Goodwill and other intangible assets

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Other Intangible Assets

The changes in the carrying amount of goodwill for the year ended December 31, 2019, were as follows:



	Balance at January 1, 2019		Goodwill Acquired During the Year		Measurement Period Adjustments			Balance at December 31, 2019
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	—		$	345,736
Construction materials and contracting	209,421		14,482		(6,669		)	217,234
Construction services	109,765		8,623		—			118,388
Total	$	664,922	$	23,105	$	(6,669	)	$	681,358

The changes in the carrying amount of goodwill for the year ended December 31, 2018, were as follows:



	Balance at January 1, 2018		Goodwill Acquired During the Year		Measurement Period Adjustments		Balance at December 31, 2018
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	—	$	345,736
Construction materials and contracting	176,290		33,131		—		209,421
Construction services	109,765		—		—		109,765
Total	$	631,791	$	33,131	$	—	$	664,922

During 2019 and 2018, the Company completed three and four business combinations, respectively, and the results of these acquisitions have been included in the Company's construction materials and contracting and construction services segments. These business combinations increased the construction materials and contracting segment's goodwill balance at December 31, 2019 and 2018, respectively, and increased the construction services segment's goodwill balance at December 31, 2019, as noted in the previous tables. At December 31, 2019 and 2018, the impacts of these business combinations on other intangible assets resulted in an increase of $6.8 million and $8.2 million, respectively. For more information related to these business combinations, see Note 3.

Other amortizable intangible assets at December 31 were as follows:



	2019		2018
	(In thousands)
Customer relationships	$	17,958	$	22,720
Less accumulated amortization	6,268		13,535
	11,690		9,185
Noncompete agreements	3,439		2,605
Less accumulated amortization	1,957		1,956
	1,482		649
Other	8,094		6,458
Less accumulated amortization	6,020		5,477
	2,074		981
Total	$	15,246	$	10,815

Amortization expense for amortizable intangible assets for the years ended December 31, 2019, 2018 and 2017, was $2.4 million, $1.2 million and $2.0 million, respectively. The amounts of estimated amortization expense for identifiable intangible assets as of December 31, 2019, were:



	2020		2021		2022		2023		2024		Thereafter
	(In thousands)
Amortization expense	$	3,365	$	2,016	$	1,968	$	1,924	$	1,610	$	4,363