Power Purchase Agreement Programs - Schedule of VIEs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) MWh	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Distributions to Equity Investor	$ (373)	$ (576)	$ (576)
PPA II
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	30
Term of power purchase agreements (in years)	21 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%
Installed size (in megawatts) | MWh	0
Company cash contributions	$ 22,442
Company non-cash contributions	0
Equity Investor cash contributions	139,993
Distributions to Equity Investor	(176,364)	(116,942)	(111,296)
Debt financing	144,813
Debt repayment—principal	$ 144,813	65,114	53,726
PPA IIIa
Variable Interest Entity [Line Items]
Maximum size of installation (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%
Installed size (in megawatts) | MWh	10
Company cash contributions	$ 32,223
Company non-cash contributions	8,655
Equity Investor cash contributions	36,967
Distributions to Equity Investor	(4,803)	(4,063)	(3,324)
Debt financing	44,968
Debt repayment—principal	$ 6,631	4,431	3,041
PPA IIIb
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	6
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%
Installed size (in megawatts) | MWh	0
Company cash contributions	$ 22,658
Company non-cash contributions	2,082
Equity Investor cash contributions	20,152
Distributions to Equity Investor	(4,462)	(1,807)	(1,404)
Debt financing	28,676
Debt repayment—principal	$ 28,676	3,953	3,077
PPA IV
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	21
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%
Installed size (in megawatts) | MWh	19
Company cash contributions	$ 11,669
Company non-cash contributions	0
Equity Investor cash contributions	84,782
Distributions to Equity Investor	(6,692)	(4,568)	(2,565)
Debt financing	99,000
Debt repayment—principal	$ 18,012	15,543	13,697
PPA V
Variable Interest Entity [Line Items]
Maximum size of installation (in megawatts) | MWh	40
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%
Installed size (in megawatts) | MWh	37
Company cash contributions	$ 27,932
Company non-cash contributions	0
Equity Investor cash contributions	227,344
Distributions to Equity Investor	(70,591)	(66,745)	(60,286)
Debt financing	131,237
Debt repayment—principal	$ 9,453	$ 5,780	$ 2,834