Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents
Cash and cash equivalents	$ 1,936,998	$ 553,398
Treasury securities
Cash and Cash Equivalents
Cash and cash equivalents	99,996	44,052
Corporate debt securities
Cash and Cash Equivalents
Cash and cash equivalents	1,159,729	246,668
Level 1
Assets
Total cash equivalents and marketable securities	366,242	96,116
Liabilities
Convertible notes payable	0	0
Level 1 | Money market funds
Assets
Total cash equivalents and marketable securities	366,242	96,116
Level 1 | Government-backed securities
Assets
Total cash equivalents and marketable securities	0	0
Level 1 | Treasury securities
Assets
Total cash equivalents and marketable securities	0	0
Level 1 | Corporate debt securities
Assets
Total cash equivalents and marketable securities	0	0
Level 1 | Agency securities
Assets
Total cash equivalents and marketable securities	0	0
Level 2
Assets
Total cash equivalents and marketable securities	1,456,975	492,619
Liabilities
Convertible notes payable	559,722	407,238
Level 2 | Money market funds
Assets
Total cash equivalents and marketable securities	0	0
Level 2 | Government-backed securities
Assets
Total cash equivalents and marketable securities	197,250	44,250
Level 2 | Treasury securities
Assets
Total cash equivalents and marketable securities	99,996	54,088
Level 2 | Corporate debt securities
Assets
Total cash equivalents and marketable securities	1,159,729	373,681
Level 2 | Agency securities
Assets
Total cash equivalents and marketable securities	0	20,600
Level 3
Assets
Total cash equivalents and marketable securities	0	0
Liabilities
Convertible notes payable	0	0
Level 3 | Money market funds
Assets
Total cash equivalents and marketable securities	0	0
Level 3 | Government-backed securities
Assets
Total cash equivalents and marketable securities	0	0
Level 3 | Treasury securities
Assets
Total cash equivalents and marketable securities	0	0
Level 3 | Corporate debt securities
Assets
Total cash equivalents and marketable securities	0	0
Level 3 | Agency securities
Assets
Total cash equivalents and marketable securities	$ 0	$ 0