Noncontrolling Interests (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($) item	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Noncontrolling Interests
Number of joint ventures | item	2								2
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
Net income attributable to noncontrolling interests									4,496	1,002	279
Tax effect on income recognized									28,433	21,146	23,946
Distributions to non-controlling interests											29
Cash	170,385				135,823				170,385	135,823
Accounts receivable	358,175				388,000				358,175	388,000
Costs and estimated earnings in excess of billings	160,092				138,618				160,092	138,618
Billings in excess of costs and estimated earnings	159,034				112,606				159,034	112,606
Other current liabilities	480,763				449,938				480,763	449,938
Accounts payable	140,943				168,110				140,943	168,110
Carlsbad
Noncontrolling Interests
Revenue									110,669	7,254	2,887
Net income attributable to noncontrolling interests									1,780	325	172
Tax effect on income recognized									0
Distributions to partners									0
Capital contributions									0
Cash	44,308				4,630				44,308	4,630
Accounts receivable	15,343								15,343
Costs and estimated earnings in excess of billings					124					124
Billings in excess of costs and estimated earnings	42,743				3,426				42,743	3,426
Accounts payable	12,352				286				12,352	286
Due to Primoris					46					46
Wilmington
Noncontrolling Interests
Revenue									31,638	19,781	1,364
Net income attributable to noncontrolling interests									2,716	677	48
Tax effect on income recognized									0
Distributions to partners									0
Capital contributions									0
Cash	15,948				2,415				15,948	2,415
Accounts receivable	598				4,242				598	4,242
Billings in excess of costs and estimated earnings	1,480				2,572				1,480	2,572
Accounts payable	759				602				759	602
Due to Primoris	7,428				2,035				7,428	2,035
Carlsbad and Wilmington
Noncontrolling Interests
Cash	60,256				7,045				60,256	7,045
Accounts receivable	15,941				4,242				15,941	4,242
Costs and estimated earnings in excess of billings					124					124
Billings in excess of costs and estimated earnings	44,223				5,998				44,223	5,998
Accounts payable	$ 13,111				$ 888				$ 13,111	888
Power
Noncontrolling Interests
Number of joint ventures | item	2								2
Revenue									$ 606,125	$ 478,653	$ 466,292