Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (35,465)	$ (19,881)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	3,624	1,959
Depreciation and amortization expense	1,476	1,802
Non-cash operating lease cost	655	536
Accretion of discount on investments	851	(66)
Non-cash interest expense	118	314
Changes in operating assets and liabilities:
Prepaid expenses and other current and long-term assets	(1,402)	203
Accounts receivable	6,783	(237)
Deferred revenue	(4,648)	(6,634)
Accounts payable	973	590
Operating lease liabilities	(1,232)	(1,066)
Accrued expenses and other current and long-term liabilities	(1,229)	(1,771)
Net cash used in operating activities	(29,496)	(24,251)
Cash flows from investing activities:
Purchases of property and equipment	(1,342)	(71)
Purchases of investments	(46,944)	(12,931)
Sales and maturities of investments	27,548	22,439
Net cash (used in) provided by investing activities	(20,738)	9,437
Cash flows from financing activities:
Proceeds from exercise of stock options	372	60
Proceeds from issuance of common stock and restricted common stock		120
Proceeds from at the market equity offering, net of commissions		4,116
Issuance of common stock under ESPP plan	392	249
Net cash provided by financing activities	764	4,545
Net decrease in cash and cash equivalents	(49,470)	(10,269)
Cash, cash equivalents and restricted cash at beginning of period	116,049	65,126
Cash, cash equivalents and restricted cash at end of period	66,579	54,857
Supplemental disclosure of cash flow information:
Cash paid for interest	603	610
Supplemental disclosure of non-cash investing and financing activities:
Unsettled issuance of common stock from the at the market offering		62
Property and equipment purchases included in accounts payable and accrued expenses	$ 268	$ 133