Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
OPERATING ACTIVITIES:
Net income	$ 136,723	$ 152,813	$ 149,527
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation	93,419	90,486	87,915
Regulatory credits	(494)	(1,023)	(1,662)
Loss on sale of property, plant and equipment	0	6	0
Amortization of deferred charges and credits	1,578	1,491	2,293
Allowance for equity funds used during construction	(1,564)	(1,438)	(1,947)
Changes in current assets and liabilities:
Trade and other accounts receivable	(8,291)	270	1,927
Affiliated receivables	567	(132)	2,396
Exchange gas due from others	(1,262)	402	1,262
Materials and supplies	351	1,231	(1,759)
Other current assets	116	(54)	826
Trade accounts payable	6,305	(597)	(559)
Affiliated payables	2,100	(1,462)	(13,026)
Exchange gas due to others	1,262	(402)	(1,262)
Other accrued liabilities	169	827	985
Changes in noncurrent assets and liabilities:
Deferred charges	(4,015)	(2,829)	(5,865)
Other deferred credits	5,442	4,769	8,148
Net cash provided by operating activities	232,406	244,358	229,199
FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	0	0	8,000
Retirement of long-term debt	0	0	(8,000)
Capital contributions from parent	8,630	5,100	19,000
Distributions paid	(137,500)	(127,000)	(191,450)
Other	329	657	(1,209)
Net cash used in financing activities	(128,541)	(121,243)	(173,659)
Property, plant and equipment -
Capital expenditures	(134,330)	(115,111)	(120,236)
Proceeds from sales	7,843	(993)	3,913
Repayments from (advances to) affiliates	22,702	(6,979)	60,386
Net cash used in investing activities	(103,785)	(123,083)	(55,937)
NET INCREASE (DECREASE) IN CASH	80	32	(397)
CASH AT BEGINNING OF PERIOD	37	5	402
CASH AT END OF PERIOD	$ 117	$ 37	$ 5