Benefit Plans Regulatory Asset (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ 134,943	$ 119,959
Postretirement pensions and other medical benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status of obligation	74,222	69,616
Accrued benefit cost	(6,904)	(6,827)
Amount to be recovered in future rates	67,318	62,789
Tax gross-up	46,315	43,199
Regulatory asset	$ 113,633	$ 105,988

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 9, 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant