Financial Instruments - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2020		Dec. 31, 2019		Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 144,072	[1]	$ 202,823	[1]	$ 308,009
Restricted cash	180,057		174,565
Cash, cash equivalents and restricted cash	324,129		377,388		$ 371,066	$ 280,485
Cash
Debt Securities, Available-for-sale [Line Items]
Cash, cash equivalents and restricted cash	88,092		100,773
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash, cash equivalents and restricted cash	$ 236,037		$ 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).