Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Utility plant, accumulated depreciation	$ 3,965,888	$ 3,894,326
Nonutility property, accumulated depreciation	$ 243,330	$ 228,465
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000	500,000
Common stock, shares outstanding	179,141	178,379