Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Pro forma results
Pro forma tax rate used in calculating taxes on income from continuing operations (as a percent)	28.00%	28.00%
Revenues	$ 908,902	$ 2,388,020
Income before provision for income taxes	45,521	61,917
Net income attributable to Primoris	$ 32,691	$ 40,826
Weighted average common shares outstanding:
Basic (in shares)	51,403	51,471
Diluted (in shares)	51,735	51,760
Earnings per share:
Basic (in dollars per share)	$ 0.64	$ 0.79
Diluted (in dollars per share)	$ 0.63	$ 0.79

No definition available.

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- Definition

Represents the pro forma tax rate used in calculating taxes on income from continuing operations for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

No definition available.

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- Definition

The pro forma number of diluted weighted average shares outstanding for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

No definition available.

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The pro forma number of basic weighted average shares outstanding for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

No definition available.

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- Definition

The pro forma income from continuing operations before income taxes for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

No definition available.

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- Definition

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(3)
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-Publisher FASB
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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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