Financial Instruments - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020		Dec. 31, 2019		Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 325,241	[1]	$ 202,823	[1]	$ 226,499
Restricted cash	179,128		174,565
Cash, cash equivalents and restricted cash	504,369		377,388		$ 357,875	$ 280,485
Cash
Debt Securities, Available-for-sale [Line Items]
Cash, cash equivalents and restricted cash	66,135		100,773
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash, cash equivalents and restricted cash	$ 438,234		$ 276,615

[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 13, Power Purchase Agreement Programs).