Represents the number of properties the Company is leasing.

No definition available.

Name:	prim_NumberOfLeasedProperties
Namespace Prefix:	prim_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of mortgages assumed.

+ References

No definition available.

+ Details

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

- Definition

Amount of liabilities assumed at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of acquisition of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

Name:	us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=prim_StockdaleInvestmentGroupIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Party Transactions (Details) $ in Millions	1 Months Ended	6 Months Ended		12 Months Ended
Related Party Transactions (Details) $ in Millions	Mar. 31, 2017 USD ($) loan	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) loan	Feb. 28, 2017 item
Mortgages
Related party transactions
Number of mortgages assumed \| loan				3
Assumed notes				$ 4.2
SIGI
Related party transactions
Number of leased properties \| item					3
Purchase of properties	$ 12.8
Lease payments to related party		$ 0.0	$ 0.2
SIGI \| Mortgages
Related party transactions
Number of mortgages assumed \| loan	3
Assumed notes	$ 4.2