Investments - Credit quality indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Investments
Held to maturity securities, net	$ 133,665	$ 150,941
Aaa
Investments
Held to maturity securities, net	44,971	59,901
Aa1/Aa2/Aa3
Investments
Held to maturity securities, net	38,183	38,496
A1/A2
Investments
Held to maturity securities, net	3,171	3,195
Baa1/Baa2
Investments
Held to maturity securities, net	1,000	1,003
Not rated
Investments
Held to maturity securities, net	$ 46,340	$ 48,346

Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

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