Mortgage Loan Participation and Sale Agreements - Summary of Mortgage Loan Participation and Sale Agreements (Detail) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
At period end:
Mortgage loan participation and sale agreements, At year end	$ 25,917,000	$ 0
Mortgage Loan Participation and Sale Agreement [Member]
Mortgage Loan Participation And Sale Agreement [Line Items]
Weighted-average interest rate	1.74%	1.62%	1.42%
Average balance	$ 70,391,000	$ 49,318,000	$ 44,770,000
Total interest expense	1,376,000	1,001,000	912,000
Maximum daily amount outstanding	99,469,000	148,032,000	$ 116,363,000
At period end:
Amount outstanding	25,917,000	0
Unamortized debt issuance costs	0	0
Mortgage loan participation and sale agreements, At year end	$ 25,917,000	$ 0
Weighted-average interest rate	2.02%	0.00%
Mortgage loans acquired for sale pledged to secure mortgage loan participation and sale agreements	$ 26,738,000	$ 0

Borrowings secured by mortgage loans held for sale in the form of a mortgage loan participation and sale agreement.

No definition available.

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Namespace Prefix:	pmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Mortgage Loan Participation And Sale Agreement [Line Items]

+ References

No definition available.

+ Details

Name:	pmt_MortgageLoanParticipationAndSaleAgreementLineItems
Namespace Prefix:	pmt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Participating mortgage loans average balance.

+ References

No definition available.

+ Details

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Namespace Prefix:	pmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents interest expense relating to the sale of mortgage loan participation agreements. Participation certificates represent an undivided beneficial ownership interests in pools of mortgage loans that have been pooled with government-sponsored agencies and, are sold to a lender pending the securitization of such mortgage loans and the sale of the resulting security. A commitment between the company and a non-affiliate to sell such security is also assigned to the lender at the time a participation certificate is sold.

+ References

No definition available.

+ Details

Name:	pmt_ParticipatingMortgageLoansInterestExpense
Namespace Prefix:	pmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Participating mortgage loans maximum daily outstanding.

+ References

No definition available.

+ Details

Name:	pmt_ParticipatingMortgageLoansMaximumDailyOutstanding
Namespace Prefix:	pmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Participating mortgage loans weighted average interest rate.

+ References

No definition available.

+ Details

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Namespace Prefix:	pmt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period end.

+ References

No definition available.

+ Details

Name:	pmt_PeriodEndAbstract
Namespace Prefix:	pmt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The stated interest rate on the mortgage loan receivable or the weighted average interest rate on a group of loans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
-Section S99
-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule IV)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

+ Details

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

- Definition

The aggregate amount of the participating mortgage obligation at the end of the accounting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=29639217&loc=d3e10013-112621

+ Details

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

- Definition

Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

+ Details

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

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	debit
Period Type:	instant

- Details

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