Revenue - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands |
3 Months Ended |
6 Months Ended |
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
$ 139,940
|
$ 107,760
|
$ 251,599
|
$ 208,593
|
| Electricity Sales Under PSA [Member] |
|
|
|
|
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
17,414
|
16,580
|
38,100
|
35,401
|
| Electricity Sales To Market [Member] |
|
|
|
|
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
4,536
|
3,116
|
6,729
|
6,515
|
| Renewable Energy Credits Sales [Member] |
|
|
|
|
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
3,398
|
2,044
|
5,345
|
4,326
|
| Electricity And REC Sales [Member] |
|
|
|
|
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
25,348
|
21,740
|
50,174
|
46,242
|
| Other Electricity Sales [Member] |
|
|
|
|
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
110,603
|
83,996
|
187,924
|
157,928
|
| Other Revenue, Related Party [Member] |
|
|
|
|
| Disaggregation of Revenue [Line Items] |
|
|
|
|
| Total revenue from contracts with customers |
$ 3,989
|
$ 2,024
|
$ 13,501
|
$ 4,423
|