AMORTIZING INTANGIBLE ASSETS AND UNFAVORABLE GAS GATHERING CONTRACT (Tables)

12 Months Ended

Dec. 31, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets and liabilities subject to amortization

Details regarding our intangible assets and the unfavorable gas gathering contract (included in other noncurrent liabilities), all of which are subject to amortization, follow.

	December 31, 2015
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
		(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(9,534	)	$	14,661
Contract intangibles	12.5	426,464		(111,052		)	315,412
Rights-of-way	26.3	150,143		(18,906		)	131,237
Total intangible assets		$	600,802	$	(139,492	)	$	461,310
Unfavorable gas gathering contract	10.0	$	10,962	$	(6,077	)	$	4,885

	December 31, 2014
	Useful lives (In years)	Gross carrying amount		Accumulated amortization			Net
		(Dollars in thousands)
Favorable gas gathering contracts	18.7	$	24,195	$	(8,056	)	$	16,139
Contract intangibles	12.5	426,464		(75,713		)	350,751
Rights-of-way	27.0	135,435		(13,043		)	122,392
Total intangible assets		$	586,094	$	(96,812	)	$	489,282
Unfavorable gas gathering contract	10.0	$	10,962	$	(5,385	)	$	5,577

Recognized amortization expense in other revenues and cost and expenses

We recognized amortization expense in other revenues as follows:

	Year ended December 31,
	2015			2014			2013
	(In thousands)
Amortization expense – favorable gas gathering contracts	$	(1,478	)	$	(1,741	)	$	(2,078	)
Amortization expense – unfavorable gas gathering contract	692			797			1,046

We recognized amortization expense in costs and expenses as follows:

	Year ended December 31,
	2015		2014		2013
	(In thousands)
Amortization expense – contract intangibles	$	35,339	$	32,554	$	28,654
Amortization expense – rights-of-way	5,863		5,260		4,631

Estimated aggregate annual amortization expected to be recognized

The estimated aggregate annual amortization expected to be recognized as of December 31, 2015 for each of the five succeeding fiscal years follows.

	Intangible assets		Unfavorable gas gathering contract
	(In thousands)
2016	$	43,108	$	924
2017	41,959		1,047
2018	41,413		1,035
2019	41,659		1,045
2020	44,305		834