Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pro forma results
Pro forma tax rate used in calculating taxes on income from continuing operations (as a percent)	28.00%	40.00%	28.00%	40.00%
Revenues	$ 774,018	$ 869,039	$ 1,479,118	$ 1,610,081
Income before provision for income taxes	14,641	37,156	15,447	35,426
Net income (loss) attributable to Primoris	$ 9,371	$ 21,896	$ 7,451	$ 20,732
Weighted average common shares outstanding:
Basic (in shares)	51,531	51,437	51,505	51,515
Diluted (in shares)	51,793	51,688	51,770	51,771
Earnings per share:
Basic (in dollars per share)	$ 0.18	$ 0.43	$ 0.14	$ 0.40
Diluted (in dollars per share)	$ 0.18	$ 0.42	$ 0.14	$ 0.40