Dividends and Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands								3 Months Ended		9 Months Ended
	Aug. 02, 2018	May 04, 2018	Feb. 21, 2018	Nov. 02, 2017	Aug. 02, 2017	May 05, 2017	Feb. 21, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Dividends and Earnings Per Share
Cash dividend declared (in dollars per share)	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.055	$ 0.055	$ 0.055	$ 0.060	$ 0.055	$ 0.180	$ 0.170
Numerator:
Net income attributable to Primoris								$ 32,691	$ 20,597	$ 45,094	$ 49,833
Denominator:
Weighted average shares for computation of basic earnings per share								51,403	51,441	51,471	51,491
Dilutive effect of shares issued to independent directors								4	4	3	4
Dilutive effect of restricted stock units								328	262	286	256
Weighted average shares for computation of diluted earnings per share								51,735	51,707	51,760	51,751
Earnings per share attributable to Primoris:
Basic earnings per share (in dollars per share)								$ 0.64	$ 0.40	$ 0.88	$ 0.97
Diluted earnings per share (in dollars per share)								$ 0.63	$ 0.40	$ 0.87	$ 0.96