Dividends and Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands									3 Months Ended		9 Months Ended
	Nov. 02, 2017	Aug. 02, 2017	May 05, 2017	Mar. 21, 2017	Nov. 02, 2016	Aug. 03, 2016	May 02, 2016	Feb. 22, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Dividends and Earnings Per Share
Cash dividend declared (in dollars per share)	$ 0.060	$ 0.055	$ 0.055	$ 0.055	$ 0.055	$ 0.055	$ 0.055	$ 0.055	$ 0.055	$ 0.055	$ 0.17	$ 0.17
Numerator:
Net income attributable to Primoris									$ 20,597	$ 4,504	$ 49,833	$ 12,253
Denominator (shares in thousands):
Weighted average shares for computation of basic earnings per share									51,441	51,780	51,491	51,759
Dilutive effect of shares issued to independent directors									4	4	4	4
Dilutive effect of restricted stock units									262	250	256	215
Weighted average shares for computation of diluted earnings per share									51,707	52,034	51,751	51,978
Earnings per share attributable to Primoris:
Basic earnings per share (in dollars per share)									$ 0.40	$ 0.09	$ 0.97	$ 0.24
Diluted earnings per share (in dollars per share)									$ 0.40	$ 0.09	$ 0.96	$ 0.24