Financial Instruments - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	[1]	$ 121,861	$ 246,947
Restricted cash		198,040	169,763
Cash, cash equivalents and restricted cash		319,901	416,710	$ 504,370	$ 377,388
Cash
Debt Securities, Available-for-sale [Line Items]
Cash, cash equivalents and restricted cash		291,830	180,808
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash, cash equivalents and restricted cash		$ 28,071	$ 235,902

[1] We have variable interest entities, which represent a portion of the consolidated balances recorded within these financial statement line items in the condensed consolidated balance sheets (see Note 11 - Portfolio Financings).