Note 2 - Investments - Security Holdings in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less than 12 Months, fair value	$ 230,995	$ 354,769
Less than 12 Months, Accumulated Loss	(5,798)	(8,726)
12 Months or Longer, fair value	264,175	309,203
12 Months or Longer, Accumulated Loss	(20,897)	(28,531)
Fair value	495,170	663,972
Accumulated Loss	(26,695)	(37,257)
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less than 12 Months, fair value	7,152	16,507
Less than 12 Months, Accumulated Loss	(3)	(65)
12 Months or Longer, fair value	10,029	14,291
12 Months or Longer, Accumulated Loss	(345)	(584)
Fair value	17,181	30,798
Accumulated Loss	(348)	(649)
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less than 12 Months, fair value	7,358	2,614
Less than 12 Months, Accumulated Loss	(1,099)	(419)
12 Months or Longer, fair value	8,069	5,076
12 Months or Longer, Accumulated Loss	(419)	(438)
Fair value	15,427	7,690
Accumulated Loss	(1,518)	(857)
Special Revenue Excluding Asset Backed Securities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less than 12 Months, fair value	1,618	2,182
Less than 12 Months, Accumulated Loss	(99)	(426)
12 Months or Longer, fair value	14,481	21,733
12 Months or Longer, Accumulated Loss	(2,347)	(3,308)
Fair value	16,099	23,915
Accumulated Loss	(2,446)	(3,734)
Corporate Debt Securities and Other Debt Obligations [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less than 12 Months, fair value	111,899	181,179
Less than 12 Months, Accumulated Loss	(3,475)	(4,996)
12 Months or Longer, fair value	143,214	176,531
12 Months or Longer, Accumulated Loss	(8,388)	(13,353)
Fair value	255,113	357,710
Accumulated Loss	(11,863)	(18,349)
Asset-Backed Securities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
Less than 12 Months, fair value	102,968	152,287
Less than 12 Months, Accumulated Loss	(1,122)	(2,820)
12 Months or Longer, fair value	88,382	91,572
12 Months or Longer, Accumulated Loss	(9,398)	(10,848)
Fair value	191,350	243,859
Accumulated Loss	$ (10,520)	$ (13,668)

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.

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479081/326-30-55-8

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-7

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-5

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-5

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479081/326-30-55-8

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-6

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

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

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=plmr_SpecialRevenueExcludingAssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=plmr_CorporateDebtSecuritiesAndOtherDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: