Goodwill and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Changes in the carrying amount of goodwill

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

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

Estimated amortization expense

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