Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (50,139)	$ (40,038)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	9,920	8,017
Depreciation and amortization	1,929	1,994
Provision for credit losses	565	0
Net amortization of premiums on marketable securities	1,288	39
Net realized and unrealized losses (gains) on marketable securities	(7)	5,111
Imputed interest income from licensing	(29)	(848)
Non-cash interest expense	6,702
Other non-cash adjustments	(154)	25
Changes in operating assets and liabilities
Accounts receivable	1,618	(5,744)
Prepaid expenses	(3,334)	(947)
Other current assets	(873)	(2,833)
Operating lease right-of-use assets	1,232	703
Other assets	(3,789)	1,705
Accounts payable	278	3,063
Accrued expenses and other current liabilities	(10,544)	(3,813)
Operating lease liabilities	4,244	(851)
Other liabilities	(38)	(1,156)
Net cash used in operating activities	(41,131)	(35,573)
Cash flows from investing activities
Purchases of marketable debt securities	(233,627)	(30,692)
Maturities of marketable debt securities	50,465	60,907
Sales of marketable equity securities		7,124
Purchases of property and equipment	(31,021)	(4,630)
Net cash provided by (used in) investing activities	(214,183)	32,709
Cash flows from financing activities
Proceeds from exercise of stock options	1,292	2,154
Proceeds from issuance of common stock under employee stock purchase plan	627	607
Proceeds from public offering of common stock, net of underwriting discounts and commissions	216,438
Issuance costs for public offerings of common stock	(251)
Repayments under liability related to sale of future royalties	(9,471)
Transaction costs for sale of future royalties	(265)
Net cash provided by financing activities	208,370	2,761
Net decrease in cash and cash equivalents and restricted cash	(46,944)	(103)
Cash and cash equivalents and restricted cash
Beginning of period	339,756	70,844
End of period	292,812	$ 70,741
Supplemental disclosures of non-cash investing and financing activities
Additions to property and equipment through accounts payable and accrued expenses	$ 3,783