Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (16,864)	$ (6,709)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	196	70
Amortization of intangible assets	499	499
Stock-based compensation	6,403	627
Net premium amortization on investments	24	3
Landlord incentive for tenant improvements	2,119
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(244)	(463)
Accounts payable	649	184
Accrued expenses	207	56
Other asset	(101)
Deferred rent	(12)
Net cash used in operating activities	(7,124)	(5,733)
Cash flows from investing activities:
Purchases of property and equipment	(2,407)	(64)
Purchases of investments	(11,363)	(14,096)
Maturities of investments	16,034
Net cash provided by (used) in investing activities	2,264	(14,160)
Cash flows from financing activities:
Proceeds from issuance of common stock	34,944	20,915
Proceeds from exercise of warrants	50
Proceeds from exercises of stock options	200
Net cash provided by financing activities	35,194	20,915
Net increase in cash	30,334	1,022
Cash and cash equivalents at beginning of period	2,089	3,606
Cash and cash equivalents at end of period	32,423	4,628
Supplemental disclosure of noncash investing and financing activities:
Reclassification of deferred offering costs to additional paid-in capital upon initial public offering		$ 627
Equipment purchased in accrued expenses	109
Financing costs not yet paid	$ 101