|
Consolidated Balance Sheets (Parenthetical) (USD $)
In Thousands, except Share data, unless otherwise specified |
Sep. 30, 2014
|
Dec. 31, 2013
|
|---|---|---|
| Statement Of Financial Position [Abstract] | ||
| Utility plant, accumulated depreciation | $ 4,010,604 | $ 3,894,326 |
| Nonutility property, accumulated depreciation | $ 239,780 | $ 215,083 |
| Common stock, par value | $ 0.01 | $ 0.01 |
| Common stock, shares authorized | 500,000,000 | 500,000,000 |
| Common stock, shares outstanding | 179,265,000 | 178,379,000 |