Goodwill and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Changes in the carrying amount of goodwill

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

Other amortizable intangible assets

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

Estimated amortization expense

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