Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) - USD ($) $ in Thousands |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Property, Plant and Equipment [Line Items] | ||
| Property, plant and equipment, gross | $ 4,627,864 | $ 4,747,351 |
| Less: accumulated depreciation | (830,766) | (782,230) |
| Property, plant and equipment, net | 3,797,098 | 3,965,121 |
| Operating Wind Farms [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property, plant and equipment, gross | 4,521,482 | 4,640,718 |
| Transmission Line [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property, plant and equipment, gross | 93,849 | 93,849 |
| Furniture, Fixtures and Equipment [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property, plant and equipment, gross | 12,285 | 12,643 |
| Land [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property, plant and equipment, gross | $ 248 | $ 141 |