Consolidated Statements of Cash Flow (Parenthetical) (USD $) In Thousands	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010
Cash flows from investing activities:
Allowance for funds used during construction	$ 3,909	$ 3,002

Name:

us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract

Namespace Prefix:

us-gaap

Data Type:

xbrli:stringItemType

Balance Type:

na

Period Type:

duration