Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 12,377	$ 12,772
Letter of Credit
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	5,100	5,100
Initial Capitalization
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	1,500	1,500
Insurance Premiums
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 5,700	$ 6,100