CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (51,000)	$ (49,326)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,303	807
Gain or loss on sale of property and equipment	(8)
Equity-based compensation	7,972	5,211
Amortization/accretion of investment securities	(1,390)	(345)
Non-cash operating lease expense	997
Deferred payroll tax credit	176	272
Change in operating assets and liabilities:
Accounts receivable	(25,000)
Prepaid expenses and other current assets	(739)	(1,276)
Other assets	(98)
Accounts payable	(1,342)	1,664
Accrued expenses	2,453	4,361
Deferred rent		191
Operating lease liabilities	(888)
Deferred revenue	4,508	62,904
Other liabilities	(59)	108
Net cash (used in) provided by operating activities	(63,115)	24,571
Cash flows from investing activities:
Purchase of property and equipment	(3,115)	(1,492)
Purchase of marketable securities	(235,417)	(75,239)
Proceeds from sale of property and equipment	8
Sales and maturities of marketable securities	176,288	16,500
Net cash used in investing activities	(62,236)	(60,231)
Cash flows from financing activities:
Principal payments on loan payable	(365)	(667)
Proceeds from sale of common stock, net of issuance costs	48,348	94,935
Proceeds from stock option exercises	913	6
Other	(13)	(6)
Net cash provided by financing activities	48,883	94,268
Net (decrease) increase in cash and cash equivalents and restricted cash	(76,468)	58,608
Cash and cash equivalents and restricted cash, beginning of period	115,274	56,666
Cash and cash equivalents and restricted cash, end of period	38,806	115,274
Supplemental disclosure of non-cash items:
Property and equipment purchases in accounts payable and accrued expenses		$ 439
Operating lease right-of-use asset obtained in exchange for operating lease obligation	$ 5,444