,694	0
Operating right-of-use assets obtained in exchange for lease obligations	1,469
Public Stock Offering
Financing Activities
Proceeds from issuance of common stock and pre-funded warrants, net	42,565	0	0
Inception 4
Financing Activities
Proceeds from issuance of common stock and pre-funded warrants, net	$ 0	$ 6,075	$ 0