Goodwill and other intangible assets

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

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 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


	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

Other amortizable intangible assets at December 31 were as follows:


	2020		2019
	(In thousands)
Customer relationships	$	28,836	$	17,958
Less accumulated amortization	6,887		6,268
	21,949		11,690
Noncompete agreements	3,941		3,439
Less accumulated amortization	2,309		1,957
	1,632		1,482
Other	12,927		8,094
Less accumulated amortization	11,012		6,020
	1,915		2,074
Total	$	25,496	$	15,246

The previous tables include goodwill and intangible assets associated with the business combinations completed during 2020 and 2019. For more information related to these business combinations, see Note 4.

Amortization expense for amortizable intangible assets for the years ended December 31, 2020, 2019 and 2018, was $9.0 million, $2.4 million and $1.2 million, respectively. The amounts of estimated amortization expense for identifiable intangible assets as of December 31, 2020, were:


	2021		2022		2023		2024		2025		Thereafter
	(In thousands)
Amortization expense	$	4,911	$	4,394	$	4,121	$	3,799	$	1,862	$	6,409