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Other intangible assets (Details 2) - USD ($) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible assets, net (excluding goodwill) | $ 11,323,000 | $ 4,190,000 | $ 11,323,000 | $ 4,190,000 | $ 10,815,000
Amortization of intangible assets | 500,000 | 300,000 | 1,100,000 | 700,000 |
Customer relationships |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible assets, gross | 14,601,000 | 15,587,000 | 14,601,000 | 15,587,000 | 22,720,000
Intangible assets, less accumulated amortization | 5,629,000 | 13,191,000 | 5,629,000 | 13,191,000 | 13,535,000
Intangible assets, net (excluding goodwill) | 8,972,000 | 2,396,000 | 8,972,000 | 2,396,000 | 9,185,000
Noncompete agreements |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible assets, gross | 3,179,000 | 2,546,000 | 3,179,000 | 2,546,000 | 2,605,000
Intangible assets, less accumulated amortization | 1,798,000 | 1,877,000 | 1,798,000 | 1,877,000 | 1,956,000
Intangible assets, net (excluding goodwill) | 1,381,000 | 669,000 | 1,381,000 | 669,000 | 649,000
Other intangible assets |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Intangible assets, gross | 6,578,000 | 6,458,000 | 6,578,000 | 6,458,000 | 6,458,000
Intangible assets, less accumulated amortization | 5,608,000 | 5,333,000 | 5,608,000 | 5,333,000 | 5,477,000
Intangible assets, net (excluding goodwill) | $ 970,000 | $ 1,125,000 | 970,000 | $ 1,125,000 | $ 981,000
Construction materials and contracting [Member] | Series of Individually Immaterial Business Acquisitions [Member] |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Finite-lived Intangible Assets Acquired |  |  | $ 1,600,000 |  |

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 + Details
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