Power Purchase Agreement Programs - Schedule of Consolidated Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	$ 390,273	$ 419,981
Long-term assets	767,464	801,006
Total assets	1,157,737	1,220,987
Current liabilities	218,140	251,148
Current portion of debt	30,006	20,136
Long-term liabilities	544,271	529,135
Long-term portion of debt	930,123	921,205
Total liabilities	1,722,540	1,721,624
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Current assets	28,919	36,772
Long-term assets	516,674	533,656
Total assets	545,593	570,428
Current liabilities	2,837	3,684
Current portion of debt	19,655	18,446
Long-term liabilities	13,134	15,768
Long-term portion of debt	333,102	342,050
Total liabilities	368,728	379,948
Bloom
Variable Interest Entity [Line Items]
Current assets	361,354	383,209
Long-term assets	250,790	267,350
Total assets	612,144	650,559
Current liabilities	215,303	247,464
Current portion of debt	10,351	1,690
Long-term liabilities	531,137	513,367
Long-term portion of debt	597,021	579,155
Total liabilities	$ 1,353,812	$ 1,341,676