Hamilton Insurance (HG) 10-Q 6 Dec 23 2023 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2023	Dec. 05, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-41862
Entity Registrant Name	Hamilton Insurance Group, Ltd.
Entity Incorporation, State or Country Code	D0
Entity Tax Identification Number	98-1153847
Entity Address, Address Line One	Wellesley House North, 1st Floor
Entity Address, Address Line Two	90 Pitts Bay Road
Entity Address, City or Town	Pembroke
Entity Address, Postal Zip Code	HM 08
Entity Address, Country	BM
City Area Code	441
Local Phone Number	405-5200
Title of 12(b) Security	Class B common shares, par value $0.01 per share
Trading Symbol	HG
Security Exchange Name	NYSE
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		56,036,067
Entity Central Index Key	0001593275
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3

Unaudited Condensed Consolidate

Unaudited Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets
Investments, at fair value	$ 1,980,439	$ 1,545,587
Investments in Two Sigma Funds, at fair value (cost 2023: $891,791; 2022: $731,100)	979,986	740,736
Total investments	2,960,425	2,286,323
Cash and cash equivalents	804,548	1,076,420
Restricted cash and cash equivalents	98,979	130,783
Premiums receivable	689,042	522,670
Paid losses recoverable	138,314	90,655
Deferred acquisition costs	151,314	115,147
Unpaid losses and loss adjustment expenses recoverable	1,157,123	1,177,863
Receivables for investments sold	19,044	371
Prepaid reinsurance	232,211	164,313
Goodwill and intangible assets	89,589	86,958
Other assets	164,015	167,462
Total assets	6,504,604	5,818,965
Liabilities, non-controlling interest, and shareholders’ equity
Reserve for losses and loss adjustment expenses	2,948,822	2,856,275
Unearned premiums	951,596	718,188
Reinsurance balances payable	367,954	244,320
Payables for investments purchased	117,836	48,095
Term loan, net of issuance costs	149,801	149,715
Accounts payable and accrued expenses	159,681	138,050
Payables to related parties	9,060	20
Total liabilities	4,704,750	4,154,663
Non-controlling interest – TS Hamilton Fund	129	119
Shareholders’ equity
Common shares:	1,037	1,030
Additional paid-in capital	1,128,553	1,120,242
Accumulated other comprehensive loss	(4,441)	(4,441)
Retained earnings	674,576	547,352
Total shareholders’ equity	1,799,725	1,664,183
Total liabilities, non-controlling interest, and shareholders’ equity	6,504,604	5,818,965
Total fixed maturities
Assets
Investments, at fair value	1,631,471	1,259,476
Short-term investments
Assets
Investments, at fair value	348,968	286,111
Common Class A
Shareholders’ equity
Common shares:	305	305
Common Class B
Shareholders’ equity
Common shares:	427	420
Common Class C
Shareholders’ equity
Common shares:	$ 305	$ 305

Unaudited Condensed Consolida_2

Unaudited Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Investments, amortized cost	$ 2,077,885		$ 1,633,814
Investments in Two Sigma Funds, cost	$ 891,791		$ 731,100
Common stock, par value (in dollars per share)	$ 0.01
Common stock authorized (in shares)	150,000,000	135,000,000	135,000,000	135,000,000	135,000,000	135,000,000
Common stock issued (in shares)	103,704,006	103,683,894	103,087,859	103,087,859	103,039,304	102,563,042
Common stock outstanding (in shares)	103,704,006	103,683,894	103,087,859	103,087,859	103,039,304	102,563,042
Total fixed maturities
Investments, amortized cost	$ 1,730,262		$ 1,348,684
Short-term investments
Investments, amortized cost	$ 347,623		$ 285,130
Common Class A
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock authorized (in shares)	53,993,690	53,993,690	53,993,690	53,993,690	53,993,690	53,793,690
Common stock issued (in shares)	30,520,078	30,520,078	30,520,078	30,520,078	30,520,078	30,320,078
Common stock outstanding (in shares)	30,520,078	30,520,078	30,520,078	30,520,078	30,520,078	30,320,078
Common Class B
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock authorized (in shares)	65,480,684	50,480,684	50,480,684	50,480,684	48,984,123	46,898,612
Common stock issued (in shares)	42,658,302	42,638,190	42,042,155	42,042,155	40,497,039	37,935,266
Common stock outstanding (in shares)	42,658,302	42,638,190	42,042,155	42,042,155	40,497,039	37,935,266
Common Class C
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock authorized (in shares)	30,525,626	30,525,626	30,525,626	30,525,626	32,022,187	34,307,698
Common stock issued (in shares)	30,525,626	30,525,626	30,525,626	30,525,626	32,022,187	34,307,698
Common stock outstanding (in shares)	30,525,626	30,525,626	30,525,626	30,525,626	32,022,187	34,307,698

Unaudited Condensed Consolida_3

Unaudited Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues
Gross premiums written	$ 474,123	$ 400,811	$ 1,517,247	$ 1,305,421
Reinsurance premiums ceded	(90,557)	(100,000)	(400,475)	(366,933)
Net premiums written	383,566	300,811	1,116,772	938,488
Net change in unearned premiums	(46,530)	(5,868)	(164,374)	(107,021)
Net premiums earned	337,036	294,943	952,398	831,467
Net realized and unrealized gains (losses) on investments	47,343	(67,380)	101,881	146,640
Net investment income (loss)	8,069	(5,255)	17,719	(22,185)
Total realized and unrealized gains (losses) on investments and net investment income (loss)	55,412	(72,635)	119,600	124,455
Other income (loss)	2,386	2,727	7,838	9,117
Net foreign exchange gains (losses)	1,432	1,906	(3,953)	15,382
Total revenues	396,266	226,941	1,075,883	980,421
Expenses
Losses and loss adjustment expenses	191,577	257,963	519,554	597,014
Acquisition costs	78,537	65,735	220,532	194,795
General and administrative expenses	63,035	46,344	158,075	135,290
Amortization of intangible assets	2,794	3,178	7,869	9,874
Interest expense	5,288	4,102	16,007	11,255
Total expenses	341,231	377,322	922,037	948,228
Income (loss) before income tax	55,035	(150,381)	153,846	32,193
Income tax expense	2,387	1,054	6,908	3,103
Net income (loss)	52,648	(151,435)	146,938	29,090
Net income (loss) attributable to non-controlling interest	9,065	(15,318)	15,076	68,069
Net income (loss) and other comprehensive income (loss) attributable to common shareholders	$ 43,583	$ (136,117)	$ 131,862	$ (38,979)
Per share data
Basic income (loss) per share attributable to common shareholders (in dollars per share)	$ 0.42	$ (1.32)	$ 1.27	$ (0.38)
Diluted income (loss) per share attributable to common shareholders (in dollars per share)	$ 0.41	$ (1.32)	$ 1.26	$ (0.38)

Unaudited Condensed Consolida_4

Unaudited Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common shares	Additional paid-in capital	Accumulated other comprehensive income (loss)	Retained earnings
Balance, beginning of period at Dec. 31, 2021		$ 1,025	$ 1,110,248	$ (4,441)	$ 645,769
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares		7	308
Repurchases of common shares		(2)	(1,098)		(419)
Share compensation expense			9,817		0
Net income (loss)	$ 29,090				29,090
Net income attributable to non-controlling interest	(68,069)				(68,069)
Balance, end of period at Sep. 30, 2022	1,722,235	1,030	1,119,275	(4,441)	606,371
Balance, beginning of period at Jun. 30, 2022		1,030	1,115,077	(4,441)	742,488
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares		1	315
Repurchases of common shares		(1)	0		0
Share compensation expense			3,883		0
Net income (loss)	(151,435)				(151,435)
Net income attributable to non-controlling interest	15,318				15,318
Balance, end of period at Sep. 30, 2022	1,722,235	1,030	1,119,275	(4,441)	606,371
Balance, beginning of period at Dec. 31, 2022	1,664,183	1,031	1,120,242	(4,441)	547,352
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares		8	(8)
Repurchases of common shares		(2)	(1,776)		(469)
Share compensation expense			10,095		(4,169)
Net income (loss)	146,938				146,938
Net income attributable to non-controlling interest	(15,076)				(15,076)
Balance, end of period at Sep. 30, 2023	1,799,725	1,037	1,128,553	(4,441)	674,576
Balance, beginning of period at Jun. 30, 2023		1,036	1,124,566	(4,441)	630,993
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares		1	(1)
Repurchases of common shares		0	0		0
Share compensation expense			3,988		0
Net income (loss)	52,648				52,648
Net income attributable to non-controlling interest	(9,065)				(9,065)
Balance, end of period at Sep. 30, 2023	$ 1,799,725	$ 1,037	$ 1,128,553	$ (4,441)	$ 674,576

Unaudited Condensed Consolida_5

Unaudited Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Operating activities
Net income (loss)	$ 146,938	$ 29,090
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	8,990	11,699
Share compensation expense	10,095	9,817
Net realized (gains) losses on investments	(32,363)	(267,140)
Change in net unrealized (gains) losses on investments	(69,518)	120,500
Other items	1,330	18,473
Change in:
Premiums receivable	(166,372)	(131,081)
Paid losses recoverable	(47,659)	(22,804)
Deferred acquisition costs	(36,167)	(20,600)
Prepaid reinsurance	(67,898)	(41,917)
Unpaid losses and loss adjustment expenses recoverable	20,740	(38,586)
Other assets	3,253	4,167
Reserve for losses and loss adjustment expenses	92,547	340,706
Unearned premiums	233,408	154,052
Reinsurance balances payable	123,634	52,692
Accounts payable and accrued expenses and other	26,711	(30,032)
Net cash provided by (used in) operating activities	247,669	189,036
Investing activities
Proceeds from redemptions from Two Sigma Funds	1,821,046	2,126,103
Contributions to Two Sigma Funds	(1,954,119)	(1,846,409)
Purchases of fixed maturity investments	(809,646)	(608,310)
Proceeds from sales, redemptions and maturity of fixed maturity investments	418,677	402,078
Purchases of short-term investments	(1,078,631)	(1,319,143)
Proceeds from sales of short-term investments	1,032,091	1,573,700
Change in receivables for investments sold	(18,673)	(8,483)
Change in payables for investments purchased	69,741	(21,145)
Other	(11,425)	(7,541)
Net cash provided by (used in) investing activities	(530,939)	290,850
Financing activities
Issuance of common shares	8	7
Repurchases of common shares and options	(2,247)	(1,519)
Contribution of additional paid-in capital	(8)	308
Term loan renewal costs	0	(345)
Withdrawal of non-controlling interest	(15,066)	(68,049)
Net cash provided by (used in) financing activities	(17,313)	(69,598)
Effect of exchange rate changes on cash and cash equivalents and restricted cash and cash equivalents	(3,093)	(22,158)
Net increase (decrease) in cash and cash equivalents and restricted cash and cash equivalents	(303,676)	388,130
Cash and cash equivalents and restricted cash and cash equivalents, beginning of period	1,207,203	964,126
Cash and cash equivalents and restricted cash and cash equivalents, end of period	$ 903,527	$ 1,352,256

Organization

Organization	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Hamilton Insurance Group, Ltd. ("Hamilton Group", the "Group" or the "Company"), the ultimate group holding company, was incorporated on September 4, 2013, under the laws of Bermuda. Our Bermuda operations are led by Hamilton Re, Ltd. ("Hamilton Re"), a registered Class 4 insurer incorporated in Bermuda. Hamilton Re writes property, casualty, and specialty insurance and reinsurance on a global basis. Hamilton Re US is a tax partnership that was formed pursuant to an arrangement between Hamilton Re and its Bermuda-incorporated affiliate, Hamilton ILS Holdings Limited. The tax partnership is treated as a U.S. corporation for U.S. tax purposes and is registered with the U.S. Internal Revenue Service, such that capital and profits allocated to Hamilton Re US are subject to applicable U.S. taxation. Ada Capital Management Limited (“ACML”), a wholly owned insurance agent incorporated and regulated in Bermuda, is authorized to underwrite on behalf of Ada Re, Ltd. (“Ada Re”). Our London operations are comprised of Hamilton Managing Agency Limited (“HMA”), a Lloyd’s managing agency, which manages our wholly aligned Syndicate 4000 and certain other third-party funded Lloyd’s Syndicates. Syndicate 4000 operates in the Lloyd’s market and underwrites property, casualty, and specialty insurance and reinsurance business on a subscription basis. Syndicate 3334, which was managed by HMA, was closed by way of a Reinsurance to Close (“RITC”) into Syndicate 4000 at December 31, 2021. Our Dublin operations are comprised of Hamilton Insurance Designated Activity Company ("HIDAC"), a Dublin-based insurer with a U.K. branch and extensive licensing in the United States, including excess and surplus lines and reinsurance in all 50 states. Hamilton Managing General Agency Americas LLC ("HMGA Americas") is licensed throughout the United States and underwrites on behalf of the Group's London, Dublin and Bermuda operations solely in respect of Hamilton Re US, providing access from the U.S. to the Lloyd's market, the Group's rated Irish carrier and the Group's Bermuda balance sheet, respectively. Hamilton Select Insurance Inc. ("Hamilton Select") is a U.S. domestic excess and surplus lines carrier incorporated in Delaware and authorized to write excess and surplus business in all 50 states. Two Sigma Hamilton Fund, LLC ("TS Hamilton Fund"), is a Delaware limited liability company. In 2013, Hamilton Re entered into a limited liability company agreement with TS Hamilton Fund and Two Sigma Principals, LLC (the "Managing Member") as the managing member of TS Hamilton Fund. Effective July 1, 2023, Hamilton Re has committed to an investment in TS Hamilton Fund in an amount up to the lesser of (i) $1.8 billion or (ii) 60% of Hamilton Group’s net tangible assets (previously equal to a minimum of 95% of the consolidated net tangible assets of Hamilton Group). TS Hamilton Fund has engaged Two Sigma Investments, LP ("Two Sigma"), a related party Delaware limited partnership, to serve as its investment manager. Two Sigma is a United States Securities and Exchange Commission registered investment adviser specializing in quantitative analysis (see Note 3, Investments for further details). Unconsolidated Related Parties Ada Re is a special purpose insurer funded by third party investors and formed to provide fully collateralized reinsurance and retrocession to both Hamilton Group and third-party cedants. Turing Re Ltd. ("Turing Re"), a Bermuda special purpose insurer funded by investors, provides collateralized reinsurance capacity for Hamilton Re’s property treaty business. Easton Re is an industry loss index-triggered catastrophe bond that provides the Company's operating platforms with multi-year risk transfer capacity of $150 million to protect against named storm and earthquake risk in the United States.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2022, as included in the Group’s most recently filed IPO prospectus (the "Prospectus") dated November 9, 2023, filed with the Securities and Exchange Commission on November 13, 2023. There have been no material changes to the Company's significant accounting policies as described in the Company's audited consolidated financial statements for the year ended December 31, 2022, as included in the Prospectus. a. Basis of Presentation These unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP") and Article 10 of Regulation S-X, for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In addition, the year-end balance sheet data was derived from audited financial statements but does not include all disclosures required by GAAP. In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the Company's financial position and results of operations as at the end of, and for, the periods presented. These financial statements include the accounts of Hamilton Group, Hamilton Re, Hamilton U.K. Holdings Limited, Hamilton Select, HMGA Americas, ACML, and TS Hamilton Fund (collectively the "Company"). All significant intercompany transactions and balances have been eliminated on consolidation . Certain comparative information has been reclassified to conform to the current year presentation. b. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported and disclosed amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The major estimates recorded in the Company’s financial statements include, but are not limited to, premiums written, provisions for estimated future credit losses, the reserve for losses and loss adjustment expenses and the fair value of investments. c. Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02 Leases (as subsequently clarified in various Updates) which updated accounting guidance that applies to any entity that enters into a lease that does not meet certain scope exceptions. The guidance requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous guidance. The Company adopted this guidance in the first quarter of 2022 by recording a gross-up of the balance sheet in recognition of an operating lease liability for future lease payments and the associated right-of-use asset for the right to use the underlying asset over the lease term. This guidance did not have a material impact on the Company’s results of operations, financial position, cash flows or disclosures. In June 2016, the FASB issued ASU 2016-13 Measurement of Credit Losses on Financial Instruments

