Transactions with Major Customers and Affiliates (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Puget Sound Energy, Inc. [Member]
Revenue, Major Customer [Line Items]
EntityWideRevenueMajorCustomerAmount	$ 100,799	$ 99,116	$ 95,564
Northwest Natural Gas Co. [Member]
Revenue, Major Customer [Line Items]
EntityWideRevenueMajorCustomerAmount	$ 47,297	$ 47,322	$ 48,022

Amount of revenue generated from a single external customer that accounts for 10 percent or more of an entity's revenues.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 280

-SubTopic 10

-Section 50

-Paragraph 42

-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 39

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Name:	us-gaap_EntityWideRevenueMajorCustomerAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration