CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
OPERATING ACTIVITIES:
Net Income	$ 93,983	$ 98,406	$ 92,556
Items not affecting cash:
Depreciation	112,831	106,044	100,926
Amortization of debt issue costs, discount and deferred hedge gain	2,039	369	1,032
Amortization of nonvested shares	2,404	2,759	2,133
Equity portion of allowance for funds used during construction	(5,050)	(4,846)	(1,877)
(Gain) loss on disposition of assets	(721)	(332)	811
Deferred income taxes	54,617	51,890	64,065
Mountain States Transmission Intertie impairment	0	24,039	0
Gain on CELP arbitration decision	0	(47,894)	0
Changes in current assets and liabilities:
Restricted cash	(196)	6,016	146
Accounts receivable	(30,792)	3,456	(3,847)
Inventories	181	5,371	(8,831)
Other current assets	(2,940)	(1,856)	(3,551)
Accounts payable	6,235	10,976	(1,928)
Accrued expenses	1,949	14,149	1,883
Regulatory assets	(2,846)	(6,285)	1,684
Regulatory liabilities	(2,019)	15,241	16,020
Other noncurrent assets	(43,714)	(27,362)	(30,048)
Other noncurrent liabilities	7,755	1,052	2,583
Cash provided by operating activities	193,716	251,193	233,757
INVESTING ACTIVITIES:
Property, plant, and equipment additions	(230,454)	(219,234)	(188,730)
Asset acquisitions	(68,666)	(103,241)	0
Proceeds from sale of assets	3,766	262	209
Cash used in investing activities	(295,354)	(322,213)	(188,521)
FINANCING ACTIVITIES:
Dividends on common stock	(57,684)	(54,246)	(51,909)
Proceeds from issuance of common stock, net	56,825	28,477	0
Issuance of long-term debt	100,000	150,000	0
Repayment of long-term debt	(149)	(3,945)	(6,589)
Line of credit borrowings	0	0	80,000
Line of credit repayments	0	0	(233,000)
Issuances (repayments) of short-term borrowings, net	18,016	(44,000)	166,934
Treasury stock activity	(1,042)	(429)	153
Financing costs	(7,593)	(943)	(1,131)
Cash provided by (used in) financing activities	108,373	74,914	(45,542)
Increase (Decrease) in Cash and Cash Equivalents	6,735	3,894	(306)
Cash and Cash Equivalents, beginning of period	9,822	5,928	6,234
Cash and Cash Equivalents, end of period	$ 16,557	$ 9,822	$ 5,928