Investments

Investments	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Fixed Maturity and Short-Term Investments - Trading The Company’s fixed maturity and short-term investments at September 30, 2023 and December 31, 2022 are as follows: 2023 (Expressed in thousands of U.S. Dollars) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities: U.S. government treasuries $ 651,446 $ 21 $ (32,381) $ 619,086 U.S. states, territories and municipalities 4,729 — (375) 4,354 Non-U.S. sovereign governments and supranationals 44,759 413 (1,840) 43,332 Corporate 853,433 81 (42,177) 811,337 Residential mortgage-backed securities - Agency 148,097 — (20,117) 127,980 Residential mortgage-backed securities - Non-agency 4,763 2 (821) 3,944 Commercial mortgage-backed securities - Non-agency 10,188 — (1,295) 8,893 Other asset-backed securities 12,847 15 (317) 12,545 Total fixed maturities 1,730,262 532 (99,323) 1,631,471 Short-term investments 347,623 1,345 — 348,968 Total $ 2,077,885 $ 1,877 $ (99,323) $ 1,980,439 2022 (Expressed in thousands of U.S. Dollars) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities: U.S. government treasuries $ 498,841 $ 99 $ (27,089) $ 471,851 U.S. states, territories and municipalities 4,741 — (434) 4,307 Non-U.S. sovereign governments and supranationals 14,191 363 (1,602) 12,952 Corporate 690,900 363 (43,786) 647,477 Residential mortgage-backed securities - Agency 111,234 — (14,824) 96,410 Residential mortgage-backed securities - Non-agency 5,147 — (772) 4,375 Commercial mortgage-backed securities - Non-agency 10,283 — (1,064) 9,219 Other asset-backed securities 13,347 1 (463) 12,885 Total fixed maturities 1,348,684 826 (90,034) 1,259,476 Short-term investments 285,130 986 (5) 286,111 Total $ 1,633,814 $ 1,812 $ (90,039) $ 1,545,587 Contractual Maturities Summary The following table presents contractual maturities of fixed maturity securities at September 30, 2023. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. 2023 (Expressed in thousands of U.S. Dollars) Amortized Cost Fair Value Due less than one year $ 139,886 $ 135,950 Due after one through five years 1,164,512 1,107,734 Due after five through ten years 245,255 230,867 Due after ten years 4,714 3,558 Mortgage-backed 163,048 140,817 Asset-backed 12,847 12,545 Total $ 1,730,262 $ 1,631,471 Investments in Two Sigma Funds The Company’s investments in Two Sigma Funds at September 30, 2023 and December 31, 2022 are as follows: 2023 2022 (Expressed in thousands of U.S. Dollars) Cost Net Unrealized Gains (Losses) Fair Value Cost Net Unrealized Gains (Losses) Fair Value Two Sigma Futures Portfolio, LLC (FTV) $ 469,379 $ (7,212) $ 462,167 $ 438,625 $ (95,213) $ 343,412 Two Sigma Spectrum Portfolio, LLC (STV) 239,819 54,115 293,934 171,135 57,982 229,117 Two Sigma Equity Spectrum Portfolio, LLC (ESTV) 182,593 41,292 223,885 121,340 46,867 168,207 Total $ 891,791 $ 88,195 $ 979,986 $ 731,100 $ 9,636 $ 740,736 The Company, through its investments in FTV, STV and ESTV, seeks to achieve absolute dollar-denominated returns on a substantial capital base, primarily by combining multiple hedged and leveraged systematic investment strategies with proprietary risk management and execution techniques. These systematic strategies include, but are not limited to, technical and statistically-based, fundamental-based, event-based, market condition-based and spread-based strategies as well as contributor-based and/or sentiment-based strategies and blended strategies. FTV primarily utilizes systematic strategies to gain broad macro exposure to FX, fixed income, equity and credit indices, and commodities, predominantly by trading futures, spots, forwards, options, swaps, cash bonds and exchange traded products. STV primarily utilizes systematic strategies to trade U.S.-listed equity securities and related instruments and derivatives. ESTV primarily utilizes systematic strategies to trade non-U.S.-listed equity securities and related instruments and derivatives. At September 30, 2023, the Company owns a 20.1%, 16.1% and 8.6% interest in each of the FTV, STV and ESTV funds, respectively. The following table summarizes certain investments of FTV, STV and ESTV where TS Hamilton Fund’s proportionate share of the fair value of the investment represents more than 5% of TS Hamilton Fund’s members’ equity at September 30, 2023: 2023 (Expressed in thousands of U.S. Dollars) Principal / Shares (1) Fair Value (1) % of Members' Equity State Street Treasury Obligations Money Market Fund 126,802 $ 126,802 7.5 % U.S. Treasury Securities, 0.0000% - 4.6250%, due 10/5/2023 - 8/15/2043 710,830 $ 704,227 41.5 % U.K. Gilt Securities, 1.6250%, due 10/22/2028 604 $ 650 — % U.K. Gilt Securities, 3.2500% - 3.7500%, due 1/31/2033 - 10/22/2053 (82,909) $ (89,773) (5.3) % U.S. Treasury Securities, 3.8750% - 5.0000%, due 9/30/2025 - 8/15/2023 (240,013) $ (236,195) (13.9) % (1) Values represent TS Hamilton Fund’s proportionate share of the aggregate of FTV, STV and ESTV total holdings. Two Sigma and the Managing Member are related parties to the Company as described further in Note 1, Organization . Effective July 1, 2023, a revised investment management agreement with Two Sigma requires TS Hamilton Fund to incur a management fee of 2.5% of the non-managing members' equity in the net asset value of the TS Hamilton Fund per annum (previously 3%). The management fee for the three months ended September 30, 2023 and 2022 was $10.4 million and $14.0 million, respectively, and the management fee for the nine months ended September 30, 2023 and 2022 was $34.4 million and $39.5 million, respectively. Under the terms of the revised limited liability company agreement between Hamilton Re and the Managing Member, the Managing Member remains entitled to an incentive allocation equal to 30% of TS Hamilton Fund’s net profits, subject to high watermark provisions, and adjusted for withdrawals and any incentive allocation to the Managing Member. In the event there is a net loss during a quarter and a net profit during any subsequent quarter, the Managing Member is entitled to a modified incentive allocation whereby the regular incentive allocation will be reduced by 50% until subsequent cumulative net profits are credited in an amount equal to 200% of the previously allocated net losses. The Managing Member is also entitled to receive a revised additional incentive allocation as of the end of each fiscal year (or on any date Hamilton Re withdraws all or a portion of its capital), in an amount equal to 25% of the Excess Profits (previously 20%). “Excess Profits” for any given fiscal year (or other such accounting period) means the net profits over 10% for such fiscal year (previously 15%), net of management fees and expenses and gross of incentive allocations, but only after recouping previously unrecouped net losses. To the extent Hamilton Re contributes capital other than at the beginning of a fiscal year or withdraws capital other than at the end of a fiscal year, the additional incentive allocation hurdle with respect to such capital is prorated. The aggregate incentive allocation (inclusive of the additional incentive allocation) for the three months ended September 30, 2023 and 2022 was $9.1 million and $(15.3) million, respectively, and the aggregate incentive allocation (inclusive of the additional incentive allocation) for the nine months ended September 30, 2023 and 2022 was $15.1 million and $68.0 million, respectively. Hamilton Re has a commitment with TS Hamilton Fund to maintain an amount up to the lesser of (i) $1.8 billion or (ii) 60% of Hamilton Insurance Group’s net tangible assets in TS Hamilton Fund, such lesser amount, the “Minimum Commitment Amount”, for a three-year period (the "Initial Term") and for rolling three-year periods thereafter (each such three-year period the "Commitment Period"), subject to certain circumstances and the liquidity options described below, with the Commitment Period ending on December 31, 2025. The Commitment Period consists of a 3-year rolling term that automatically renews on an annual basis unless Hamilton Re or the Managing Member provide advance notice of non-renewal. The TS Hamilton Fund generally has two liquidity options, subject to Hamilton Re’s minimum investment commitment, which are as follows: • Monthly liquidity - Subject to certain conditions, Hamilton Re may request a whole or partial withdrawal of its capital account, no later than fifteen days prior to the end of a calendar month, effective as of the last day of such calendar month. • Daily liquidity - Subject to certain limited circumstances, including the need to meet obligations pursuant to Hamilton Re’s underwriting operations, Hamilton Re may request a withdrawal of all or a portion of its capital account upon at least one At its discretion, the Managing Member may permit or require Hamilton Re to withdraw all or any portion of its respective capital account at other times, or waive or reduce certain notice periods, or allow a notice to be revoked. The Managing Member may withdraw all or any portion of its capital account at any time. Total Realized and Unrealized Gains (Losses) on Investments and Net Investment Income (Loss) The components of total realized and unrealized gains (losses) on investments and net investment income (loss) for the three and nine months ended September 30, 2023 and 2022 are as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Net realized and unrealized gains (losses) on investments: Net realized gains (losses) on investments $ 42,403 $ 115,129 $ 32,363 $ 267,140 Change in net unrealized gains (losses) on investments 4,940 (182,509) 69,518 (120,500) Net realized and unrealized gains (losses) on investments 47,343 (67,380) 101,881 146,640 Net investment income (loss): Fixed maturities 12,208 5,880 31,178 14,343 Short-term investments 38 334 287 737 TS Hamilton Fund 3,121 3,095 13,033 4,603 Cash and cash equivalents 4,029 544 8,752 696 Other (104) (431) 1,015 (1,230) Interest and other 19,292 9,422 54,265 19,149 Management fees (10,958) (14,420) (35,806) (40,601) Other expenses (265) (257) (740) (733) Net investment income (loss) 8,069 (5,255) 17,719 (22,185) Total realized and unrealized gains (losses) on investments and net investment income (loss) $ 55,412 $ (72,635) $ 119,600 $ 124,455 ` Net Realized Gains (Losses) on Investments The components of net realized gains (losses) on investments for the three and nine months ended September 30, 2023 and 2022 are as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Fixed maturities and short-term investments $ (7,688) $ (3,313) $ (10,796) $ (13,684) TS Hamilton Fund 50,091 118,442 42,948 279,977 Other — — 211 847 Net realized gains (losses) on investments $ 42,403 $ 115,129 $ 32,363 $ 267,140 Net Unrealized Gains (Losses) on Investments The components of net unrealized gains (losses) on investments for the three and nine months ended September 30, 2023 and 2022 are as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Fixed maturities and short-term investments $ (12,818) $ (38,556) $ (9,800) $ (101,760) TS Hamilton Fund 17,758 (143,953) 79,318 (18,740) Net realized gains (losses) on investments $ 4,940 $ (182,509) $ 69,518 $ (120,500) Pledged Assets At September 30, 2023 and December 31, 2022, pledged investments at fair value were comprised of $226.9 million and $274.0 million, respectively, securing a portion of the capital requirements for business written at Lloyd's, $54.1 million and $39.0 million, respectively, held in trust accounts for the benefit of U.S. state regulatory authorities and $34.9 million and $Nil, respectively, securing other underwriting obligations. In addition, certain investments were pledged as security for letter of credit facilities as described further in Note 10, Debt and Credit Facilities . At September 30, 2023 and December 31, 2022, restricted cash and cash equivalents balances were comprised of $95.5 million and $126.8 million, respectively, securing other underwriting obligations, $1.8 million and $2.1 million, respectively, securing a portion of the capital requirements for business written at Lloyd's, $1.4 million and $1.3 million, respectively, in trust accounts for the benefit of regulatory authorities, and $0.3 million and $0.6 million, respectively, of escrow funds. Total cash and cash equivalents and restricted cash and cash equivalents of $903.5 million presented in the statement of cash flows at September 30, 2023 was comprised of cash and cash equivalents of $804.5 million and restricted cash and cash equivalents of $99.0 million on the balance sheet. Total cash and cash equivalents and restricted cash and cash equivalents of $1.2 billion presented in the statement of cash flows at December 31, 2022 was comprised of cash and cash equivalents of $1.1 billion and restricted cash and cash equivalents of $130.8 million on the balance sheet.

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Financial Instruments Subject to Fair Value Measurements Accounting guidance over fair value measurements requires that a fair value measurement reflect the assumptions market participants would use in pricing an asset or liability based on the best information available. Assumptions include the risks inherent in a particular valuation technique (such as a pricing model) and/or the risks inherent in the inputs to the model. The fair value of a financial instrument is the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (the “exit price”). Instruments that the Company owns are marked to bid prices. Basis of Fair Value Measurements Fair value measurement accounting guidance also establishes a fair value hierarchy that prioritizes the inputs to the respective valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). An asset or liability’s classification within the fair value hierarchy is based on the lowest level of significant input to its valuation. The three levels of the fair value hierarchy are: • Level 1 - Inputs that reflect unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date; • Level 2 - Inputs other than quoted prices included within Level 1 that are observable for the asset or liability either directly or indirectly, including inputs in markets that are not considered to be active; and • Level 3 - Inputs that are both significant to the fair value measurement and unobservable. Assets Recorded at Fair Value - Fixed Maturity and Short-term Investments The following section describes the valuation methodologies used to determine the fair value of the Company’s fixed maturity and short-term investments by asset class: • U.S. government treasuries: fair value based on observable market inputs such as quoted prices, reported trades, quoted prices for similar issuances and benchmark yields; • U.S. states, territories and municipalities: fair value based on observable market inputs such as quoted market prices, quoted prices for similar securities, benchmark yields and credit spreads; • Non-U.S. sovereign governments and supranationals: fair value based on observable market inputs such as quoted market prices, quoted prices for similar securities and models with observable inputs such as benchmark yields and credit spreads, and then, where applicable, converted to U.S. dollars using an exchange rate from a nationally recognized source; • Corporate: fair value based on observable market inputs such as quoted market prices, quoted prices for similar securities, benchmark yields and credit spreads; • Asset-backed and mortgage-backed securities: fair value based on observable inputs such as quoted prices, reported trades, quoted prices for similar issuances or benchmark yields and cash flow models using observable inputs such as prepayment speeds, collateral performance and default spreads; and • Short-term investments: fair value based on observable market inputs such as quoted prices, reported trades, quoted prices for similar issuances and benchmark yields. The following table presents the financial instruments measured at fair value on a recurring basis at September 30, 2023 and December 31, 2022: 2023 (Expressed in thousands of U.S. Dollars) Level 1 Level 2 Level 3 Total Fixed maturities: U.S. government treasuries $ — $ 619,086 $ — $ 619,086 U.S. states, territories and municipalities — 4,354 — 4,354 Non-U.S. sovereign governments and supranationals — 43,332 — 43,332 Corporate — 811,337 — 811,337 Residential mortgage-backed securities - Agency — 127,980 — 127,980 Residential mortgage-backed securities - Non-agency — 3,944 — 3,944 Commercial mortgage-backed securities - Non-agency — 8,893 — 8,893 Other asset-backed securities — 12,545 — 12,545 Total fixed maturities — 1,631,471 — 1,631,471 Short-term investments — 348,968 — 348,968 Total $ — $ 1,980,439 $ — $ 1,980,439 2022 (Expressed in thousands of U.S. Dollars) Level 1 Level 2 Level 3 Total Fixed maturities: U.S. government treasuries $ — $ 471,851 $ — $ 471,851 U.S. states, territories and municipalities — 4,307 — 4,307 Non-U.S. sovereign governments and supranationals — 12,952 — 12,952 Corporate — 647,477 — 647,477 Residential mortgage-backed securities - Agency — 96,410 — 96,410 Residential mortgage-backed securities - Non-agency — 4,375 — 4,375 Commercial mortgage-backed securities - Non-agency — 9,219 — 9,219 Other asset-backed securities — 12,885 — 12,885 Total fixed maturities — 1,259,476 — 1,259,476 Short-term investments — 286,111 — 286,111 Total $ — $ 1,545,587 $ — $ 1,545,587

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities TS Hamilton Fund TS Hamilton Fund meets the definition of a variable interest entity ("VIE") principally because the Managing Member does not hold substantive equity at risk in the entity but controls all of the decision making authority over it. Therefore, the Company assessed its ownership in the VIE to determine if it is the primary beneficiary. The Managing Member is a related party to the Company and collectively they hold all of the variable interest. The Company performed an assessment of all relevant facts and circumstances and determined that it is the entity within the related party group for whom substantially all of the activities of the VIE are conducted. As a result, the Company concluded that it is the primary beneficiary of TS Hamilton Fund. Activity in the non-controlling interest of TS Hamilton Fund for the three and nine months ended September 30, 2023 and 2022 was as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Balance - beginning of period $ 124 $ 15,462 $ 119 $ 124 Withdrawals (9,060) — (15,066) (68,049) Equity in earnings 5 (1) 10 20 Incentive allocation 9,060 (15,317) 15,066 68,049 Balance - end of period $ 129 $ 144 $ 129 $ 144 The following table represents the total assets and total liabilities of TS Hamilton Fund at September 30, 2023 and December 31, 2022. Creditors or beneficial interest holders of TS Hamilton Fund have no recourse to the general credit of the Company as the Company’s obligation is limited to the amount of its committed investment. (Expressed in thousands of U.S. Dollars) 2023 2022 Assets Cash and cash equivalents $ 450,759 $ 800,239 Short-term investments 347,787 264,104 Investments in Two Sigma Funds, at fair value 979,986 740,736 Receivables for investments sold 12,730 — Interest and dividends receivable 804 2,076 Total assets 1,792,066 1,807,155 Liabilities Accounts payable and accrued expenses 254 291 Withdrawal payable 9,060 145,738 Payable for investments purchased 86,933 48,095 Total liabilities 96,247 194,124 Total net assets managed by TS Hamilton Fund $ 1,695,819 $ 1,613,031 The withdrawal payable of $9.1 million and $145.7 million at September 30, 2023 and December 31, 2022, respectively, includes a redemption of $Nil and $145.7 million, respectively, due to Hamilton Re. The net balance is reported on the Company's balance sheet in "Payables to related parties".

Value Appreciation Pool

Value Appreciation Pool	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Value Appreciation Pool	Value Appreciation Pool The Value Appreciation Pool ("VAP") represents an accrual in respect of the Company's estimated liability under a long-term incentive compensation plan that rewards employees with 10% of any increase in the multiple of the Company's estimated fair market value to GAAP shareholders' equity between the December 1, 2020 VAP inception date, and either an interim Trigger Event or the ultimate plan maturity on December 31, 2025. A total of 10.0 million units are available for issuance under this plan. As of September 30, 2023, there were 9.5 million units issued and outstanding. With effect from March 10, 2023, the VAP was revised to include an Underpin, such that if the ratio of the Company's estimated fair market value to GAAP shareholders' equity on the Trigger Event date is less than 1.15, the value of the award will be calculated with reference to a minimum ratio of 1.15 in order to provide for a minimum payment in respect of the award. In the event that the Underpin comes into effect, the fair value of the VAP at the offering date is estimated to be approximately $5.00 per VAP unit. The award vests in two tranches, subject to continued service: either 50% upon the ultimate plan maturity date of November 30, 2025 and 50% twelve months later, or 50% on each of the first and second anniversaries of a Trigger Event if one occurs prior to the maturity date. Participants who leave prior to vesting forfeit any previously unsettled portion of their awards. The award may be settled in either cash or shares, solely at the discretion of the Company. As a private company, the VAP was initially measured at intrinsic value and no compensation cost was recorded over the period December 1, 2020 to March 31, 2023. On May 15, 2023, the Company became a public business entity and the VAP was remeasured at fair value. The fair value of the compensation cost is estimated at each reporting date and expensed over the period for which the employee is required to provide services in exchange for the award, with any changes recorded in compensation expense by a cumulative catch-up adjustment. During the three and nine months ended September 30, 2023, the Company recorded compensation expense of $11.2 million and $15.6 million, respectively. $4.2 million of this expense was recorded as an adjustment to retained earnings in "Share compensation expense" in the second quarter of 2023. The aggregate fair value of the VAP was estimated on September 30, 2023 using the following assumptions: Inputs Actual Expected volatility 26.70% Risk-free rate 4.95% Expected life 2.28 years The volatility assumption is derived from the median of the volatility of a select group of peer companies. The risk-free interest rate is based on the conversion of semi-annual zero-coupon U.S. Treasury rates as of the Valuation Date to continuously compounded rates and a rate selection commensurate with the remaining projected period. The expected life of the award was estimated at the remaining time to VAP maturity, assuming no prior Trigger Event occurs. An equity valuation assumption is also used in the Monte Carlo simulation.

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2023
Insurance [Abstract]
Reinsurance	Reinsurance The Company purchases reinsurance and other protection to manage its risk portfolio and to reduce its exposure to large losses. The Company currently has in place contracts that provide for recovery of a portion of certain claims and claim expenses, generally in excess of various retentions or on a proportional basis. Amounts recoverable under reinsurance contracts are recorded as assets. The Company remains liable to the extent that any reinsurance company fails to meet its obligations. Allowance for Expected Credit Losses Premiums receivable and paid and unpaid losses recoverable comprise the Company's most significant credit exposures not carried at fair value. The Company has not historically experienced significant credit losses. In determining an allowance for these assets, the Company considers historical information in combination with counterparty financial strength ratings and the extent to which balances are collateralized. The Company assesses the risk of future default by evaluating current market conditions for the likelihood of default and calculates its provision for current expected credit losses under the probability of default and loss given default methodology. Premiums Receivable Premiums receivable are estimated based on policy terms and reports received from the underlying counterparties, supplemented by management's judgment. Due to the nature of the (re)insurance business, the Company routinely receives reports and premiums subsequent to the inception of the coverage period. At September 30, 2023, the Company’s premiums receivable balance, net of credit provisions of $2.7 million, was $689.0 million. At December 31, 2022, the Company’s premiums receivable balance, net of credit provisions of $2.9 million, was $522.7 million. Reinsurance Balances Recoverable Reinsurance balances recoverable is comprised of amounts due from reinsurers based on the claim liabilities associated with the reinsured policy. The Company accrues amounts due from reinsurers based on estimated ultimate contract losses. At September 30, 2023, the Company’s paid and unpaid reinsurance recoverable balances net of credit provisions were $138.3 million and $1.2 billion, respectively, with a total corresponding provision for current expected credit losses of $0.7 million. At December 31, 2022, the Company’s paid and unpaid reinsurance recoverable balances net of credit provisions were $90.7 million and $1.2 billion, respectively, with a total corresponding provision for current expected credit losses of $0.8 million. At September 30, 2023 and December 31, 2022, the distribution of the Company’s paid losses recoverable and unpaid losses and loss adjustment expenses recoverable as categorized by major rating agencies were as follows: % of total paid and unpaid losses and loss adjustment expenses recoverable Classification September 30, December 31, Collateralized 28.7 % 33.8 % A- or better 70.6 % 65.6 % Below A- 0.7 % 0.6 % Total 100.0 % 100.0 % At September 30, 2023 and December 31, 2022, the three largest balances by reinsurer accounted for 27%, 19% and 12%, and 31%, 17% and 11%, respectively, of paid losses recoverable and unpaid losses and loss adjustment expenses recoverable. Loss Portfolio Transfer On February 6, 2020, the Company entered into a loss portfolio transfer agreement (the "LPT"), under which the insurance liabilities arising from certain casualty risks for the Lloyd's Years of Account ("YOA") 2016, 2017 and 2018 were retroceded to a third party in exchange for total premium of $72.1 million. This transaction was accounted for as retroactive reinsurance under which cumulative ceded losses exceeding the LPT premium are recognized as a deferred gain liability and amortized into income over the settlement period of the ceded reserves in proportion to cumulative losses collected over the estimated ultimate reinsurance recoverable. The amount of the deferral is recalculated each reporting period based on updated ultimate loss estimates. Consequently, cumulative adverse development subsequent to the signing of the LPT may result in significant losses from operations until periods when the deferred gain is recognized as a benefit to earnings. At September 30, 2023 and December 31, 2022, the balance of reinsurance recoverable on unpaid losses due under this LPT was $50.7 million and $59.2 million, respectively. Amortization of the deferred gain was an expense of $0.9 million and income of $3.7 million during the three months ended September 30, 2023 and 2022, respectively, and income of $2.5 million and $1.7 million during the nine months ended September 30, 2023 and 2022, respectively, which was recorded through losses and loss adjustment expenses in accordance with the actual loss payments and updated estimates of ultimate losses of the subject business. Catastrophe Bond Reinsurance

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2023
Insurance [Abstract]
Reserve for Losses and Loss Adjustment Expenses	Reserve for Losses and Loss Adjustment Expenses The following table presents a reconciliation of unpaid losses and loss adjustment expenses ("LAE") for the nine months ended September 30, 2023 and 2022: (Expressed in thousands of U.S. Dollars) 2023 2022 Gross unpaid losses and loss expenses, beginning of period $ 2,856,275 $ 2,415,491 Reinsurance recoverable on unpaid losses 1,177,863 1,112,543 Net unpaid losses and loss expenses, beginning of period 1,678,412 1,302,948 Net losses and loss expenses incurred in respect of losses occurring in: Current year 528,457 600,536 Prior years (8,903) (3,522) Total incurred 519,554 597,014 Net losses and loss expenses paid in respect of losses occurring in: Current year 28,521 18,901 Prior years 397,407 236,661 Total paid 425,928 255,562 Foreign currency revaluation and other 19,661 (39,331) Net unpaid losses and loss expenses, end of period 1,791,699 1,605,069 Reinsurance recoverable on unpaid losses 1,157,123 1,151,128 Gross unpaid losses and loss expenses, end of period $ 2,948,822 $ 2,756,197 Net favorable prior year development of $8.9 million for the nine months ended September 30, 2023 was comprised of $4.9 million and $4.0 million of favorable prior year development on catastrophe and attritional losses, respectively. See below for further details: • Net favorable development of $20.3 million on specialty contracts, driven by lower than expected claims development across various classes; offset by • Net unfavorable development of $8.8 million on casualty contracts, primarily related to higher than expected claims development across various classes; and • Net unfavorable development of $6.6 million on property contracts, primarily driven by higher than expected claims related to Winterstorm Elliott and development on certain attritional claims, including claims arising from exited classes of business. In addition, casualty business protected by the LPT discussed in Note 7, Reinsurance, recorded favorable gross development, which, in addition to amortization of the associated deferred gain, resulted in a net positive earnings impact of $4.0 million. Net favorable prior year development of $3.5 million for the nine months ended September 30, 2022 was comprised of $15.0 million of favorable prior year development on catastrophe losses offset by $11.5 million of unfavorable prior year development on attritional losses. See below for further details: • Net favorable development of $23.6 million on specialty contracts, driven by reductions in loss estimates; and • Net favorable development of $1.6 million on property contracts, driven by reductions in loss estimates; offset by • Net unfavorable development of $27.7 million on casualty contracts, including claims arising from exited classes of business. . In addition, casualty business protected by the LPT discussed in Note 7, Reinsurance, recorded favorable gross development which was partially offset by amortization of the associated deferred gain, resulting in a net positive earnings impact of $6.0 million. Reinsurance recoverable on unpaid losses related to the LPT discussed in Note 7, Reinsurance was recognized for each of the nine months ended September 30, 2023 and 2022 in the reconciliation of beginning and ending gross and net loss and LAE reserves presented above. The Company amortized acquisition costs of $78.5 million and $65.7 million for the three months ended September 30, 2023 and 2022, respectively, and $220.5 million and $194.8 million for the nine months ended September 30, 2023 and 2022, respectively. Ukraine Conflict The estimate of net reserves for losses and loss adjustment expenses related to the ongoing Ukraine conflict is subject to significant uncertainty. As at September 30, 2023 and December 31, 2022, our recorded reserves relating to the Ukraine conflict totaled $66.2 million and $79.3 million, respectively. Covid-19 Our Covid-19 losses also remain subject to significant uncertainty. Actual ultimate losses for these events may differ materially from the Company's current estimates. As at September 30, 2023 and December 31, 2022, our recorded reserves relating to Covid-19 totaled $13.9 million and $39.0 million, respectively. While the Company believes, based on current facts and circumstances, that its estimates of net reserves for losses and loss adjustment expenses are adequate for losses and loss adjustment expenses that have been incurred at September 30, 2023, the Company will continue to monitor its assumptions as new information becomes available and will adjust its estimate of net reserves for losses and loss adjustment expenses as appropriate. Actual ultimate losses for these events may differ materially from the Company's current estimates.

Segment Reporting

Segment Reporting	9 Months Ended
	Sep. 30, 2023
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting We have determined our reportable business segments based on the information used by management in assessing performance and allocating resources to underwriting operations. We have identified two reportable business segments - International and Bermuda. Each of our identified reportable segments has a Chief Executive Officer who is responsible for the overall profitability of their segment and who regularly reports and is directly accountable to the chief operating decision maker: the Chief Executive Officer of the consolidated group. We evaluate reportable segment performance based on their respective underwriting income or loss. Underwriting income or loss is calculated as net premiums earned less losses and loss adjustment expenses, acquisition costs, and other underwriting expenses (net of third party fee income). General and administrative expenses not incurred by the reportable segments are included in corporate and other expenses as part of the reconciliation of net underwriting income or loss to net income or loss attributable to common shareholders. As we do not manage our assets by reportable segment, investment income and assets are not allocated to reportable segments. Our core business is underwriting and our underwriting results are reflected in our reportable segments: (1) International, which is comprised of property, casualty and specialty insurance and reinsurance classes of business originating from the Company’s London, Dublin, and Hamilton Select operations; and (2) Bermuda, which is comprised of property, casualty and specialty insurance and reinsurance classes of business originating from Hamilton Re, Bermuda and Hamilton Re US and subsidiaries. We consider many factors, including the nature of each segment’s products, client types, production sources, distribution methods and the regulatory environment, in determining the aggregated operating segments. Corporate includes net realized and unrealized gains (losses) on investments, net investment income (loss), other income (loss) not incurred by the reportable segments, net foreign exchange gains (losses), general and administrative expenses not incurred by the reportable segments, amortization of intangible assets, interest expense, and income tax expense. (Expressed in thousands of U.S. Dollars) Three Months Ended September 30, 2023 International Bermuda Corporate Total Gross premiums written $ 307,140 $ 166,983 $ — $ 474,123 Net premiums written $ 234,621 $ 148,945 $ — $ 383,566 Net premiums earned $ 178,632 $ 158,404 $ — $ 337,036 Third party fee income 2,115 186 — 2,301 Losses and loss adjustment expenses 97,820 93,757 — 191,577 Acquisition costs 47,236 31,301 — 78,537 Other underwriting expenses 31,634 12,723 — 44,357 Underwriting income (loss) $ 4,057 $ 20,809 $ — $ 24,866 Net realized and unrealized gains (losses) on investments 47,343 47,343 Net investment income (loss) 8,069 8,069 Other income (loss), excluding third party fee income 85 85 Net foreign exchange gains (losses) 1,432 1,432 Corporate expenses (18,678) (18,678) Amortization of intangible assets (2,794) (2,794) Interest expense (5,288) (5,288) Net income (loss) before tax 55,035 Income tax expense (2,387) (2,387) Net income (loss) 52,648 Net income (loss) attributable to non-controlling interest 9,065 9,065 Net income (loss) attributable to common shareholders $ 43,583 Key Ratios Attritional loss ratio - current year 54.6 % 55.1 % 54.8 % Attritional loss ratio - prior year development (5.3) % 5.7 % (0.1) % Catastrophe loss ratio - current year 5.1 % 2.6 % 3.9 % Catastrophe loss ratio - prior year development 0.4 % (4.2) % (1.8) % Loss and loss adjustment expense ratio 54.8 % 59.2 % 56.8 % Acquisition cost ratio 26.4 % 19.8 % 23.3 % Other underwriting expense ratio 16.5 % 7.9 % 12.5 % Combined ratio 97.7 % 86.9 % 92.6 % (Expressed in thousands of U.S. Dollars) Three Months Ended September 30, 2022 International Bermuda Corporate Total Gross premiums written $ 269,228 $ 131,583 $ — $ 400,811 Net premiums written $ 184,319 $ 116,492 $ — $ 300,811 Net premiums earned $ 156,307 $ 138,636 $ — $ 294,943 Third party fee income 3,138 106 — 3,244 Losses and loss adjustment expenses 92,061 165,902 — 257,963 Acquisition costs 41,936 23,799 — 65,735 Other underwriting expenses 26,811 13,753 — 40,564 Underwriting income (loss) $ (1,363) $ (64,712) $ — $ (66,075) Net realized and unrealized gains (losses) on investments (67,380) (67,380) Net investment income (loss) (5,255) (5,255) Other income (loss), excluding third party fee income (517) (517) Net foreign exchange gains (losses) 1,906 1,906 Corporate expenses (5,780) (5,780) Amortization of intangible assets (3,178) (3,178) Interest expense (4,102) (4,102) Net income (loss) before tax (150,381) Income tax expense (1,054) (1,054) Net income (loss) (151,435) Net income (loss) attributable to non-controlling interest (15,318) (15,318) Net income (loss) attributable to common shareholders $ (136,117) Key Ratios Attritional loss ratio - current year 46.7 % 53.0 % 49.6 % Attritional loss ratio - prior year development (0.1) % 21.7 % 10.2 % Catastrophe loss ratio - current year 11.9 % 46.8 % 28.3 % Catastrophe loss ratio - prior year development 0.4 % (1.8) % (0.6) % Loss and loss adjustment expense ratio 58.9 % 119.7 % 87.5 % Acquisition cost ratio 26.8 % 17.2 % 22.3 % Other underwriting expense ratio 15.2 % 9.8 % 12.7 % Combined ratio 100.9 % 146.7 % 122.5 % (Expressed in thousands of U.S. Dollars) Nine Months Ended September 30, 2023 International Bermuda Corporate Total Gross premiums written $ 832,049 $ 685,198 $ — $ 1,517,247 Net premiums written $ 553,687 $ 563,085 $ — $ 1,116,772 Net premiums earned $ 504,784 $ 447,614 $ — $ 952,398 Third party fee income 7,417 336 — 7,753 Losses and loss adjustment expenses 255,787 263,767 — 519,554 Acquisition costs 131,688 88,844 — 220,532 Other underwriting expenses 89,635 36,607 — 126,242 Underwriting income (loss) $ 35,091 $ 58,732 $ — $ 93,823 Net realized and unrealized gains (losses) on investments 101,881 101,881 Net investment income (loss) 17,719 17,719 Other income (loss), excluding third party fee income 85 85 Net foreign exchange gains (losses) (3,953) (3,953) Corporate expenses (31,833) (31,833) Amortization of intangible assets (7,869) (7,869) Interest expense (16,007) (16,007) Net income (loss) before tax 153,846 Income tax expense (6,908) (6,908) Net income (loss) 146,938 Net income (loss) attributable to non-controlling interest 15,076 15,076 Net income (loss) attributable to common shareholders $ 131,862 Key Ratios Attritional loss ratio - current year 52.6 % 50.8 % 51.8 % Attritional loss ratio - prior year development (4.3) % 4.0 % (0.4) % Catastrophe loss ratio - current year 2.2 % 5.4 % 3.7 % Catastrophe loss ratio - prior year development 0.2 % (1.3) % (0.5) % Loss and loss adjustment expense ratio 50.7 % 58.9 % 54.6 % Acquisition cost ratio 26.1 % 19.8 % 23.2 % Other underwriting expense ratio 16.3 % 8.1 % 12.4 % Combined ratio 93.1 % 86.8 % 90.2 % (Expressed in thousands of U.S. Dollars) Nine Months Ended September 30, 2022 International Bermuda Corporate Total Gross premiums written $ 698,968 $ 606,453 $ — $ 1,305,421 Net premiums written $ 446,577 $ 491,911 $ — $ 938,488 Net premiums earned $ 450,202 $ 381,265 $ — $ 831,467 Third party fee income 9,022 355 — 9,377 Losses and loss adjustment expenses 249,840 347,174 — 597,014 Acquisition costs 122,593 72,202 — 194,795 Other underwriting expenses 82,256 37,100 — 119,356 Underwriting income (loss) $ 4,535 $ (74,856) $ — $ (70,321) Net realized and unrealized gains (losses) on investments 146,640 146,640 Net investment income (loss) (22,185) (22,185) Other income (loss), excluding third party fee income (260) (260) Net foreign exchange gains (losses) 15,382 15,382 Corporate expenses (15,934) (15,934) Amortization of intangible assets (9,874) (9,874) Interest expense (11,255) (11,255) Net income (loss) before tax 32,193 Income tax expense (3,103) (3,103) Net income (loss) 29,090 Net income (loss) attributable to non-controlling interest 68,069 68,069 Net income (loss) attributable to common shareholders $ (38,979) Key Ratios Attritional loss ratio - current year 47.4 % 52.1 % 49.5 % Attritional loss ratio - prior year development (3.5) % 7.2 % 1.4 % Catastrophe loss ratio - current year 10.5 % 37.0 % 22.7 % Catastrophe loss ratio - prior year development 1.1 % (5.2) % (1.8) % Loss and loss adjustment expense ratio 55.5 % 91.1 % 71.8 % Acquisition cost ratio 27.2 % 18.9 % 23.4 % Other underwriting expense ratio 16.3 % 9.6 % 13.3 % Combined ratio 99.0 % 119.6 % 108.5 % The following table presents gross premiums written by the geographical location of the Company's subsidiaries for the three and nine months ended September 30, 2023 and 2022: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 International Lloyd's of London $ 189,155 $ 145,940 $ 507,326 $ 417,286 Ireland 96,272 110,263 271,002 255,539 U.S. 21,713 13,025 53,721 26,143 Total International 307,140 269,228 832,049 698,968 Bermuda 166,983 131,583 685,198 606,453 Total $ 474,123 $ 400,811 $ 1,517,247 $ 1,305,421

Debt and Credit Facilities

Debt and Credit Facilities	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Debt and Credit Facilities	Debt and Credit Facilities Debt On June 23, 2022, Hamilton Group renewed its unsecured $150 million term loan credit arrangement, as amended from time to time (the "Facility"), with various lenders as arranged by Wells Fargo Securities, LLC. All or a portion of the loan issued under the renegotiated Facility bears interest at either (a) the Base Rate plus the Applicable Margin or (b) the Adjusted Term Secured Overnight Financing Rate ("SOFR") plus the Applicable Margin, at Hamilton Group's discretion. In the event of default, an additional 2% interest in excess of (a) or (b) will be levied, not to exceed the highest rate permissible under applicable law, and certain types of loans may not be available for borrowing by Hamilton Group under the Facility. The Facility matures on June 23, 2025, unless accelerated pursuant to the terms of the Facility, and it contains usual and customary representations, warranties, conditions and covenants for bank loan facilities of this type. The Facility also contains certain financial covenants which cap the ratio of consolidated debt to capital and require that Hamilton Group maintain a certain minimum consolidated net worth. The net worth requirement is recalculated effective as of the end of each fiscal quarter. As of September 30, 2023, the outstanding loan balance was $150.0 million, the fair value was $151.0 million, the unamortized issuance costs were $0.2 million, and the Company was in compliance with all covenants . Debt issuance costs are amortized over the period during which the Facility is outstanding, as an offset to investment income. The Company amortized debt issuance costs of $0.1 million or less in each of the three and nine months ended September 30, 2023 and 2022. The Company’s debt is classified as Level 3 within the fair value hierarchy because it is valued using an income approach, which utilizes a discounted cash flow technique that considers the credit profile of the Company. Credit Facilities The Company has several available letter of credit facilities and a revolving loan facility provided by commercial banks. The letter of credit facilities are utilized to provide collateral to reinsureds of Hamilton Re and its affiliates to the extent required under reinsurance agreements and to support capital requirements at Lloyd’s. On June 23, 2022, Hamilton Group and Hamilton Re amended and restated their unsecured credit agreement with a syndication of lenders (the “Unsecured Facility"). Under the Unsecured Facility, the lenders have agreed to provide up to an aggregate of $415 million of letter of credit capacity for Hamilton Re, up to $150 million of which may be utilized for revolving loans to be issued to Hamilton Group. At September 30, 2023, there were no loan amounts outstanding under this facility. Letters of credit issued under the facility bear interest at a rate of 150 basis points, while revolving loans if issued are subject to a fee of SOFR plus a margin of 185 basis points. To the extent such loans are issued, the available letter of credit capacity shall decrease proportionally, such that the aggregate credit exposure for the lenders under the credit agreement is $415 million. Amounts unutilized under the facility are subject to a fee of 22.5 basis points. Capacity is provided by Wells Fargo, National Association, Truist Bank, BMO Harris Bank N.A., Commerzbank AG, New York Branch, HSBC Bank USA, N. A., and Barclays Bank PLC. Unless renewed or otherwise terminated in accordance with its terms, the Unsecured Facility is scheduled to terminate on June 23, 2025. On August 11, 2023, Hamilton Re and HIDAC amended their committed letter of credit facility agreement with Bank of Montreal ("BMO"), with Hamilton Group as guarantor, under which BMO agreed to make available a secured letter of credit facility of $50 million for a term that will expire on August 13, 2024. The facility bears a fee of 40 basis points for letters of credit issued and 15 basis points on any unutilized portion of the facility. On October 26, 2023, Hamilton Re amended its letter of credit facility agreement with UBS AG ("UBS") under which UBS and certain of its affiliates agreed to make available to Hamilton Re a secured letter of credit facility of $100 million for a term that will expire on October 26, 2024. The facility bears a fee of 140 basis points on the total available capacity. In addition, Hamilton Re is the borrower under a $205 million unsecured letter of credit facility agreement that it utilizes to provide Funds at Lloyd's ("FAL") ("FAL LOC Facility") to support the FAL requirements of Syndicate 4000. Capacity is provided by Barclays Bank PLC, ING Bank N.V., London Branch, and Bank of Montreal, London Branch. The facility bears a fee of 162.5 basis points on the borrowed amount. The FAL LOC Facility was increased to $230 million on October 27, 2023 for an additional one year term that expires on October 27, 2024. The facility fees on the borrowed amount remain the same. The Company’s obligations under its credit facilities require Hamilton Group, Hamilton Re and the other parties thereto to comply with various financial and reporting covenants. All applicable entities were in compliance with all such covenants at September 30, 2023. Certain of the Company's credit facilities are secured by pledged interests in the TS Hamilton Fund, the Company's fixed income security portfolio, or cash. The Company’s credit facilities at September 30, 2023, and associated securities pledged, were as follows: (Expressed in thousands of U.S. Dollars) 2023 Available letter of credit and revolving loan facilities - commitments $ 924,491 Available letter of credit and revolving loan facilities - in use 634,977 Security pledged under letter of credit and revolving loan facilities: Pledged interests in TS Hamilton Fund $ 214,437 Pledged interests in fixed income portfolio 216,696 Cash 6,847 The Company has recognized interest expense related to the above debt and credit facilities of $5.3 million and $4.1 million for the three months ended September 30, 2023 and 2022, respectively, and $16.0 million and $11.3 million for the nine months ended September 30, 2023 and 2022, respectively.

Share Capital

Share Capital	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Share Capital	Share Capital Authorized and Issued Hamilton Group’s share capital at September 30, 2023 and December 31, 2022, is comprised as follows: (Expressed in thousands of U.S. Dollars, except share information) Authorized: 150,000,000 common shares of $0.01 par value each Issued, outstanding and fully paid: 2023 2022 Class A common shares (2023 and 2022: 30,520,078) $ 305 $ 305 Class B common shares (2023: 42,658,302 and 2022: 42,042,155) 427 420 Class C common shares (2023 and 2022: 30,525,626) 305 305 Total $ 1,037 $ 1,030 The following is a summary of the activity related to common shares authorized for the three months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 53,993,690 50,480,684 30,525,626 135,000,000 Increase in authorized share capital — 15,000,000 — 15,000,000 Common shares - end of period 53,993,690 65,480,684 30,525,626 150,000,000 2022 Class A Class B Class C Total Common shares - beginning of period 53,993,690 48,984,123 32,022,187 135,000,000 Share class conversions — 1,496,561 (1,496,561) — Common shares - end of period 53,993,690 50,480,684 30,525,626 135,000,000 The following is a summary of the activity related to common shares authorized for the nine months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 53,993,690 50,480,684 30,525,626 135,000,000 Increase in authorized share capital — 15,000,000 — 15,000,000 Common shares - end of period 53,993,690 65,480,684 30,525,626 150,000,000 2022 Class A Class B Class C Total Common shares - beginning of period 53,793,690 46,898,612 34,307,698 135,000,000 Share class conversions 200,000 3,582,072 (3,782,072) — Common shares - end of period 53,993,690 50,480,684 30,525,626 135,000,000 The following is a summary of the activity related to common shares issued and outstanding for the three months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,638,190 30,525,626 103,683,894 Director share awards granted — 20,112 — 20,112 Common shares - end of period 30,520,078 42,658,302 30,525,626 103,704,006 2022 Class A Class B Class C Total Common shares - beginning of period 30,520,078 40,497,039 32,022,187 103,039,304 Share class conversions — 1,496,561 (1,496,561) — Employee and director share purchases — 22,750 — 22,750 Director share awards granted — 25,805 — 25,805 Common shares - end of period 30,520,078 42,042,155 30,525,626 103,087,859 The following is a summary of the activity related to common shares issued and outstanding for the nine months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,042,155 30,525,626 103,087,859 Vesting of awards — 735,013 — 735,013 Director share awards granted — 44,892 — 44,892 Share repurchases — (163,758) — (163,758) Common shares - end of period 30,520,078 42,658,302 30,525,626 103,704,006 2022 Class A Class B Class C Total Common shares - beginning of period 30,320,078 37,935,266 34,307,698 102,563,042 Share class conversions 200,000 3,582,072 (3,782,072) — Vesting of awards — 580,935 — 580,935 Employee and director share purchases — 22,750 — 22,750 Director share awards granted — 25,805 — 25,805 Share repurchases — (104,673) — (104,673) Common shares - end of period 30,520,078 42,042,155 30,525,626 103,087,859 In general, holders of Class A common shares and Class B common shares have one vote for each common share held while the Class C common shares have no voting rights, except as required by law. However, each holder of Class A common shares and Class B common shares is limited to voting (directly, indirectly or constructively, as determined for U.S. federal income tax purposes) that number of common shares equal to 9.5% of the total combined voting power of all classes of shares of the Company (or, in the case of a class vote by the holders of our Class B common shares, such as in respect of the election or removal of directors other than for directors who are appointed by certain shareholders pursuant to the Shareholders Agreement and our Bye-laws, a maximum of 14.92% of the total combined voting power). In addition, the Board of Directors may limit a shareholder’s voting rights when it deems it appropriate to do so to avoid certain material adverse tax, legal or regulatory consequences to the Company or any direct or indirect shareholder or its affiliates. The Company Bye-laws provide for the redesignation of shares from (i) Class A common shares to Class B common shares automatically upon any transfer, whether or not for value, from (ii) Class B common shares to Class A common shares at the request of a Class A member and upon approval by a Simple Majority of the Board, from (iii) Class A common shares and Class B common shares to Class C common shares at the request of the transferring shareholder and subject to approval by a Simple Majority of the Board and, (iv) from Class C common shares to Class B common shares upon approval by a Simple Majority of the Board. Effective upon listing on the New York Stock Exchange ("NYSE"), the Company Bye-laws provide for the redesignation of shares, as described in (i)-(iv) above, automatically upon transfer. The number of authorized and issued Class A common shares and Class C common shares, as applicable, shall be reduced by the aggregate number of such issued Class A common shares and Class C common shares, as applicable, converted to Class B common shares and the number of authorized and issued Class B common shares shall be correspondingly increased by the same amount. Certain of Hamilton Group’s shareholders that own an aggregate of 62.0 million Class A, Class B and Class C common shares at September 30, 2023 have liquidity rights stipulating that on either December 23, 2023, or at the end of each three-year period thereafter, or upon the occurrence of a Trigger Event (as such term is defined in the Second Amended and Restated Shareholders' Agreement), such shareholders may cause, at the Company’s election, for the Company to either repurchase all or any portion of the exercised common shares held by such shareholder(s) at diluted book value or require an auction for a cash sale of the Company, at the Company's option. For purposes of these liquidity rights a Trigger Event includes any of the following: (i) various adverse tax determinations, including if the Company is determined to be a “passive foreign investment company” for U.S. federal income tax purposes; (ii) various changes in law that have material adverse consequences to either the Company or the applicable shareholders' interests in the Company; (iii) a downgrade in any material subsidiary’s financial strength rating to any level below A- by A.M. Best Company; or (iv) one or more changes in law (including regulatory requirements) that in the aggregate result in (a) a reduction in the investable assets of the Company invested with Two Sigma specifically, or alternative investment managers employing similar strategies generally, such that 75% or less of the Company’s investable assets will be invested with Two Sigma or such alternative investment managers or (b) Two Sigma specifically, or alternative investment managers employing similar strategies generally, being required to adopt a materially different investment strategy with respect to the investable assets of the Company. Should the Company elect to repurchase all or a portion of the common shares held by such exercising shareholder(s), such repurchase is subject to (i) applicable law and (ii) reasonable determination by the Board of Directors that A.M. Best Company will not downgrade or take any ratings action with respect to Hamilton Re’s financial strength rating as a result. Effective upon listing on the NYSE, a new shareholders' agreement was executed between the Company and certain significant shareholders, and the liquidity rights described above no longer apply.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The following table sets forth the computation of basic and diluted income (loss) per common share for the three and nine months ended September 30, 2023 and 2022, respectively: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars, except share information) 2023 2022 2023 2022 Numerator: Net income (loss) attributable to common shareholders $ 43,583 $ (136,117) $ 131,862 $ (38,979) Denominator: Weighted average common shares outstanding - basic 103,704 103,074 103,711 103,053 Effect of dilutive securities 1,720 — 1,260 — Weighted average common shares outstanding - diluted 105,424 103,074 104,971 103,053 Income (loss) per common share - basic: $ 0.42 $ (1.32) $ 1.27 $ (0.38) Income (loss) per common share - diluted: $ 0.41 $ (1.32) $ 1.26 $ (0.38) In the three and nine months ended September 30, 2023, there were no common shares available for issuance under share-based compensation plans that were excluded from the calculation of diluted income (loss) per share because the assumed exercise or issuance of such shares would be anti-dilutive.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Initial Public Offering On November 14, 2023, the Company consummated an initial public offering ("IPO") of its Class B common shares, which are listed on the NYSE. The Company’s net proceeds from the IPO were approximately $80.7 million, after deducting underwriting discounts and specific incremental expenses directly attributable to the IPO. Effective upon the consummation of the IPO, the Second Amended and Restated Shareholders Agreement terminated and the liquidity rights described in Note 11, Share Capital , which were included in the Shareholders Agreement, are no longer applicable. Value Appreciation Pool The IPO qualifies as a Trigger Event as defined in the VAP Plan. As a result, the Underpin (as discussed in Note 6, Value Appreciation Pool ) became effective with a valuation of $5.16 per VAP unit. As of December 5, 2023, there were 9.5 million VAP units issued and outstanding. Warrants Subsequent to September 30, 2023, a total of 342,500 warrants were exercised, resulting in a net issuance of 271,097 Class B shares. At December 5, 2023, 810,000 warrants remain outstanding and fully vested. Share Capital On October 18, 2023, the Company redesignated 23,473,612 authorized Class A shares in excess of the outstanding Class A shares as unclassified. On November 14, 2023, as part of the IPO, 6,250,000 new class B shares were issued and sold by the Company and 8,750,000 existing shares were sold by the Company's shareholders. Of the 8,750,000 existing shares, 5,711,014 were Class A shares or Class C shares that were redesignated as Class B shares upon transfer. On November 22, 2023, as part of the IPO, an additional 1,500,000 existing shares were sold by the Company's shareholders. Of the 1,500,000 existing shares, 1,145,654 were Class A shares or Class C shares that were redesignated as Class B shares upon transfer. The following is a summary of the activity related to common shares authorized for the period October 1, 2023 to December 5, 2023: 2023 Class A Class B Class C Unclassified Total Common shares - beginning of period 53,993,690 65,480,684 30,525,626 — 150,000,000 Share class conversions (25,348,883) 6,856,668 (4,981,397) 23,473,612 — Common shares - end of period 28,644,807 72,337,352 25,544,229 23,473,612 150,000,000 The following is a summary of the activity related to common shares issued and outstanding for the period October 1, 2023 to December 5, 2023: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,658,302 30,525,626 103,704,006 IPO shares issued — 6,250,000 — 6,250,000 Share class conversions (1,875,271) 6,856,668 (4,981,397) — Exercise of warrants — 271,097 — 271,097 Common shares - end of period 28,644,807 56,036,067 25,544,229 110,225,103 Related Party Transactions Antonio Ursano, Jr. has served as a director of the Company since October 15, 2023. Mr. Ursano previously served as the Group Chief Financial Officer of the Company from September 2019 to July 2021. He is also the Managing Partner and Co-Founder of Insurance Advisory Partners LLC. The Company retained Insurance Advisory Partners LLC (“IAP”) to act as financial advisor to us with respect to evaluating various strategic and financial alternatives including any capital raise by us, including the IPO. The Company agreed to pay IAP (i) a quarterly retainer of $30,000 and (ii) a transaction fee of $1.0 million in connection with the IPO. We have also agreed to reimburse IAP on a quarterly basis for all reasonable and documented out-of-pocket expenses incurred in connection with specified matters, and have provided for indemnification of IAP.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
Basis of Presentation	These financial statements include the accounts of Hamilton Group, Hamilton Re, Hamilton U.K. Holdings Limited, Hamilton Select, HMGA Americas, ACML, and TS Hamilton Fund (collectively the "Company"). All significant intercompany transactions and balances have been eliminated on consolidation
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported and disclosed amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The major estimates recorded in the Company’s financial statements include, but are not limited to, premiums written, provisions for estimated future credit losses, the reserve for losses and loss adjustment expenses and the fair value of investments.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02 Leases (as subsequently clarified in various Updates) which updated accounting guidance that applies to any entity that enters into a lease that does not meet certain scope exceptions. The guidance requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous guidance. The Company adopted this guidance in the first quarter of 2022 by recording a gross-up of the balance sheet in recognition of an operating lease liability for future lease payments and the associated right-of-use asset for the right to use the underlying asset over the lease term. This guidance did not have a material impact on the Company’s results of operations, financial position, cash flows or disclosures. In June 2016, the FASB issued ASU 2016-13 Measurement of Credit Losses on Financial Instruments

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Schedule of Fixed Maturity and Short-Term Investments	The Company’s fixed maturity and short-term investments at September 30, 2023 and December 31, 2022 are as follows: 2023 (Expressed in thousands of U.S. Dollars) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities: U.S. government treasuries $ 651,446 $ 21 $ (32,381) $ 619,086 U.S. states, territories and municipalities 4,729 — (375) 4,354 Non-U.S. sovereign governments and supranationals 44,759 413 (1,840) 43,332 Corporate 853,433 81 (42,177) 811,337 Residential mortgage-backed securities - Agency 148,097 — (20,117) 127,980 Residential mortgage-backed securities - Non-agency 4,763 2 (821) 3,944 Commercial mortgage-backed securities - Non-agency 10,188 — (1,295) 8,893 Other asset-backed securities 12,847 15 (317) 12,545 Total fixed maturities 1,730,262 532 (99,323) 1,631,471 Short-term investments 347,623 1,345 — 348,968 Total $ 2,077,885 $ 1,877 $ (99,323) $ 1,980,439 2022 (Expressed in thousands of U.S. Dollars) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities: U.S. government treasuries $ 498,841 $ 99 $ (27,089) $ 471,851 U.S. states, territories and municipalities 4,741 — (434) 4,307 Non-U.S. sovereign governments and supranationals 14,191 363 (1,602) 12,952 Corporate 690,900 363 (43,786) 647,477 Residential mortgage-backed securities - Agency 111,234 — (14,824) 96,410 Residential mortgage-backed securities - Non-agency 5,147 — (772) 4,375 Commercial mortgage-backed securities - Non-agency 10,283 — (1,064) 9,219 Other asset-backed securities 13,347 1 (463) 12,885 Total fixed maturities 1,348,684 826 (90,034) 1,259,476 Short-term investments 285,130 986 (5) 286,111 Total $ 1,633,814 $ 1,812 $ (90,039) $ 1,545,587
Schedule of Contractual Maturities of Fixed Maturity Securities	The following table presents contractual maturities of fixed maturity securities at September 30, 2023. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. 2023 (Expressed in thousands of U.S. Dollars) Amortized Cost Fair Value Due less than one year $ 139,886 $ 135,950 Due after one through five years 1,164,512 1,107,734 Due after five through ten years 245,255 230,867 Due after ten years 4,714 3,558 Mortgage-backed 163,048 140,817 Asset-backed 12,847 12,545 Total $ 1,730,262 $ 1,631,471
Schedule of Investments in Two Sigma Funds	The Company’s investments in Two Sigma Funds at September 30, 2023 and December 31, 2022 are as follows: 2023 2022 (Expressed in thousands of U.S. Dollars) Cost Net Unrealized Gains (Losses) Fair Value Cost Net Unrealized Gains (Losses) Fair Value Two Sigma Futures Portfolio, LLC (FTV) $ 469,379 $ (7,212) $ 462,167 $ 438,625 $ (95,213) $ 343,412 Two Sigma Spectrum Portfolio, LLC (STV) 239,819 54,115 293,934 171,135 57,982 229,117 Two Sigma Equity Spectrum Portfolio, LLC (ESTV) 182,593 41,292 223,885 121,340 46,867 168,207 Total $ 891,791 $ 88,195 $ 979,986 $ 731,100 $ 9,636 $ 740,736
Summary of Certain Investments of FTV, STV and ESTV	The following table summarizes certain investments of FTV, STV and ESTV where TS Hamilton Fund’s proportionate share of the fair value of the investment represents more than 5% of TS Hamilton Fund’s members’ equity at September 30, 2023: 2023 (Expressed in thousands of U.S. Dollars) Principal / Shares (1) Fair Value (1) % of Members' Equity State Street Treasury Obligations Money Market Fund 126,802 $ 126,802 7.5 % U.S. Treasury Securities, 0.0000% - 4.6250%, due 10/5/2023 - 8/15/2043 710,830 $ 704,227 41.5 % U.K. Gilt Securities, 1.6250%, due 10/22/2028 604 $ 650 — % U.K. Gilt Securities, 3.2500% - 3.7500%, due 1/31/2033 - 10/22/2053 (82,909) $ (89,773) (5.3) % U.S. Treasury Securities, 3.8750% - 5.0000%, due 9/30/2025 - 8/15/2023 (240,013) $ (236,195) (13.9) % (1)
Schedule of Realized and Unrealized Gains (Losses) on Investments and Net Investment Income (Loss)	The components of total realized and unrealized gains (losses) on investments and net investment income (loss) for the three and nine months ended September 30, 2023 and 2022 are as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Net realized and unrealized gains (losses) on investments: Net realized gains (losses) on investments $ 42,403 $ 115,129 $ 32,363 $ 267,140 Change in net unrealized gains (losses) on investments 4,940 (182,509) 69,518 (120,500) Net realized and unrealized gains (losses) on investments 47,343 (67,380) 101,881 146,640 Net investment income (loss): Fixed maturities 12,208 5,880 31,178 14,343 Short-term investments 38 334 287 737 TS Hamilton Fund 3,121 3,095 13,033 4,603 Cash and cash equivalents 4,029 544 8,752 696 Other (104) (431) 1,015 (1,230) Interest and other 19,292 9,422 54,265 19,149 Management fees (10,958) (14,420) (35,806) (40,601) Other expenses (265) (257) (740) (733) Net investment income (loss) 8,069 (5,255) 17,719 (22,185) Total realized and unrealized gains (losses) on investments and net investment income (loss) $ 55,412 $ (72,635) $ 119,600 $ 124,455 `
Schedule of Realized Gain (Loss) on Investments	The components of net realized gains (losses) on investments for the three and nine months ended September 30, 2023 and 2022 are as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Fixed maturities and short-term investments $ (7,688) $ (3,313) $ (10,796) $ (13,684) TS Hamilton Fund 50,091 118,442 42,948 279,977 Other — — 211 847 Net realized gains (losses) on investments $ 42,403 $ 115,129 $ 32,363 $ 267,140
Schedule of Unrealized Gain (Loss) on Investments	The components of net unrealized gains (losses) on investments for the three and nine months ended September 30, 2023 and 2022 are as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Fixed maturities and short-term investments $ (12,818) $ (38,556) $ (9,800) $ (101,760) TS Hamilton Fund 17,758 (143,953) 79,318 (18,740) Net realized gains (losses) on investments $ 4,940 $ (182,509) $ 69,518 $ (120,500)

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments Measured at Fair Value on a Recurring Basis	The following table presents the financial instruments measured at fair value on a recurring basis at September 30, 2023 and December 31, 2022: 2023 (Expressed in thousands of U.S. Dollars) Level 1 Level 2 Level 3 Total Fixed maturities: U.S. government treasuries $ — $ 619,086 $ — $ 619,086 U.S. states, territories and municipalities — 4,354 — 4,354 Non-U.S. sovereign governments and supranationals — 43,332 — 43,332 Corporate — 811,337 — 811,337 Residential mortgage-backed securities - Agency — 127,980 — 127,980 Residential mortgage-backed securities - Non-agency — 3,944 — 3,944 Commercial mortgage-backed securities - Non-agency — 8,893 — 8,893 Other asset-backed securities — 12,545 — 12,545 Total fixed maturities — 1,631,471 — 1,631,471 Short-term investments — 348,968 — 348,968 Total $ — $ 1,980,439 $ — $ 1,980,439 2022 (Expressed in thousands of U.S. Dollars) Level 1 Level 2 Level 3 Total Fixed maturities: U.S. government treasuries $ — $ 471,851 $ — $ 471,851 U.S. states, territories and municipalities — 4,307 — 4,307 Non-U.S. sovereign governments and supranationals — 12,952 — 12,952 Corporate — 647,477 — 647,477 Residential mortgage-backed securities - Agency — 96,410 — 96,410 Residential mortgage-backed securities - Non-agency — 4,375 — 4,375 Commercial mortgage-backed securities - Non-agency — 9,219 — 9,219 Other asset-backed securities — 12,885 — 12,885 Total fixed maturities — 1,259,476 — 1,259,476 Short-term investments — 286,111 — 286,111 Total $ — $ 1,545,587 $ — $ 1,545,587

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Activity In and Total Assets and Total Liabilities of TS Hamilton Fund	Activity in the non-controlling interest of TS Hamilton Fund for the three and nine months ended September 30, 2023 and 2022 was as follows: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 Balance - beginning of period $ 124 $ 15,462 $ 119 $ 124 Withdrawals (9,060) — (15,066) (68,049) Equity in earnings 5 (1) 10 20 Incentive allocation 9,060 (15,317) 15,066 68,049 Balance - end of period $ 129 $ 144 $ 129 $ 144 The following table represents the total assets and total liabilities of TS Hamilton Fund at September 30, 2023 and December 31, 2022. Creditors or beneficial interest holders of TS Hamilton Fund have no recourse to the general credit of the Company as the Company’s obligation is limited to the amount of its committed investment. (Expressed in thousands of U.S. Dollars) 2023 2022 Assets Cash and cash equivalents $ 450,759 $ 800,239 Short-term investments 347,787 264,104 Investments in Two Sigma Funds, at fair value 979,986 740,736 Receivables for investments sold 12,730 — Interest and dividends receivable 804 2,076 Total assets 1,792,066 1,807,155 Liabilities Accounts payable and accrued expenses 254 291 Withdrawal payable 9,060 145,738 Payable for investments purchased 86,933 48,095 Total liabilities 96,247 194,124 Total net assets managed by TS Hamilton Fund $ 1,695,819 $ 1,613,031

Value Appreciation Pool (Tables

Value Appreciation Pool (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Assumptions Used to Value VAP	The aggregate fair value of the VAP was estimated on September 30, 2023 using the following assumptions: Inputs Actual Expected volatility 26.70% Risk-free rate 4.95% Expected life 2.28 years

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2023
Insurance [Abstract]
Schedule of Paid and Unpaid Losses and Loss Adjustment Expenses Recoverable	At September 30, 2023 and December 31, 2022, the distribution of the Company’s paid losses recoverable and unpaid losses and loss adjustment expenses recoverable as categorized by major rating agencies were as follows: % of total paid and unpaid losses and loss adjustment expenses recoverable Classification September 30, December 31, Collateralized 28.7 % 33.8 % A- or better 70.6 % 65.6 % Below A- 0.7 % 0.6 % Total 100.0 % 100.0 %

Reserve for Losses and Loss A_2

Reserve for Losses and Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2023
Insurance [Abstract]
Schedule of Reconciliation of Unpaid Losses and Loss Adjustment Expenses	The following table presents a reconciliation of unpaid losses and loss adjustment expenses ("LAE") for the nine months ended September 30, 2023 and 2022: (Expressed in thousands of U.S. Dollars) 2023 2022 Gross unpaid losses and loss expenses, beginning of period $ 2,856,275 $ 2,415,491 Reinsurance recoverable on unpaid losses 1,177,863 1,112,543 Net unpaid losses and loss expenses, beginning of period 1,678,412 1,302,948 Net losses and loss expenses incurred in respect of losses occurring in: Current year 528,457 600,536 Prior years (8,903) (3,522) Total incurred 519,554 597,014 Net losses and loss expenses paid in respect of losses occurring in: Current year 28,521 18,901 Prior years 397,407 236,661 Total paid 425,928 255,562 Foreign currency revaluation and other 19,661 (39,331) Net unpaid losses and loss expenses, end of period 1,791,699 1,605,069 Reinsurance recoverable on unpaid losses 1,157,123 1,151,128 Gross unpaid losses and loss expenses, end of period $ 2,948,822 $ 2,756,197

Segment Reporting (Tables)

