Note 15: 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 six month periods ended June 30, 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 from December 31, 2017 to June 30, 2018 are summarized below:



in thousands	Aggregates	Asphalt	Concrete	Calcium	Total
Goodwill
Total as of December 31, 2017	$ 3,030,688	$ 91,633	$ 0	$ 0	$ 3,122,321
Goodwill of acquired businesses 1	41,633	0	0	0	41,633
Total as of June 30, 2018	$ 3,072,321	$ 91,633	$ 0	$ 0	$ 3,163,954


1	See Note 16 for a summary of acquisitions.

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.