Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents
Cash and cash equivalents	$ 334,171	$ 78,823
Transfers between levels
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount	0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	0
Government Backed Securities (REPO)
Cash and Cash Equivalents
Cash and cash equivalents	43,250	20,000
Treasury securities
Cash and Cash Equivalents
Cash and cash equivalents	24,998
Corporate debt securities
Cash and Cash Equivalents
Cash and cash equivalents	59,468
Level 1
Assets
Cash equivalents and marketable securities	79,950	42,960
Level 1 \| Money market funds
Assets
Cash equivalents and marketable securities	79,950	42,960
Level 2
Assets
Cash equivalents and marketable securities	297,577	20,000
Liabilities
Convertible notes payable	389,217	125,811
Level 2 \| Government Backed Securities (REPO)
Assets
Cash equivalents and marketable securities	43,250	$ 20,000
Level 2 \| Treasury securities
Assets
Cash equivalents and marketable securities	65,093
Level 2 \| Corporate debt securities
Assets
Cash equivalents and marketable securities	148,583
Level 2 \| Agency Securities
Assets
Cash equivalents and marketable securities	$ 40,651

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