Dividends and Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands									3 Months Ended								12 Months Ended
	Nov. 02, 2017	Aug. 02, 2017	May 05, 2017	Feb. 21, 2017	Nov. 02, 2016	Aug. 03, 2016	May 02, 2016	Feb. 22, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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									$ 0.225	$ 0.220	$ 0.205
Numerator:
Net income									$ 23,808	$ 22,134	$ 22,396	$ 8,512	$ 14,766	$ 4,756	$ 5,287	$ 2,916	$ 76,850	$ 27,725	$ 37,151
Net income attributable to noncontrolling interests																	(4,496)	(1,002)	(279)
Net income attributable to Primoris									$ 22,521	$ 20,597	$ 21,545	$ 7,691	$ 14,470	$ 4,504	$ 5,056	$ 2,693	$ 72,354	$ 26,723	$ 36,872
Denominator (shares in thousands):
Weighted average shares for computation of basic earnings per share									51,449	51,441	51,437	51,594	51,771	51,780	51,772	51,725	51,481	51,762	51,647
Dilutive effect of shares issued to independent directors																	3	3	2
Dilutive effect of restricted stock units																	257	224	149
Weighted average shares for computation of diluted earnings per share									51,711	51,707	51,688	51,851	52,021	52,034	52,022	51,881	51,741	51,989	51,798
Earnings per share attributable to Primoris:
Basic earnings per share (in dollars per share)									$ 0.44	$ 0.40	$ 0.42	$ 0.15	$ 0.28	$ 0.09	$ 0.10	$ 0.05	$ 1.41	$ 0.52	$ 0.71
Diluted earnings per share (in dollars per share)									$ 0.44	$ 0.40	$ 0.42	$ 0.15	$ 0.28	$ 0.09	$ 0.10	$ 0.05	$ 1.40	$ 0.51	$ 0.71