STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Interest charges and financing costs
Other financing costs	$ 765	$ 659	$ 1,425	$ 1,309

Represents the charge against earnings during the period for commitment fees and debt issuance expenses.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 5
-Section 03
-Paragraph 8

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Name:	us-gaap_DebtRelatedCommitmentFeesAndDebtIssuanceCosts
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration