CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (48,557)	$ (23,178)
Adjustments to reconcile net loss to cash used in operating activities:
Non-cash research and development license expense	4,448
Stock-based compensation expense	4,367	1,569
Depreciation and amortization	228	163
Non-cash rent expense	(23)	(56)
Mark to market revaluation of series A investor instrument		1,863
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,760)	(972)
Deferred issuance costs		(1,689)
Accounts payable, accrued expenses and other current liabilities	1,224	830
Due to related parties		(105)
Net cash used in operating activities	(41,073)	(21,575)
Investing activities
Purchases of short-term investments	(188,559)	(13,021)
Maturities of short-term investments	89,463	14,506
Purchases of property, plant and equipment	(327)	(78)
Net cash provided by (used in) investing activities	(99,423)	1,407
Financing activities
Net proceeds from issuance of common stock	162,899
Proceeds from the exercise of stock options	1,634	700
Net proceeds from issuance of Series A Convertible Preferred Stock		40,842
Net cash provided by financing activities	164,533	41,542
Net increase in cash, cash equivalents and restricted cash	24,037	21,374
Cash, cash equivalents and restricted cash at beginning of period	34,461	6,765
Cash, cash equivalents and restricted cash at end of period	$ 58,498	$ 28,139