Fair Value of Financial Instruments: (Details) (GSWC, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Level 2
Financial liabilities:
Long-term debt-GSWC	$ 425,443
Carrying Amount
Financial liabilities:
Long-term debt-GSWC	335,829	335,791
Fair Value
Financial liabilities:
Long-term debt-GSWC	$ 425,443	$ 456,792

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant