Goodwill and other intangible assets

9 Months Ended

Sep. 30, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

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



Nine Months Ended September 30, 2018	Balance at January 1, 2018		Goodwill Acquired During the Year*		Balance at September 30, 2018
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	345,736
Construction materials and contracting	176,290		8,412		184,702
Construction services	109,765		—		109,765
Total	$	631,791	$	8,412	$	640,203


*	Relates to business acquisitions that occurred during the period, as discussed in Note 9.



Nine Months Ended September 30, 2017	Balance at January 1, 2017		Goodwill Acquired During the Year		Balance at September 30, 2017
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	345,736
Construction materials and contracting	176,290		—		176,290
Construction services	109,765		—		109,765
Total	$	631,791	$	—	$	631,791



Year Ended December 31, 2017	Balance at January 1, 2017		Goodwill Acquired During the Year		Balance at December 31, 2017
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	345,736
Construction materials and contracting	176,290		—		176,290
Construction services	109,765		—		109,765
Total	$	631,791	$	—	$	631,791

Other amortizable intangible assets were as follows:



	September 30, 2018		September 30, 2017		December 31, 2017
	(In thousands)
Customer relationships	$	15,920	$	15,248	$	15,248
Less accumulated amortization	13,342		13,176		13,382
	2,578		2,072		1,866
Noncompete agreements	2,606		2,430		2,430
Less accumulated amortization	1,911		1,769		1,805
	695		661		625
Other	6,458		7,020		6,990
Less accumulated amortization	5,413		5,544		5,644
	1,045		1,476		1,346
Total	$	4,318	$	4,209	$	3,837

Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2018, was $300,000 and $900,000, respectively. Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2017, was $500,000 and $1.7 million, respectively. Estimated amortization expense for amortizable intangible assets is $1.4 million in 2018, $1.2 million in 2019, $600,000 in 2020, $400,000 in 2021, $400,000 in 2022 and $1.2 million thereafter.