Condensed Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Revenues:
Natural gas sales	$ 26,763	$ 31,244	$ 74,867	$ 67,474
Natural gas transportation	389,080	346,004	1,116,891	1,042,547
Natural gas storage	33,954	34,258	102,778	88,315
Other	2,255	1,343	3,734	3,396
Total operating revenues	452,052	412,849	1,298,270	1,201,732
Operating Costs and Expenses:
Cost of natural gas sales	26,763	31,244	74,867	67,474
Cost of natural gas transportation	5,828	4,689	15,282	15,501
Operation and maintenance	113,101	83,916	267,914	225,975
Administrative and general	43,110	40,604	132,020	125,997
Depreciation and amortization	82,826	76,755	239,368	231,110
Taxes - other than income taxes	15,333	14,584	49,131	45,154
Other expense, net	13,475	12,894	43,112	41,541
Total operating costs and expenses	300,436	264,686	821,694	752,752
Operating Income	151,616	148,163	476,576	448,980
Other (Income) and Other Expenses:
Interest expense	41,304	37,318	115,797	113,957
Allowance for equity and borrowed funds used during construction (AFUDC)	(22,334)	(19,922)	(70,783)	(45,656)
Equity in earnings of unconsolidated affiliates	(912)	(1,455)	(3,322)	(4,447)
Miscellaneous other (income) expenses, net	(774)	309	(5,972)	655
Total other (income) and other expenses	17,284	16,250	35,720	64,509
Net Income	134,332	131,913	440,856	384,471
Other comprehensive income (loss):
Equity interest in unrealized gain (loss) on interest rate hedges (includes $38 and $41 for the three months ended and $ 75 and $140 for the nine months ended September 30, 2017 and September 30,2016, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses on interest rate hedges)	72	156	108	(128)
Comprehensive Income	$ 134,404	$ 132,069	$ 440,964	$ 384,343