Number of customers representing ten percent or more of accounts receivable.

No definition available.

Name:	psn_NumberOfCustomersRepresentingTenPercentOrMoreOfAccountsReceivable
Namespace Prefix:	psn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of customers representing ten percent or more of revenues.

+ References

No definition available.

+ Details

Name:	psn_NumberOfCustomersRepresentingTenPercentOrMoreOfRevenues
Namespace Prefix:	psn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue performance obligation payment terms.

+ References

No definition available.

+ Details

Name:	psn_RevenuePerformanceObligationPaymentTerms
Namespace Prefix:	psn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Significant Accounting Policies [Line Items]

+ References

No definition available.

+ Details

Name:	psn_SignificantAccountingPoliciesLineItems
Namespace Prefix:	psn_
Data Type:	xbrli:stringItemType
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

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

+ Details

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

- Definition

An entity will typically disclose the amount of any repurchase obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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

- Definition

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPSharesContributedToESOP
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleEffectOfAdoptionQuantification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cumulative amount of the reporting entity's undistributed earnings or deficit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(a)(4))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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

- Definition

Number of previously issued common shares repurchased by the issuing entity and held in treasury.

+ References

+ Details

Name:	us-gaap_TreasuryStockCommonShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201409Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis=us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=psn_ContractWithCustomerAssetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=psn_DeferredTaxAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=psn_ContractWithCustomerLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=psn_NonControllingInterestsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=psn_NetDeferredTaxAssetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=psn_DeferredTaxAssetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CreditConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
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:

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) Customer shares	Dec. 31, 2018 USD ($) shares	Dec. 29, 2017 USD ($) shares	Dec. 30, 2017 USD ($)
Significant Accounting Policies [Line Items]
Contributions to ESOP \| shares		1,345,198	1,874,988	1,790,496
Repurchase of shares of common stock from ESOP \| shares		191,331	5,553,891	5,843,211
Redemption value of ESOP participants interest		$ 6,300	$ 125,800	$ 111,400
Increase in retained earnings		(218,025)	12,445
ASC 606
Significant Accounting Policies [Line Items]
Adoption of ASC 606			$ (4,735)
ASC 606 \| Difference between Revenue Guidance in Effect before and after Topic 606
Significant Accounting Policies [Line Items]
Increase in retained earnings					$ 4,700
ASC 606 \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Increase to Contract Assets
Significant Accounting Policies [Line Items]
Cumulative effect adjustments					2,500
ASC 606 \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Increase to Deferred Tax Assets
Significant Accounting Policies [Line Items]
Cumulative effect adjustments					100
ASC 606 \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Increase to Contract Liabilities
Significant Accounting Policies [Line Items]
Cumulative effect adjustments					7,200
ASC 606 \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Increase to Non-controlling Interests
Significant Accounting Policies [Line Items]
Cumulative effect adjustments					$ 100
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Adoption of ASC 606		52,608
Accounting Standards Update 2016-02 \| Net Deferred Tax Asset
Significant Accounting Policies [Line Items]
Adoption of ASC 606		52,600
Accounting Standards Update 2016-02 \| Deferred Tax Asset
Significant Accounting Policies [Line Items]
Adoption of ASC 606	$ 700	$ 700
Concentration of Credit Risk
Significant Accounting Policies [Line Items]
Number of customers representing more than 10% of revenue \| Customer		0
Number of customers representing more than 10% of accounts receivable \| Customer		0
Revenue Benchmark \| Concentration of Credit Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		48.00%	42.00%	36.00%
Accounts Receivable \| Concentration of Credit Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		18.00%	29.00%
Minimum
Significant Accounting Policies [Line Items]
Performance obligations payment terms from date of invoice		30 days
Intangible assets useful lives of underlying assets		1 year
Maximum
Significant Accounting Policies [Line Items]
Performance obligations payment terms from date of invoice		120 days
Intangible assets useful lives of underlying assets		10 years