Basis of Presentation and Summary of Significant Accounting Policies - Carrying Amounts and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Money market funds	$ 115,039	$ 50,731
Marketable securities – certificates of deposit	118,262	116,469
Marketable securities – equity securities	47	70
Total	233,348	167,270
Level 1
Assets
Money market funds	115,039	50,731
Marketable securities – certificates of deposit	118,262	116,469
Marketable securities – equity securities	47	70
Total	233,348	167,270
Level 2
Assets
Money market funds	0	0
Marketable securities – certificates of deposit	0	0
Marketable securities – equity securities	0	0
Total	0	0
Level 3
Assets
Money market funds	0	0
Marketable securities – certificates of deposit	0	0
Marketable securities – equity securities	0	0
Total	$ 0	$ 0