Goodwill and other intangible assets

6 Months Ended

Jun. 30, 2021

Goodwill and Intangible Assets Disclosure [Abstract]

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


	Balance at January 1, 2021		Goodwill Acquired During the Year		Measurement Period Adjustments		Balance at June 30, 2021
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	—	$	345,736
Construction materials and contracting	226,003		2,900		—		228,903
Construction services	143,224		—		—		143,224
Total	$	714,963	$	2,900	$	—	$	717,863


	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, 2020		Goodwill Acquired During the Year		Measurement Period Adjustments		Balance at December 31, 2020
	(In thousands)
Natural gas distribution	$	345,736	$	—	$	—	$	345,736
Construction materials and contracting	217,234		8,778		(9)		226,003
Construction services	118,388		24,436		400		143,224
Total	$	681,358	$	33,214	$	391	$	714,963

Other amortizable intangible assets were as follows:


	June 30, 2021		June 30, 2020		December 31, 2020
	(In thousands)
Customer relationships	$	29,423	$	30,087	$	28,836
Less accumulated amortization	8,765		5,239		6,887
	20,658		24,848		21,949
Noncompete agreements	3,991		4,229		3,941
Less accumulated amortization	2,576		2,084		2,309
	1,415		2,145		1,632
Other	11,957		13,060		12,927
Less accumulated amortization	10,629		8,538		11,012
	1,328		4,522		1,915
Total	$	23,401	$	31,515	$	25,496

The previous tables include goodwill and intangible assets associated with the business combinations completed during 2021 and 2020. For more information related to these business combinations, see Note 10.

Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2021, was $1.2 million and $2.7 million, respectively. 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. Estimated amortization expense for identifiable intangible assets as of June 30, 2021, was:


	Remainder of 2021		2022		2023		2024		2025		Thereafter
	(In thousands)
Amortization expense	$	2,381	$	4,678	$	4,329	$	3,957	$	2,060	$	5,996