Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pro forma results
Pro forma tax rate used in calculating taxes on income from continuing operations (as a percent)	36.50%	44.20%	36.50%	44.20%
Revenues	$ 608,311	$ 533,609	$ 1,827,045	$ 1,441,319
Income before provision for income taxes	32,086	12,977	83,458	24,752
Net income attributable to Primoris	$ 20,597	$ 6,816	$ 52,068	$ 13,675
Weighted average common shares outstanding:
Basic (in shares)	51,441	51,780	51,491	51,759
Diluted (in shares)	51,707	52,034	51,751	51,978
Earnings per share:
Basic (in dollars per share)	$ 0.40	$ 0.13	$ 1.01	$ 0.26
Diluted (in dollars per share)	$ 0.40	$ 0.13	$ 1.01	$ 0.26