Goodwill and other intangible assets (Tables)

9 Months Ended

Sep. 30, 2018

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, 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

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