Segment Reporting (Tables)	9 Months Ended
	Sep. 30, 2023
Segment Reporting [Abstract]
Schedule of Segment Reporting Information	(Expressed in thousands of U.S. Dollars) Three Months Ended September 30, 2023 International Bermuda Corporate Total Gross premiums written $ 307,140 $ 166,983 $ — $ 474,123 Net premiums written $ 234,621 $ 148,945 $ — $ 383,566 Net premiums earned $ 178,632 $ 158,404 $ — $ 337,036 Third party fee income 2,115 186 — 2,301 Losses and loss adjustment expenses 97,820 93,757 — 191,577 Acquisition costs 47,236 31,301 — 78,537 Other underwriting expenses 31,634 12,723 — 44,357 Underwriting income (loss) $ 4,057 $ 20,809 $ — $ 24,866 Net realized and unrealized gains (losses) on investments 47,343 47,343 Net investment income (loss) 8,069 8,069 Other income (loss), excluding third party fee income 85 85 Net foreign exchange gains (losses) 1,432 1,432 Corporate expenses (18,678) (18,678) Amortization of intangible assets (2,794) (2,794) Interest expense (5,288) (5,288) Net income (loss) before tax 55,035 Income tax expense (2,387) (2,387) Net income (loss) 52,648 Net income (loss) attributable to non-controlling interest 9,065 9,065 Net income (loss) attributable to common shareholders $ 43,583 Key Ratios Attritional loss ratio - current year 54.6 % 55.1 % 54.8 % Attritional loss ratio - prior year development (5.3) % 5.7 % (0.1) % Catastrophe loss ratio - current year 5.1 % 2.6 % 3.9 % Catastrophe loss ratio - prior year development 0.4 % (4.2) % (1.8) % Loss and loss adjustment expense ratio 54.8 % 59.2 % 56.8 % Acquisition cost ratio 26.4 % 19.8 % 23.3 % Other underwriting expense ratio 16.5 % 7.9 % 12.5 % Combined ratio 97.7 % 86.9 % 92.6 % (Expressed in thousands of U.S. Dollars) Three Months Ended September 30, 2022 International Bermuda Corporate Total Gross premiums written $ 269,228 $ 131,583 $ — $ 400,811 Net premiums written $ 184,319 $ 116,492 $ — $ 300,811 Net premiums earned $ 156,307 $ 138,636 $ — $ 294,943 Third party fee income 3,138 106 — 3,244 Losses and loss adjustment expenses 92,061 165,902 — 257,963 Acquisition costs 41,936 23,799 — 65,735 Other underwriting expenses 26,811 13,753 — 40,564 Underwriting income (loss) $ (1,363) $ (64,712) $ — $ (66,075) Net realized and unrealized gains (losses) on investments (67,380) (67,380) Net investment income (loss) (5,255) (5,255) Other income (loss), excluding third party fee income (517) (517) Net foreign exchange gains (losses) 1,906 1,906 Corporate expenses (5,780) (5,780) Amortization of intangible assets (3,178) (3,178) Interest expense (4,102) (4,102) Net income (loss) before tax (150,381) Income tax expense (1,054) (1,054) Net income (loss) (151,435) Net income (loss) attributable to non-controlling interest (15,318) (15,318) Net income (loss) attributable to common shareholders $ (136,117) Key Ratios Attritional loss ratio - current year 46.7 % 53.0 % 49.6 % Attritional loss ratio - prior year development (0.1) % 21.7 % 10.2 % Catastrophe loss ratio - current year 11.9 % 46.8 % 28.3 % Catastrophe loss ratio - prior year development 0.4 % (1.8) % (0.6) % Loss and loss adjustment expense ratio 58.9 % 119.7 % 87.5 % Acquisition cost ratio 26.8 % 17.2 % 22.3 % Other underwriting expense ratio 15.2 % 9.8 % 12.7 % Combined ratio 100.9 % 146.7 % 122.5 % (Expressed in thousands of U.S. Dollars) Nine Months Ended September 30, 2023 International Bermuda Corporate Total Gross premiums written $ 832,049 $ 685,198 $ — $ 1,517,247 Net premiums written $ 553,687 $ 563,085 $ — $ 1,116,772 Net premiums earned $ 504,784 $ 447,614 $ — $ 952,398 Third party fee income 7,417 336 — 7,753 Losses and loss adjustment expenses 255,787 263,767 — 519,554 Acquisition costs 131,688 88,844 — 220,532 Other underwriting expenses 89,635 36,607 — 126,242 Underwriting income (loss) $ 35,091 $ 58,732 $ — $ 93,823 Net realized and unrealized gains (losses) on investments 101,881 101,881 Net investment income (loss) 17,719 17,719 Other income (loss), excluding third party fee income 85 85 Net foreign exchange gains (losses) (3,953) (3,953) Corporate expenses (31,833) (31,833) Amortization of intangible assets (7,869) (7,869) Interest expense (16,007) (16,007) Net income (loss) before tax 153,846 Income tax expense (6,908) (6,908) Net income (loss) 146,938 Net income (loss) attributable to non-controlling interest 15,076 15,076 Net income (loss) attributable to common shareholders $ 131,862 Key Ratios Attritional loss ratio - current year 52.6 % 50.8 % 51.8 % Attritional loss ratio - prior year development (4.3) % 4.0 % (0.4) % Catastrophe loss ratio - current year 2.2 % 5.4 % 3.7 % Catastrophe loss ratio - prior year development 0.2 % (1.3) % (0.5) % Loss and loss adjustment expense ratio 50.7 % 58.9 % 54.6 % Acquisition cost ratio 26.1 % 19.8 % 23.2 % Other underwriting expense ratio 16.3 % 8.1 % 12.4 % Combined ratio 93.1 % 86.8 % 90.2 % (Expressed in thousands of U.S. Dollars) Nine Months Ended September 30, 2022 International Bermuda Corporate Total Gross premiums written $ 698,968 $ 606,453 $ — $ 1,305,421 Net premiums written $ 446,577 $ 491,911 $ — $ 938,488 Net premiums earned $ 450,202 $ 381,265 $ — $ 831,467 Third party fee income 9,022 355 — 9,377 Losses and loss adjustment expenses 249,840 347,174 — 597,014 Acquisition costs 122,593 72,202 — 194,795 Other underwriting expenses 82,256 37,100 — 119,356 Underwriting income (loss) $ 4,535 $ (74,856) $ — $ (70,321) Net realized and unrealized gains (losses) on investments 146,640 146,640 Net investment income (loss) (22,185) (22,185) Other income (loss), excluding third party fee income (260) (260) Net foreign exchange gains (losses) 15,382 15,382 Corporate expenses (15,934) (15,934) Amortization of intangible assets (9,874) (9,874) Interest expense (11,255) (11,255) Net income (loss) before tax 32,193 Income tax expense (3,103) (3,103) Net income (loss) 29,090 Net income (loss) attributable to non-controlling interest 68,069 68,069 Net income (loss) attributable to common shareholders $ (38,979) Key Ratios Attritional loss ratio - current year 47.4 % 52.1 % 49.5 % Attritional loss ratio - prior year development (3.5) % 7.2 % 1.4 % Catastrophe loss ratio - current year 10.5 % 37.0 % 22.7 % Catastrophe loss ratio - prior year development 1.1 % (5.2) % (1.8) % Loss and loss adjustment expense ratio 55.5 % 91.1 % 71.8 % Acquisition cost ratio 27.2 % 18.9 % 23.4 % Other underwriting expense ratio 16.3 % 9.6 % 13.3 % Combined ratio 99.0 % 119.6 % 108.5 %
Summary of Revenue from External Customers by Geographic Areas	The following table presents gross premiums written by the geographical location of the Company's subsidiaries for the three and nine months ended September 30, 2023 and 2022: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars) 2023 2022 2023 2022 International Lloyd's of London $ 189,155 $ 145,940 $ 507,326 $ 417,286 Ireland 96,272 110,263 271,002 255,539 U.S. 21,713 13,025 53,721 26,143 Total International 307,140 269,228 832,049 698,968 Bermuda 166,983 131,583 685,198 606,453 Total $ 474,123 $ 400,811 $ 1,517,247 $ 1,305,421

Debt and Credit Facilities (Tab

Debt and Credit Facilities (Tables)	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Schedule of Credit Facilities	The Company’s credit facilities at September 30, 2023, and associated securities pledged, were as follows: (Expressed in thousands of U.S. Dollars) 2023 Available letter of credit and revolving loan facilities - commitments $ 924,491 Available letter of credit and revolving loan facilities - in use 634,977 Security pledged under letter of credit and revolving loan facilities: Pledged interests in TS Hamilton Fund $ 214,437 Pledged interests in fixed income portfolio 216,696 Cash 6,847

Share Capital (Tables)

Share Capital (Tables)	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Schedule of Share Capital	Hamilton Group’s share capital at September 30, 2023 and December 31, 2022, is comprised as follows: (Expressed in thousands of U.S. Dollars, except share information) Authorized: 150,000,000 common shares of $0.01 par value each Issued, outstanding and fully paid: 2023 2022 Class A common shares (2023 and 2022: 30,520,078) $ 305 $ 305 Class B common shares (2023: 42,658,302 and 2022: 42,042,155) 427 420 Class C common shares (2023 and 2022: 30,525,626) 305 305 Total $ 1,037 $ 1,030
Schedule of Activity Related to Common Shares	The following is a summary of the activity related to common shares authorized for the three months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 53,993,690 50,480,684 30,525,626 135,000,000 Increase in authorized share capital — 15,000,000 — 15,000,000 Common shares - end of period 53,993,690 65,480,684 30,525,626 150,000,000 2022 Class A Class B Class C Total Common shares - beginning of period 53,993,690 48,984,123 32,022,187 135,000,000 Share class conversions — 1,496,561 (1,496,561) — Common shares - end of period 53,993,690 50,480,684 30,525,626 135,000,000 The following is a summary of the activity related to common shares authorized for the nine months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 53,993,690 50,480,684 30,525,626 135,000,000 Increase in authorized share capital — 15,000,000 — 15,000,000 Common shares - end of period 53,993,690 65,480,684 30,525,626 150,000,000 2022 Class A Class B Class C Total Common shares - beginning of period 53,793,690 46,898,612 34,307,698 135,000,000 Share class conversions 200,000 3,582,072 (3,782,072) — Common shares - end of period 53,993,690 50,480,684 30,525,626 135,000,000 The following is a summary of the activity related to common shares issued and outstanding for the three months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,638,190 30,525,626 103,683,894 Director share awards granted — 20,112 — 20,112 Common shares - end of period 30,520,078 42,658,302 30,525,626 103,704,006 2022 Class A Class B Class C Total Common shares - beginning of period 30,520,078 40,497,039 32,022,187 103,039,304 Share class conversions — 1,496,561 (1,496,561) — Employee and director share purchases — 22,750 — 22,750 Director share awards granted — 25,805 — 25,805 Common shares - end of period 30,520,078 42,042,155 30,525,626 103,087,859 The following is a summary of the activity related to common shares issued and outstanding for the nine months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,042,155 30,525,626 103,087,859 Vesting of awards — 735,013 — 735,013 Director share awards granted — 44,892 — 44,892 Share repurchases — (163,758) — (163,758) Common shares - end of period 30,520,078 42,658,302 30,525,626 103,704,006 2022 Class A Class B Class C Total Common shares - beginning of period 30,320,078 37,935,266 34,307,698 102,563,042 Share class conversions 200,000 3,582,072 (3,782,072) — Vesting of awards — 580,935 — 580,935 Employee and director share purchases — 22,750 — 22,750 Director share awards granted — 25,805 — 25,805 Share repurchases — (104,673) — (104,673) Common shares - end of period 30,520,078 42,042,155 30,525,626 103,087,859 The following is a summary of the activity related to common shares authorized for the period October 1, 2023 to December 5, 2023: 2023 Class A Class B Class C Unclassified Total Common shares - beginning of period 53,993,690 65,480,684 30,525,626 — 150,000,000 Share class conversions (25,348,883) 6,856,668 (4,981,397) 23,473,612 — Common shares - end of period 28,644,807 72,337,352 25,544,229 23,473,612 150,000,000 The following is a summary of the activity related to common shares issued and outstanding for the period October 1, 2023 to December 5, 2023: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,658,302 30,525,626 103,704,006 IPO shares issued — 6,250,000 — 6,250,000 Share class conversions (1,875,271) 6,856,668 (4,981,397) — Exercise of warrants — 271,097 — 271,097 Common shares - end of period 28,644,807 56,036,067 25,544,229 110,225,103

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Income (Loss) per Common Share	The following table sets forth the computation of basic and diluted income (loss) per common share for the three and nine months ended September 30, 2023 and 2022, respectively: Three Months Ended Nine Months Ended September 30, September 30, (Expressed in thousands of U.S. Dollars, except share information) 2023 2022 2023 2022 Numerator: Net income (loss) attributable to common shareholders $ 43,583 $ (136,117) $ 131,862 $ (38,979) Denominator: Weighted average common shares outstanding - basic 103,704 103,074 103,711 103,053 Effect of dilutive securities 1,720 — 1,260 — Weighted average common shares outstanding - diluted 105,424 103,074 104,971 103,053 Income (loss) per common share - basic: $ 0.42 $ (1.32) $ 1.27 $ (0.38) Income (loss) per common share - diluted: $ 0.41 $ (1.32) $ 1.26 $ (0.38)

Subsequent Events (Tables)

Subsequent Events (Tables)	9 Months Ended
	Sep. 30, 2023
Subsequent Events [Abstract]
Schedule of Activity Related to Common Shares	The following is a summary of the activity related to common shares authorized for the three months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 53,993,690 50,480,684 30,525,626 135,000,000 Increase in authorized share capital — 15,000,000 — 15,000,000 Common shares - end of period 53,993,690 65,480,684 30,525,626 150,000,000 2022 Class A Class B Class C Total Common shares - beginning of period 53,993,690 48,984,123 32,022,187 135,000,000 Share class conversions — 1,496,561 (1,496,561) — Common shares - end of period 53,993,690 50,480,684 30,525,626 135,000,000 The following is a summary of the activity related to common shares authorized for the nine months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 53,993,690 50,480,684 30,525,626 135,000,000 Increase in authorized share capital — 15,000,000 — 15,000,000 Common shares - end of period 53,993,690 65,480,684 30,525,626 150,000,000 2022 Class A Class B Class C Total Common shares - beginning of period 53,793,690 46,898,612 34,307,698 135,000,000 Share class conversions 200,000 3,582,072 (3,782,072) — Common shares - end of period 53,993,690 50,480,684 30,525,626 135,000,000 The following is a summary of the activity related to common shares issued and outstanding for the three months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,638,190 30,525,626 103,683,894 Director share awards granted — 20,112 — 20,112 Common shares - end of period 30,520,078 42,658,302 30,525,626 103,704,006 2022 Class A Class B Class C Total Common shares - beginning of period 30,520,078 40,497,039 32,022,187 103,039,304 Share class conversions — 1,496,561 (1,496,561) — Employee and director share purchases — 22,750 — 22,750 Director share awards granted — 25,805 — 25,805 Common shares - end of period 30,520,078 42,042,155 30,525,626 103,087,859 The following is a summary of the activity related to common shares issued and outstanding for the nine months ended September 30, 2023 and 2022: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,042,155 30,525,626 103,087,859 Vesting of awards — 735,013 — 735,013 Director share awards granted — 44,892 — 44,892 Share repurchases — (163,758) — (163,758) Common shares - end of period 30,520,078 42,658,302 30,525,626 103,704,006 2022 Class A Class B Class C Total Common shares - beginning of period 30,320,078 37,935,266 34,307,698 102,563,042 Share class conversions 200,000 3,582,072 (3,782,072) — Vesting of awards — 580,935 — 580,935 Employee and director share purchases — 22,750 — 22,750 Director share awards granted — 25,805 — 25,805 Share repurchases — (104,673) — (104,673) Common shares - end of period 30,520,078 42,042,155 30,525,626 103,087,859 The following is a summary of the activity related to common shares authorized for the period October 1, 2023 to December 5, 2023: 2023 Class A Class B Class C Unclassified Total Common shares - beginning of period 53,993,690 65,480,684 30,525,626 — 150,000,000 Share class conversions (25,348,883) 6,856,668 (4,981,397) 23,473,612 — Common shares - end of period 28,644,807 72,337,352 25,544,229 23,473,612 150,000,000 The following is a summary of the activity related to common shares issued and outstanding for the period October 1, 2023 to December 5, 2023: 2023 Class A Class B Class C Total Common shares - beginning of period 30,520,078 42,658,302 30,525,626 103,704,006 IPO shares issued — 6,250,000 — 6,250,000 Share class conversions (1,875,271) 6,856,668 (4,981,397) — Exercise of warrants — 271,097 — 271,097 Common shares - end of period 28,644,807 56,036,067 25,544,229 110,225,103

