Stockholders' Equity (Details) (USD $)	1 Months Ended						2 Months Ended	8 Months Ended	12 Months Ended			1 Months Ended	0 Months Ended	1 Months Ended
	Aug. 31, 2014	Feb. 28, 2014	Aug. 31, 2013	Mar. 31, 2013	Aug. 31, 2012	Feb. 29, 2012	Jun. 30, 2012	Sep. 30, 2014	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Jan. 07, 2013	Feb. 28, 2013	May 31, 2012
Common Stock
Common stock, authorized (in shares)									90,000,000	90,000,000
Par value of common stock (in dollars per share)									$ 0.0001	$ 0.0001
Common stock issued (in shares)									51,561,396	51,571,394
Common stock outstanding (in shares)									51,561,396	51,571,394
Number of holders of common stock									364
Cash received from issuance of common stock as part of the company's Plan for managers and executives									$ 1,671,000	$ 1,455,000	$ 1,240,000
Discounted price from market price at which shares purchased by participants in LTR Plan (as a percent)									25.00%	25.00%
Shares of common stock issued as a part of quarterly compensation of non-employee members of the Board of Directors	6,172	6,375	9,110	12,480	15,280	12,395			12,547	21,590
Period of restriction on trade for shares issued to non-employee members of the board of directors under the Primoris Long-term Retention Plan									1 year
Aggregate purchase price up to which shares can be acquired under share repurchase program		23,000,000													20,000,000
Number of shares purchased and cancelled under the share repurchase program							89,600	100,000
Amount paid for shares purchased and cancelled under share repurchase program							1,000,000	2,800,000
Average cost of repurchased shares of stock (in dollars per share)							$ 11.17	$ 28.44
Preferred Stock
Preferred stock, authorized (in shares)									1,000,000	1,000,000
Par value of preferred stock (in dollars per share)									$ 0.0001	$ 0.0001
Preferred stock, shares outstanding									0	0
Warrants
Warrants outstanding (in shares)									0	0
Ecuador business
Common Stock
Price of shares issued (in dollars per share)				19.81
Shares provided for the payment of note receivable				15,144
Notes receivable				300,000
LTR Plan
Common Stock
Amount received in exchange for shares of common stock under a long term incentive plan				1,455,000								1,671,000
Shares of common stock purchased under the long-term incentive plan				131,989								77,455
Discounted price from market price at which shares purchased by participants in LTR Plan (as a percent)												75.00%
Equity Plan
Common Stock
Shares of common stock purchased under the long-term incentive plan									77,455	131,989
Shares of common stock reserved for issuance upon exercise of all future stock option grants, SARS and grants of restricted shares under the 2013 Equity Plan										2,278,651
Equity Plan | Restricted Stock Units
Common Stock
Shares of common stock reserved for issuance upon exercise of all future stock option grants, SARS and grants of restricted shares under the 2013 Equity Plan									2,278,651
Q3 Contracting
Common Stock
Stock issued to sellers (in shares)										29,273			29,273	29,273
Price of shares issued (in dollars per share)													$ 14.69
Stock issued for acquisition													$ 430,000