Dividends and Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands							3 Months Ended		6 Months Ended
	May 04, 2018	Feb. 21, 2018	Nov. 02, 2017	Aug. 02, 2017	May 05, 2017	Feb. 21, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Dividends and Earnings Per Share
Cash dividend declared (in dollars per share)	$ 0.060	$ 0.060	$ 0.060	$ 0.055	$ 0.055	$ 0.055	$ 0.060	$ 0.055	$ 0.120	$ 0.110
Numerator:
Net income attributable to Primoris							$ 11,715	$ 21,545	$ 12,403	$ 29,236
Denominator:
Weighted average shares for computation of basic earnings per share							51,531	51,437	51,505	51,515
Dilutive effect of shares issued to independent directors									3	3
Dilutive effect of restricted stock units							262	251	262	253
Weighted average shares for computation of diluted earnings per share							51,793	51,688	51,770	51,771
Earnings per share attributable to Primoris:
Basic earnings per share (in dollars per share)							$ 0.23	$ 0.42	$ 0.24	$ 0.57
Diluted earnings per share (in dollars per share)							$ 0.23	$ 0.42	$ 0.24	$ 0.56