Summary of Significant Accounting Policies - Customer Concentration (Details) - Revenues. - Customer concentration - Top ten customers	12 Months Ended
Dec. 31, 2017 customer item
Customer concentration
Number of top customers \| customer	10
Number of calendar years in which top customers typically generate minimum specified percentage of revenue \| item	1
Minimum percentage of revenues generated by top ten customers	50.00%

Represents the number of top customers who typically generate revenue in excess of a specified percentage of total revenues for the entity and consist of a different group of customers in each year.

No definition available.

Name:	prim_ConcentrationRiskNumberOfTopCustomers
Namespace Prefix:	prim_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration