Goodwill and other intangible assets

6 Months Ended

Jun. 30, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and other intangible assets

Goodwill and other intangible assets

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

	Balance at January 1, 2020		Goodwill Acquired During the Year		Measurement Period Adjustments		Balance at June 30, 2020
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	—	$	345,736
Construction materials and contracting	217,234		6,483		—		223,717
Construction services	118,388		24,436		(3,613)		139,211
Total	$	681,358	$	30,919	$	(3,613)	$	708,664

	Balance at January 1, 2019		Goodwill Acquired During the Year		Measurement Period Adjustments		Balance at June 30, 2019
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	—	$	345,736
Construction materials and contracting	209,421		14,473		—		223,894
Construction services	109,765		—		—		109,765
Total	$	664,922	$	14,473	$	—	$	679,395

	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

During 2020 and 2019, the Company completed two and three 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 June 30, 2020 and 2019, and December 31, 2019, respectively, and increased the construction services segment's goodwill balance at June 30, 2020 and December 31, 2019, respectively, as noted in the previous tables. As a result of the business combinations, other intangible assets increased $21.0 million at June 30, 2020, compared to December 31, 2019. For more information related to these business combinations, see Note 9.

Other amortizable intangible assets were as follows:

	June 30, 2020		June 30, 2019		December 31, 2019
	(In thousands)
Customer relationships	$	30,087	$	14,601	$	17,958
Less accumulated amortization	5,239		5,629		6,268
	24,848		8,972		11,690
Noncompete agreements	4,229		3,179		3,439
Less accumulated amortization	2,084		1,798		1,957
	2,145		1,381		1,482
Other	13,060		6,578		8,094
Less accumulated amortization	8,538		5,608		6,020
	4,522		970		2,074
Total	$	31,515	$	11,323	$	15,246

Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2020, was $2.7 million and $4.7 million, respectively. Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2019, was $500,000 and $1.1 million, respectively. Estimated amortization expense for identifiable intangible assets as of June 30, 2020, was:

	Remainder of 2020		2021		2022		2023		2024		Thereafter
	(In thousands)
Amortization expense	$	5,313	$	5,199	$	4,711	$	4,490	$	4,160	$	7,642