Cash, Concentration of Credit Risk and Fair Value of Financial Instruments - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Assets:
Total	$ 912,268	$ 948,569
Amount of commercial paper included in cash and cash equivalents	833,533	706,282	$ 410,144
U.S. government securities
Assets:
Securities	43,188	51,301
Corporate bonds, asset backed and other securities
Assets:
Securities	13,895	33,091
Money market and demand accounts
Assets:
Cash and cash equivalents	845,192	705,725
Commercial Paper
Assets:
Cash and cash equivalents	9,993	158,452
Amount of commercial paper included in cash and cash equivalents	0	7,500
Level 1
Assets:
Total	845,192	705,725
Level 1 | U.S. government securities
Assets:
Securities	0	0
Level 1 | Corporate bonds, asset backed and other securities
Assets:
Securities	0	0
Level 1 | Money market and demand accounts
Assets:
Cash and cash equivalents	845,192	705,725
Level 1 | Commercial Paper
Assets:
Cash and cash equivalents	0	0
Level 2
Assets:
Total	67,076	242,844
Level 2 | U.S. government securities
Assets:
Securities	43,188	51,301
Level 2 | Corporate bonds, asset backed and other securities
Assets:
Securities	13,895	33,091
Level 2 | Money market and demand accounts
Assets:
Cash and cash equivalents	0	0
Level 2 | Commercial Paper
Assets:
Cash and cash equivalents	9,993	158,452
Level 3
Assets:
Total	0	0
Level 3 | U.S. government securities
Assets:
Securities	0	0
Level 3 | Corporate bonds, asset backed and other securities
Assets:
Securities	0	0
Level 3 | Money market and demand accounts
Assets:
Cash and cash equivalents	0	0
Level 3 | Commercial Paper
Assets:
Cash and cash equivalents	$ 0	$ 0