Business Combinations (Details 6) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		0 Months Ended	9 Months Ended				0 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended		1 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 12, 2012 Sprint	Sep. 30, 2013 Sprint	Sep. 30, 2012 Sprint	Sep. 30, 2012 Silva	Sep. 30, 2012 Saxon	Mar. 11, 2013 FSSI	Jun. 30, 2013 FSSI	Sep. 30, 2013 FSSI	Jan. 07, 2013 Q3C	Nov. 17, 2012 Q3C	Aug. 31, 2013 Q3C	Sep. 30, 2013 Q3C
Business combinations
Cash paid for acquisitions			$ 2,273	$ 38,110	$ 21,197		$ 21,197	$ 13,934	$ 2,979	$ 1,025	$ 650	$ 1,675		$ 48,116	$ 598	$ 598
Pro forma results
Pro forma tax rate used in calculating taxes on income from continuing operations (as a percent)	39.00%	39.00%	39.00%	39.00%
Unregistered shares of common stock issued with an acquisition					62,052	62,052							29,273			29,273
Revenues	551,333	476,570	1,409,140	1,192,167
Income before provision for income taxes	37,268	31,967	79,283	65,395
Net income attributable to Primoris	$ 21,845	$ 19,379	$ 47,109	$ 39,848
Weighted average common shares outstanding:
Basic (in shares)	51,568	51,427	51,530	51,433
Diluted (in shares)	51,671	51,433	51,594	51,448
Earnings per share:
Basic (in dollars per share)	$ 0.42	$ 0.38	$ 0.91	$ 0.77
Diluted (in dollars per share)	$ 0.42	$ 0.38	$ 0.91	$ 0.77