Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues:
Natural gas sales	$ 99,100	$ 86,720	$ 125,774
Natural gas transportation	1,531,778	1,397,341	1,318,656
Natural gas storage	137,348	122,555	137,983
Other	6,779	9,519	10,106
Total operating revenues	1,775,005	1,616,135	1,592,519
Operating Costs and Expenses:
Cost of natural gas sales	99,100	86,720	125,774
Cost of natural gas transportation	19,589	19,689	26,501
Operation and maintenance	401,871	316,989	288,386
Administrative and general	182,121	168,759	179,489
Depreciation and amortization	318,058	307,707	277,850
Taxes - other than income taxes	65,612	60,119	49,567
Regulatory charge resulting from Tax Reform (Note 1)	471,096	0	0
Other expense, net	63,644	57,064	57,800
Total operating costs and expenses	1,621,091	1,017,047	1,005,367
Operating Income	153,914	599,088	587,152
Other (Income) and Other Expenses:
Interest expense - affiliate	60	60	64
Interest expense - other	158,814	151,234	82,774
Interest income - affiliate	(3,507)	(2,201)	(28)
Interest income - other	(2,782)	(2,185)	(1,933)
Allowance for equity and borrowed funds used during construction (AFUDC)	(92,013)	(68,964)	(63,072)
Equity in (earnings) loss of unconsolidated affiliates	6,188	(5,914)	(5,593)
Miscellaneous other (income) expenses, net	31,426	3,683	(517)
Total other (income) and other expenses	98,186	75,713	11,695
Net Income	55,728	523,375	575,457
Other comprehensive income:
Equity interest in unrealized gain on interest rate hedges (includes $103, $167, and $316 for the years ended December 31, 2017, 2016, and 2015, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses on interest rate hedges)	327	41	84
Comprehensive Income	$ 56,055	$ 523,416	$ 575,541