Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (119,126)	$ (119,712)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	18,579	15,628
Depreciation and amortization expense	1,399	1,207
Deferred rent expense	(223)	(183)
Other	49	20
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,018)	1,098
Other assets	362	84
Accounts payable	804	(881)
Accrued expenses and other current liabilities	2,149	3,936
Net cash used in operating activities	(98,025)	(98,803)
Cash flows from investing activities:
Purchases of property and equipment	(2,461)	(1,177)
Net cash used in investing activities	(2,461)	(1,177)
Cash flows from financing activities:
Proceeds from long-term debt	15,000
Payments of issuance cost related to long-term debt	(103)
Exercise of stock options	920	270
Net cash provided by financing activities	30,371	172,619
Net (decrease) increase in cash, cash equivalents and restricted cash	(70,115)	72,639
Cash, cash equivalents and restricted cash at beginning of period	260,174	187,535
Cash, cash equivalents and restricted cash at end of period	190,059	260,174
Supplemental Cash:
Interest paid	98
Supplemental disclosure of non-cash investing and financing activities:
Common stock offering costs incurred but unpaid at period end		205
Reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets:
Cash and cash equivalents, end of period	189,567	259,682
Restricted cash	492	492
Cash, cash equivalents and restricted cash at end of period	190,059	260,174
2018 Employee Stock Purchase Plan [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock, net of offering costs	209	166
Public Offering [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock, net of offering costs	(205)	164,053
ATM Facility [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock, net of offering costs	$ 14,550	$ 8,130