Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (77,762)	$ (53,361)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Stock-based compensation expense	9,182	5,759
Depreciation and amortization	150	318
Amortization expense component of lease expense	445
Noncash expense related to oral formulation license agreement	4,000
Accretion of available-for-sale marketable securities	(1,168)	(1,177)
Realized loss on sale of available-for-sale marketable securities		32
Deferred rent costs		(89)
Deferred revenue	(15,235)	47,542
Changes in operating assets and liabilities:
Income tax receivable	(369)	192
Other receivables	142	(70)
Prepaid expenses	(3,751)	(2,583)
Accounts payable and accrued expenses	6,958	5,497
Operating lease liability	(651)
Net cash (used in) provided by operating activities	(78,059)	2,060
Investing activities
Proceeds from maturities of available-for-sale marketable securities	195,839	85,500
Proceeds from sale of available-for-sale marketable securities		28,250
Purchases of available-for-sale marketable securities	(241,075)	(138,689)
Purchases of property and equipment	(18)	(49)
Net cash used in investing activities	(45,254)	(24,988)
Financing activities
Proceeds from the sale of common stock in a follow-on public offering, net of issuance costs	136,525	92,077
Proceeds from the sale of common stock under license agreement		14,556
Proceeds from the exercise of stock options	6,051	3,636
Net cash provided by financing activities	142,576	110,269
Net increase in cash, cash equivalents and restricted cash	19,263	87,341
Cash, cash equivalents and restricted cash at beginning of period	15,850	10,157
Cash, cash equivalents and restricted cash at end of period	35,113	$ 97,498
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