Goodwill and other intangible assets (Tables)

9 Months Ended

Sep. 30, 2016

Goodwill and Intangible Assets Disclosure [Abstract]

Changes in the carrying amount of goodwill

The changes in the carrying amount of goodwill were as follows:

Nine Months Ended September 30, 2016	Balance as of January 1, 2016		*	Goodwill Acquired During the Year		Balance as of September 30, 2016		*
	(In thousands)
Natural gas distribution	$	345,736		$	—	$	345,736
Pipeline and midstream	9,737			—		9,737
Construction materials and contracting	176,290			—		176,290
Construction services	103,441			6,323		109,764
Total	$	635,204		$	6,323	$	641,527

* Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods.

Nine Months Ended September 30, 2015	Balance as of January 1, 2015		*	Goodwill Acquired During the Year		Balance as of September 30, 2015		*
	(In thousands)
Natural gas distribution	$	345,736		$	—	$	345,736
Pipeline and midstream	9,737			—		9,737
Construction materials and contracting	176,290			—		176,290
Construction services	103,441			—		103,441
Total	$	635,204		$	—	$	635,204

* Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods.

Year Ended December 31, 2015	Balance as of January 1, 2015		*	Goodwill Acquired During the Year		Balance as of December 31, 2015		*
	(In thousands)
Natural gas distribution	$	345,736		$	—	$	345,736
Pipeline and midstream	9,737			—		9,737
Construction materials and contracting	176,290			—		176,290
Construction services	103,441			—		103,441
Total	$	635,204		$	—	$	635,204

* Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods.

Other amortizable intangible assets

Other amortizable intangible assets were as follows:

	September 30, 2016			September 30, 2015			December 31, 2015
	(In thousands)
Customer relationships	$	17,145		$	20,975		$	20,975
Accumulated amortization	(13,524		)	(16,455		)	(16,845		)
	3,621			4,520			4,130
Noncompete agreements	2,430			4,409			4,409
Accumulated amortization	(1,622		)	(3,632		)	(3,655		)
	808			777			754
Other	7,764			8,300			8,304
Accumulated amortization	(5,664		)	(5,689		)	(5,846		)
	2,100			2,611			2,458
Total	$	6,529		$	7,908		$	7,342