Power Purchase Agreement Programs - Schedule of VIEs (Details) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) MWh	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Variable Interest Entity [Line Items]
Distributions to Equity Investor	$ 2	$ 566
PPA IIIa
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	10
Installed size (in megawatts) | MWh	10
Term of power purchase agreements (in years)	15 years
Income (loss) and tax benefits allocation to Equity Investor	99.00%
Cash allocation to Equity Investor	99.00%
Income (loss), tax and cash allocations to Equity Investor after the flip date	5.00%
Company cash contributions	$ 32,223
Company non-cash contributions	8,655
Equity Investor cash contributions	36,967
Debt financing	44,968
Distributions to Equity Investor	4,819		$ 4,803
Debt repayment—principal	$ 9,293		6,631
PPA IV
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	21
Installed size (in megawatts) | MWh	19
Term of power purchase agreements (in years)	15 years
Income (loss) and tax benefits allocation to Equity Investor	90.00%
Cash allocation to Equity Investor	90.00%
Company cash contributions	$ 11,669
Company non-cash contributions	0
Equity Investor cash contributions	84,782
Debt financing	99,000
Distributions to Equity Investor	8,582		6,692
Debt repayment—principal	$ 19,534		18,012
PPA V
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	40
Installed size (in megawatts) | MWh	37
Term of power purchase agreements (in years)	15 years
Income (loss) and tax benefits allocation to Equity Investor	99.00%
Cash allocation to Equity Investor	90.00%
Company cash contributions	$ 27,932
Company non-cash contributions	0
Equity Investor cash contributions	227,344
Debt financing	131,237
Distributions to Equity Investor	74,128		70,591
Debt repayment—principal	$ 11,765		$ 9,453