Basis of Presentation and Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019		Sep. 30, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 176,810	$ 188,425	[1]	$ 164,646	$ 247,577
Restricted cash - non-current assets	917	917	[1]	917	917
Total	$ 177,727	$ 189,342		$ 165,563	$ 248,494

[1] The condensed balance sheet as of December 31, 2019 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019.