Business Combinations - Intangible Assets Acquired (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets, Gross [Abstract]
Aggregate Acquisitions	$ 12.8	$ 20.1
Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	5 years	6 years
Estimated Useful Life		6 years
Aggregate Acquisitions	$ 10.5	$ 16.8
Customer relationships \| Minimum
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	5 years
Customer relationships \| Maximum
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	6 years
Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	1 year	1 year
Aggregate Acquisitions	$ 1.5	$ 1.9
Customer backlog \| Minimum
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	1 year	3 months
Customer backlog \| Maximum
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	1 year 6 months	1 year
Non-compete agreements
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	5 years	5 years
Aggregate Acquisitions	$ 0.3	$ 0.7
Non-compete agreements \| Minimum
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	4 years	2 years
Non-compete agreements \| Maximum
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	5 years	5 years
Trade name
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	1 year	1 year
Estimated Useful Life	1 year	1 year
Aggregate Acquisitions	$ 0.1	$ 0.1
Developed software
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	3 years	4 years
Estimated Useful Life	3 years	4 years
Aggregate Acquisitions	$ 0.4	$ 0.6

Useful life of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

+ Details

Name:	prft_FiniteLivedIntangibleAssetAcquiredUsefulLife
Namespace Prefix:	prft_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

+ Details

Name:	us-gaap_FinitelivedIntangibleAssetsAcquired1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OrderOrProductionBacklogMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_NoncompeteAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TradeNamesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_SoftwareDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: