Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income	$ 9,024	$ 27,390	$ 16,003	$ 11,265	$ 25,554	$ 23,193	$ 15,893	$ 10,040	$ 17,932	$ 17,948	$ 11,857	$ 10,530	$ 63,682	$ 74,680	$ 58,267
Net income attributable to noncontrolling interests													(526)	(5,020)	(1,511)
Net income attributable to Primoris	$ 8,930	$ 27,390	$ 16,003	$ 10,833	$ 22,481	$ 21,845	$ 15,564	$ 9,770	$ 17,021	$ 17,516	$ 11,733	$ 10,486	$ 63,156	$ 69,660	$ 56,756
Denominator:
Weighted average shares for computation of basic earnings per share	51,561	51,606	51,655	51,610	51,571	51,568	51,562	51,456	51,404	51,398	51,435	51,096	51,607	51,540	51,391
Dilutive effect of shares issued to independent directors													2	3	11
Dilutive effect of unvested restricted stock units													138	66
Dilutive effect of shares to be issued to Q3C sellers														1	4
Weighted average shares for computation of diluted earnings per share	51,710	51,759	51,804	51,714	51,671	51,671	51,626	51,467	51,418	51,404	51,435	51,337	51,747	51,610	51,406
Earnings per share attributable to Primoris:
Basic (in dollars per share)	$ 0.17	$ 0.53	$ 0.31	$ 0.21	$ 0.44	$ 0.42	$ 0.30	$ 0.19	$ 0.33	$ 0.34	$ 0.23	$ 0.21	$ 1.22	$ 1.35	$ 1.10
Diluted (in dollars per share)	$ 0.17	$ 0.53	$ 0.31	$ 0.21	$ 0.44	$ 0.42	$ 0.30	$ 0.19	$ 0.33	$ 0.34	$ 0.23	$ 0.20	$ 1.22	$ 1.35	$ 1.10