Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (70,499)	$ (77,762)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	10,770	9,182
Depreciation and amortization	147	150
Amortization expense component of lease expense	496	445
Noncash expense related to oral formulation license agreement		4,000
Amortization/(Accretion) of available-for-sale marketable securities, net	28	(1,168)
Realized gain on sale of available-for-sale marketable securities	(126)
Deferred revenue	(21,751)	(15,235)
Changes in operating assets and liabilities:
Income tax receivable	(436)	(369)
Other receivables	509	142
Prepaid expenses	(1,391)	(3,751)
Accounts payable and accrued expenses	(4,608)	6,958
Operating lease liability	(714)	(651)
Net cash used in operating activities	(87,575)	(78,059)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	119,895	195,839
Proceeds from redemptions of available-for-sale marketable securities, at par	22,035
Proceeds from sale of available-for-sale marketable securities	23,148
Purchases of available-for-sale marketable securities	(21,016)	(241,075)
Purchases of property and equipment	(182)	(18)
Net cash provided by (used in) investing activities	143,880	(45,254)
Financing activities
Proceeds from the sale of common stock in a follow-on public offering, net of issuance costs		136,525
Proceeds from the exercise of stock options	671	6,051
Net cash provided by financing activities	671	142,576
Net increase in cash, cash equivalents and restricted cash	56,976	19,263
Cash, cash equivalents and restricted cash at beginning of period	18,713	15,850
Cash, cash equivalents and restricted cash at end of period	$ 75,689	35,113
Noncash investing and financing activities
Shares of common stock issued in connection with oral formulation license agreement		4,000
Shares of common stock issued in exchange for consulting services		$ 197