Financial Instruments - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Variable Interest Entity [Line Items]
Restricted cash, current	$ 30,804	[1]	$ 14,486	$ 23,706	$ 18,419	$ 28,657	$ 28,657	[1]	$ 17,931	$ 25,860	$ 22,998
Restricted cash, non-current	143,761	[1]	$ 116,890	$ 39,351	$ 31,101	$ 31,100	31,100	[1]	$ 30,779	$ 32,416	$ 32,367
Total restricted cash	174,565						59,757
Consolidated Entity, Excluding VIEs
Variable Interest Entity [Line Items]
Restricted cash, current	28,494						25,740
Restricted cash, non-current	10						3,246
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Restricted cash, current	2,244						2,917
Restricted cash, non-current	15,045						27,854
PPA Entities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Restricted cash, current	2,310						2,917
Restricted cash, non-current	143,751						$ 27,854
PPA II | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Restricted cash, non-current	108,700
PPA IIIb | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Restricted cash, non-current	$ 20,000

[1] We have variable interest entities which represent a portion of the consolidated balances are recorded within these financial statement line items in the Consolidated Balance Sheets (see Note 13, Power Purchase Agreement Programs).