Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Revenues:
Natural gas sales	$ 125,774	$ 121,397	$ 113,488
Natural gas transportation	1,318,656	1,166,244	1,094,807
Natural gas storage	137,983	140,344	143,047
Other	10,106	5,152	4,990
Total operating revenues	1,592,519	1,433,137	1,356,332
Operating Costs and Expenses:
Cost of natural gas sales	125,774	121,397	113,488
Cost of natural gas transportation	26,501	31,629	24,936
Operation and maintenance	288,386	271,603	264,631
Administrative and general	179,489	183,760	182,352
Depreciation and amortization	277,850	270,181	265,273
Taxes - other than income taxes	49,567	44,521	43,898
Other expense, net	57,800	37,208	32,606
Total operating costs and expenses	1,005,367	960,299	927,184
Operating Income	587,152	472,838	429,148
Other (Income) and Other Expenses:
Interest expense - affiliate	64	70	190
Interest expense - other	82,774	84,917	84,000
Interest income - affiliate	(28)	(49)	(45)
Interest income - other	(1,933)	(1,782)	(2,068)
Allowance for equity and borrowed funds used during construction (AFUDC)	(63,072)	(25,046)	(18,595)
Equity in earnings of unconsolidated affiliates	(5,593)	(5,783)	(5,678)
Miscellaneous other (income) expenses, net	(517)	(2,373)	(2,682)
Total other (income) and other expenses	11,695	49,954	55,122
Net Income	575,457	422,884	374,026
Other comprehensive income:
Equity interest in unrealized gain on interest rate hedges (includes S316, $344, and $330 for the years ended December 31, 2015, 2014, and 2013, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses on interest rate hedges)	84	143	464
Comprehensive Income	$ 575,541	$ 423,027	$ 374,490