|
Segment Information (Details) (USD $)
|
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
|
Sep. 30, 2012
|
Sep. 30, 2011
|
Sep. 30, 2012
|
Sep. 30, 2011
|
Dec. 31, 2011
|
|
| Segment Reporting Information [Line Items] | |||||
| Number of reportable segments | 1 | ||||
| Net income | $ 58,247,000 | $ 48,581,000 | $ 99,901,000 | $ 83,491,000 | |
| Total assets | 3,465,873,000 | 3,465,873,000 | 3,223,849,000 | ||
|
Regulated Electric [Member]
|
|||||
| Segment Reporting Information [Line Items] | |||||
| Operating revenues from external customers | 471,900,000 | 522,900,000 | 1,192,600,000 | 1,337,400,000 | |
| Net income | 58,200,000 | 48,600,000 | 99,900,000 | 83,500,000 | |
| Capital expenditures | 280,600,000 | 222,300,000 | |||
| Total assets | $ 3,500,000,000 | $ 3,500,000,000 | $ 3,200,000,000 | ||