Acquired identifiable intangible assets are classified into three categories: (1) goodwill, (2) intangible assets with finite lives subject to amortization and (3) intangible assets with indefinite lives. Goodwill and intangible assets with indefinite lives are not amortized; rather, they are reviewed for impairment at least annually. For additional information about our policies on impairment reviews, see Note 1 under the captions Goodwill Impairment and Impairment of Long-lived Assets excluding Goodwill.

Goodwill is recognized when the consideration paid for a business exceeds the fair value of the tangible and identifiable intangible assets acquired. Goodwill is allocated to reporting units for purposes of testing goodwill for impairment. There were no charges for goodwill impairment in the years ended December 31, 2019, 2018 and 2017. Accumulated goodwill impairment losses amount to $252,664,000 in the Calcium segment.

We have four reportable segments organized around our principal product lines: Aggregates, Asphalt, Concrete and Calcium. Changes in the carrying amount of goodwill by reportable segment for the three years ended December 31, 2019 are as follows:



in thousands	Aggregates	Asphalt	Concrete	Calcium	Total
Goodwill
Totals at December 31, 2017	$ 3,030,688	$ 91,633	$ 0	$ 0	$ 3,122,321
Goodwill of acquired businesses ¹	43,075	0	0	0	43,075
Totals at December 31, 2018	$ 3,073,763	$ 91,633	$ 0	$ 0	$ 3,165,396
Goodwill of acquired businesses ¹	1,665	0	0	0	1,665
Totals at December 31, 2019	$ 3,075,428	$ 91,633	$ 0	$ 0	$ 3,167,061

We test goodwill for impairment on an annual basis or more frequently if events or circumstances change in a manner that would more likely than not reduce the fair value of a reporting unit below its carrying value. A decrease in the estimated fair value of one or more of our reporting units could result in the recognition of a material, noncash write-down of goodwill.

Intangible assets acquired in business combinations are stated at their fair value determined as of the date of acquisition. Costs incurred to renew or extend the life of existing intangible assets are capitalized. These capitalized renewal/extension costs were immaterial for the years presented. Intangible assets consist of contractual rights in place (primarily permitting and zoning rights), noncompetition agreements, customer relationships and trade names and trademarks. Intangible assets acquired individually or otherwise obtained outside a business combination consist primarily of permitting, permitting compliance and zoning rights and are stated at their historical cost less accumulated amortization.

See Note 19 for the details of the intangible assets acquired in business acquisitions during 2019, 2018 and 2017. Amortization of finite-lived intangible assets is computed based on the estimated life of the intangible assets. Contractual rights in place associated with aggregates reserves are amortized using the unit-of-sales method based on estimated recoverable units. Other intangible assets are amortized principally by the straight-line method. Intangible assets are reviewed for impairment when events or circumstances indicate that the carrying amount may not be recoverable. There were no charges for impairment of intangible assets in 2019, 2018 and 2017.

The gross carrying amount and accumulated amortization by major intangible asset class for the years ended December 31 are summarized below:



in thousands	2019	2018
Gross Carrying Amount
Contractual rights in place	$ 1,132,958	$ 1,107,838
Noncompetition agreements	7,667	7,667
Permitting, permitting compliance and zoning rights	136,646	126,538
Other ¹	11,951	13,996
Total gross carrying amount	$ 1,289,222	$ 1,256,039
Accumulated Amortization
Contractual rights in place	$ (155,555)	$ (122,100)
Noncompetition agreements	(6,126)	(4,212)
Permitting, permitting compliance and zoning rights	(30,545)	(27,464)
Other ¹	(5,521)	(6,885)
Total accumulated amortization	$ (197,747)	$ (160,661)
Total Intangible Assets Subject to Amortization, net	$ 1,091,475	$ 1,095,378
Intangible Assets with Indefinite Lives	0	0
Total Intangible Assets, net	$ 1,091,475	$ 1,095,378
Amortization Expense for the Year	$ 40,541	$ 34,924

Estimated amortization expense for the five years subsequent to December 31, 2019 is as follows: