Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pro forma results
Pro forma tax rate used in calculating taxes on income from continuing operations (as a percent)	40.00%	40.00%	40.00%	40.00%
Revenues	$ 641,592	$ 479,326	$ 1,218,734	$ 933,491
Income before provision for income taxes	37,224	10,362	51,372	16,942
Net income attributable to Primoris	$ 21,937	$ 6,101	$ 31,409	$ 9,893
Weighted average common shares outstanding:
Basic (in shares)	51,437	51,772	51,515	51,749
Diluted (in shares)	51,688	52,022	51,771	51,950
Earnings per share:
Basic (in dollars per share)	$ 0.43	$ 0.12	$ 0.61	$ 0.19
Diluted (in dollars per share)	$ 0.42	$ 0.12	$ 0.61	$ 0.19