Summary of Significant Accounting Policies, Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Regulated utility plants	$ 3,815,608	$ 3,759,541
Other	267,028	264,114
Property, plant and equipment	4,082,636	4,023,655
Accumulated depreciation	(1,291,862)	(1,230,783)
Net property, plant, and equipment	$ 2,790,774	$ 2,792,872