Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Utility plant, accumulated depreciation	$ 3,526,087	$ 3,336,005
Nonutility property, depreciation	$ 180,568	$ 164,417
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000	500,000
Common stock, shares outstanding	176,317	175,664