Contracts with Customers - Summary of Contract Assets and Contract Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Revenue from Contract with Customer [Abstract]
Contract assets	$ 970,128	$ 915,806
Contract liabilities	365,829	340,113
Net contract assets (liabilities)	604,299	$ 575,693
Change in contract assets	54,322
Change in contract liabilities	25,716
Change in contract assets and liabilities	$ 28,606
Percentage change in contract assets	5.90%
Percentage change in contract liabilities	7.60%
Percentage change in contract assets and liabilities	5.00%

Change in contract with customer assets.

No definition available.

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Period Type:	duration

- Definition

Change in contract with customer assets and liabilities net.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Change in contract with customer liability.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Contract with customer asset cumulative catchup adjustment to revenue change in measure of progress percent.

+ References

No definition available.

+ Details

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- Definition

Contract with customer asset liability cumulative catchup adjustment to revenue change in measure of progress percent.

+ References

No definition available.

+ Details

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Namespace Prefix:	psn_
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Balance Type:	na
Period Type:	duration

- Definition

Contract with customer asset and liabilities net.

+ References

No definition available.

+ Details

Name:	psn_ContractWithCustomerAssetLiabilityNet
Namespace Prefix:	psn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Contract with customer liability cumulative catchup adjustment to revenue change in measure of progress percent.

+ References

No definition available.

+ Details

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Namespace Prefix:	psn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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- Definition

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-2

+ Details

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

- References

No definition available.

+ Details

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