Selected Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information
Revenue	$ 579,017	$ 608,311	$ 631,165	$ 561,502	$ 601,863	$ 507,828	$ 456,811	$ 430,446	$ 2,379,995	$ 1,996,948	$ 1,929,415
Gross Profit	68,477	70,421	84,483	55,053	68,616	50,129	43,285	39,277	278,434	201,307	219,873
Impairment of goodwill						2,716			0	2,716	401
Net income	23,808	22,134	22,396	8,512	14,766	4,756	5,287	2,916	76,850	27,725	37,151
Net income attributable to Primoris	$ 22,521	$ 20,597	$ 21,545	$ 7,691	$ 14,470	$ 4,504	$ 5,056	$ 2,693	$ 72,354	$ 26,723	$ 36,872
Earnings per share:
Basic earnings per share (in dollars per share)	$ 0.44	$ 0.40	$ 0.42	$ 0.15	$ 0.28	$ 0.09	$ 0.10	$ 0.05	$ 1.41	$ 0.52	$ 0.71
Diluted earnings per share (in dollars per share)	$ 0.44	$ 0.40	$ 0.42	$ 0.15	$ 0.28	$ 0.09	$ 0.10	$ 0.05	$ 1.40	$ 0.51	$ 0.71
Weighted average common shares outstanding:
Basic (in shares)	51,449	51,441	51,437	51,594	51,771	51,780	51,772	51,725	51,481	51,762	51,647
Diluted (in shares)	51,711	51,707	51,688	51,851	52,021	52,034	52,022	51,881	51,741	51,989	51,798