Summary of Significant Accounting Policies, Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Regulated utility plants	$ 3,792,113	$ 3,759,541
Other	267,342	264,114
Property, plant and equipment	4,059,455	4,023,655
Accumulated depreciation	(1,273,802)	(1,230,783)
Net property, plant and equipment	$ 2,785,653	$ 2,792,872