Dividends and Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands													3 Months Ended								12 Months Ended
	Oct. 31, 2019	Aug. 02, 2019	May 03, 2019	Feb. 26, 2019	Nov. 02, 2018	Aug. 02, 2018	May 04, 2018	Feb. 21, 2018	Nov. 02, 2017	Aug. 02, 2017	May 05, 2017	Feb. 21, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share
Cash dividend declared (in dollars per share)	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.060	$ 0.055	$ 0.055	$ 0.055									$ 0.240	$ 0.240	$ 0.225
Numerator:
Net income													$ 27,511	$ 35,826	$ 17,824	$ 2,936	$ 34,381	$ 34,805	$ 14,191	$ 4,216	$ 84,097	$ 87,593	$ 76,850
Net income attributable to noncontrolling interests																					(1,770)	(10,132)	(4,496)
Net income attributable to Primoris													$ 26,945	$ 35,648	$ 17,787	$ 1,947	$ 32,367	$ 32,691	$ 11,715	$ 688	$ 82,327	$ 77,461	$ 72,354
Denominator:
Weighted average shares for computation of basic earnings per share													50,478	50,976	50,912	50,770	50,993	51,403	51,531	51,479	50,784	51,350	51,481
Dilutive effect of shares issued to independent directors																					3	3	3
Dilutive effect of restricted stock units																					297	317	257
Weighted average shares for computation of diluted earnings per share													50,711	51,215	51,228	51,188	51,397	51,735	51,793	51,747	51,084	51,670	51,741
Earnings per share attributable to Primoris:
Basic earnings per share (in dollars per share)													$ 0.53	$ 0.70	$ 0.35	$ 0.04	$ 0.63	$ 0.64	$ 0.23	$ 0.01	$ 1.62	$ 1.51	$ 1.41
Diluted earnings per share (in dollars per share)													$ 0.53	$ 0.70	$ 0.35	$ 0.04	$ 0.63	$ 0.63	$ 0.23	$ 0.01	$ 1.61	$ 1.50	$ 1.40