Organization (Details)

Organization (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Jul. 01, 2023	Jun. 30, 2023
Related Party
Schedule of Equity Method Investments [Line Items]
Risk transfer capacity	$ 150
Two Sigma Hamilton Fund, LLC | Hamilton Re
Schedule of Equity Method Investments [Line Items]
Commitment for investment in Two Sigma Funds		$ 1,800
Investment in Two Sigma Funds, as a percentage of net tangible assets		60%	95%

Investments - Schedule of Fixed

Investments - Schedule of Fixed Maturity and Short-Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 2,077,885	$ 1,633,814
Gross Unrealized Gains	1,877	1,812
Gross Unrealized Losses	(99,323)	(90,039)
Investments, at fair value	1,980,439	1,545,587
U.S. government treasuries
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	651,446	498,841
Gross Unrealized Gains	21	99
Gross Unrealized Losses	(32,381)	(27,089)
Investments, at fair value	619,086	471,851
U.S. states, territories and municipalities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	4,729	4,741
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(375)	(434)
Investments, at fair value	4,354	4,307
Non-U.S. sovereign governments and supranationals
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	44,759	14,191
Gross Unrealized Gains	413	363
Gross Unrealized Losses	(1,840)	(1,602)
Investments, at fair value	43,332	12,952
Corporate
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	853,433	690,900
Gross Unrealized Gains	81	363
Gross Unrealized Losses	(42,177)	(43,786)
Investments, at fair value	811,337	647,477
Residential mortgage-backed securities - Agency
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	148,097	111,234
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(20,117)	(14,824)
Investments, at fair value	127,980	96,410
Residential mortgage-backed securities - Non-agency
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	4,763	5,147
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(821)	(772)
Investments, at fair value	3,944	4,375
Commercial mortgage-backed securities - Non-agency
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	10,188	10,283
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,295)	(1,064)
Investments, at fair value	8,893	9,219
Other asset-backed securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	12,847	13,347
Gross Unrealized Gains	15	1
Gross Unrealized Losses	(317)	(463)
Investments, at fair value	12,545	12,885
Total fixed maturities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,730,262	1,348,684
Gross Unrealized Gains	532	826
Gross Unrealized Losses	(99,323)	(90,034)
Investments, at fair value	1,631,471	1,259,476
Short-term investments
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	347,623	285,130
Gross Unrealized Gains	1,345	986
Gross Unrealized Losses	0	(5)
Investments, at fair value	$ 348,968	$ 286,111

Investments - Summary of Contra

Investments - Summary of Contractual Maturities of Fixed Maturity Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Amortized Cost	$ 2,077,885	$ 1,633,814
Fair Value
Fair Value	1,980,439	1,545,587
Total fixed maturities
Amortized Cost
Amortized Cost	1,730,262	1,348,684
Fair Value
Fair Value	1,631,471	$ 1,259,476
Fixed Maturities, Excluding Mortgage-backed and Asset-backed Securities
Amortized Cost
Due less than one year	139,886
Due after one through five years	1,164,512
Due after five through ten years	245,255
Due after ten years	4,714
Fair Value
Due less than one year	135,950
Due after one through five years	1,107,734
Due after five through ten years	230,867
Due after ten years	3,558
Mortgage-backed
Amortized Cost
Mortgage/Asset-backed	163,048
Fair Value
Mortgage/Asset-backed	140,817
Asset-backed
Amortized Cost
Mortgage/Asset-backed	12,847
Fair Value
Mortgage/Asset-backed	$ 12,545

Investments - Schedule of Inves

Investments - Schedule of Investments in Two Sigma Funds (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Marketable Securities [Line Items]
Cost	$ 891,791	$ 731,100
Investments in Two Sigma Funds, at fair value	979,986	740,736
Two Sigma Funds
Marketable Securities [Line Items]
Net Unrealized Gains (Losses)	88,195	9,636
Investments in Two Sigma Funds, at fair value	979,986	740,736
Two Sigma Futures Portfolio, LLC (FTV)
Marketable Securities [Line Items]
Cost	469,379	438,625
Net Unrealized Gains (Losses)	(7,212)	(95,213)
Investments in Two Sigma Funds, at fair value	462,167	343,412
Two Sigma Spectrum Portfolio, LLC (STV)
Marketable Securities [Line Items]
Cost	239,819	171,135
Net Unrealized Gains (Losses)	54,115	57,982
Investments in Two Sigma Funds, at fair value	293,934	229,117
Two Sigma Equity Spectrum Portfolio, LLC (ESTV)
Marketable Securities [Line Items]
Cost	182,593	121,340
Net Unrealized Gains (Losses)	41,292	46,867
Investments in Two Sigma Funds, at fair value	$ 223,885	$ 168,207

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended	9 Months Ended
	Jul. 01, 2023	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Management fees		$ 10,958	$ 14,420		$ 35,806	$ 40,601
Restricted cash and cash equivalents		98,979			98,979		$ 130,783
Cash, cash equivalents and restricted cash		903,527	1,352,256		903,527	1,352,256	1,207,203	$ 964,126
Cash and cash equivalents		804,548			804,548		1,076,420
Capital Requirements | Asset Pledged as Collateral
Net Investment Income [Line Items]
Investments, fair value		226,900			226,900		274,000
Restricted cash and cash equivalents		1,800			1,800		2,100
Trust Accounts | Asset Pledged as Collateral
Net Investment Income [Line Items]
Investments, fair value		54,100			54,100		39,000
Restricted cash and cash equivalents		1,400			1,400		1,300
Underwriting Obligations | Asset Pledged as Collateral
Net Investment Income [Line Items]
Investments, fair value		34,900			34,900		0
Restricted cash and cash equivalents		95,500			95,500		126,800
Escrow Funds | Asset Pledged as Collateral
Net Investment Income [Line Items]
Restricted cash and cash equivalents		300			300		600
TS Hamilton Fund
Net Investment Income [Line Items]
Management fee percentage	2.50%			3%
Management fees		10,400	14,000		34,400	39,500
Incentive allocation	30%
Incentive allocation, reduction (as a percent)	50%
Incentive allocation, cumulative net profits (as a percent)	200%
Incentive allocation, excess profits (as a percent)	25%			20%
Incentive allocation, net profits (as a percent)	10%			15%
Incentive allocation		9,100	$ (15,300)		15,100	$ 68,000
Cash and cash equivalents		$ 450,759			$ 450,759		$ 800,239
TS Hamilton Fund | Hamilton Re
Net Investment Income [Line Items]
Initial term		3 years			3 years
Capital account withdrawal, monthly liquidity, number of calendar days prior to month end		15 days			15 days
Capital account withdrawal, daily liquidity, number of business day's written notice		1 day			1 day
Two Sigma Futures Portfolio, LLC (FTV)
Net Investment Income [Line Items]
Percentage of ownership in funds		20.10%			20.10%
Two Sigma Spectrum Portfolio, LLC (STV)
Net Investment Income [Line Items]
Percentage of ownership in funds		16.10%			16.10%
Two Sigma Equity Spectrum Portfolio, LLC (ESTV)
Net Investment Income [Line Items]
Percentage of ownership in funds		8.60%			8.60%
Two Sigma Hamilton Fund, LLC | Hamilton Re
Net Investment Income [Line Items]
Commitment for investment in Two Sigma Funds	$ 1,800,000
Investment in Two Sigma Funds, as a percentage of net tangible assets	60%			95%

Investments - Summary of Certai

Investments - Summary of Certain Investments (Details) - USD ($) shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Net Investment Income [Line Items]
Investments in Two Sigma Funds, at fair value	$ 979,986	$ 740,736
TS Hamilton Fund
Net Investment Income [Line Items]
Investments in Two Sigma Funds, at fair value	$ 979,986	$ 740,736
State Street Treasury Obligations Money Market Fund | TS Hamilton Fund | Long
Net Investment Income [Line Items]
Principal / Shares	126,802
Investments in Two Sigma Funds, at fair value	$ 126,802
State Street Treasury Obligations Money Market Fund | Members' Equity | Investment Concentration Risk | TS Hamilton Fund | Long
Net Investment Income [Line Items]
% of Members' Equity	7.50%
U.K. Gilt Securities, 1.6250%, due 10/22/2028 | TS Hamilton Fund | Long
Net Investment Income [Line Items]
Principal / Shares	604
Investments in Two Sigma Funds, at fair value	$ 650
U.K. Gilt Securities, 1.6250%, due 10/22/2028 | Members' Equity | Investment Concentration Risk | TS Hamilton Fund | Long
Net Investment Income [Line Items]
% of Members' Equity	0%
U.K. Gilt Securities, 3.2500% - 3.7500%, due 1/31/2033 - 10/22/2053 | TS Hamilton Fund | Short
Net Investment Income [Line Items]
Principal / Shares	82,909
Investments in Two Sigma Funds, at fair value	$ 89,773
U.K. Gilt Securities, 3.2500% - 3.7500%, due 1/31/2033 - 10/22/2053 | Members' Equity | Investment Concentration Risk | TS Hamilton Fund | Short
Net Investment Income [Line Items]
% of Members' Equity	5.30%
U.S. Treasury Securities, 0.0000% - 4.6250%, due 10/5/2023 - 8/15/2043 | TS Hamilton Fund | Long
Net Investment Income [Line Items]
Principal / Shares	710,830
Investments in Two Sigma Funds, at fair value	$ 704,227
U.S. Treasury Securities, 0.0000% - 4.6250%, due 10/5/2023 - 8/15/2043 | Members' Equity | Investment Concentration Risk | TS Hamilton Fund | Long
Net Investment Income [Line Items]
% of Members' Equity	41.50%
U.S. Treasury Securities, 3.8750% - 5.0000%, due 9/30/2025 - 8/15/2023 | TS Hamilton Fund | Short
Net Investment Income [Line Items]
Principal / Shares	240,013
Investments in Two Sigma Funds, at fair value	$ 236,195
U.S. Treasury Securities, 3.8750% - 5.0000%, due 9/30/2025 - 8/15/2023 | Members' Equity | Investment Concentration Risk | TS Hamilton Fund | Short
Net Investment Income [Line Items]
% of Members' Equity	13.90%

Investments - Realized and Unre

Investments - Realized and Unrealized Gains (Losses) on Investments and Net Investment Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net realized and unrealized gains (losses) on investments:
Net realized gains (losses) on investments	$ 42,403	$ 115,129	$ 32,363	$ 267,140
Change in net unrealized gains (losses) on investments	4,940	(182,509)	69,518	(120,500)
Net realized and unrealized gains (losses) on investments	47,343	(67,380)	101,881	146,640
Net investment income (loss):
Interest and other	19,292	9,422	54,265	19,149
Management fees	(10,958)	(14,420)	(35,806)	(40,601)
Other expenses	(265)	(257)	(740)	(733)
Net investment income (loss)	8,069	(5,255)	17,719	(22,185)
Total realized and unrealized gains (losses) on investments and net investment income (loss)	55,412	(72,635)	119,600	124,455
Total fixed maturities
Net investment income (loss):
Interest and other	12,208	5,880	31,178	14,343
Short-term investments
Net investment income (loss):
Interest and other	38	334	287	737
TS Hamilton Fund
Net realized and unrealized gains (losses) on investments:
Net realized gains (losses) on investments	50,091	118,442	42,948	279,977
Change in net unrealized gains (losses) on investments	17,758	(143,953)	79,318	(18,740)
Net investment income (loss):
Interest and other	3,121	3,095	13,033	4,603
Cash and cash equivalents
Net investment income (loss):
Interest and other	4,029	544	8,752	696
Other
Net investment income (loss):
Interest and other	(104)	(431)	1,015	(1,230)
Fixed maturities and short-term investments
Net realized and unrealized gains (losses) on investments:
Net realized gains (losses) on investments	(7,688)	(3,313)	(10,796)	(13,684)
Change in net unrealized gains (losses) on investments	(12,818)	(38,556)	(9,800)	(101,760)
Other
Net realized and unrealized gains (losses) on investments:
Net realized gains (losses) on investments	$ 0	$ 0	$ 211	$ 847

Fair Value (Details)

Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	$ 1,980,439	$ 1,545,587
U.S. government treasuries
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	619,086	471,851
U.S. states, territories and municipalities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	4,354	4,307
Non-U.S. sovereign governments and supranationals
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	43,332	12,952
Corporate
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	811,337	647,477
Residential mortgage-backed securities - Agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	127,980	96,410
Residential mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	3,944	4,375
Commercial mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	8,893	9,219
Other asset-backed securities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	12,545	12,885
Total fixed maturities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	1,631,471	1,259,476
Short-term investments
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	348,968	286,111
Level 1
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | U.S. government treasuries
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | U.S. states, territories and municipalities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Non-U.S. sovereign governments and supranationals
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Corporate
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Residential mortgage-backed securities - Agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Residential mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Commercial mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Other asset-backed securities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Total fixed maturities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 1 | Short-term investments
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	1,980,439	1,545,587
Level 2 | U.S. government treasuries
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	619,086	471,851
Level 2 | U.S. states, territories and municipalities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	4,354	4,307
Level 2 | Non-U.S. sovereign governments and supranationals
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	43,332	12,952
Level 2 | Corporate
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	811,337	647,477
Level 2 | Residential mortgage-backed securities - Agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	127,980	96,410
Level 2 | Residential mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	3,944	4,375
Level 2 | Commercial mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	8,893	9,219
Level 2 | Other asset-backed securities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	12,545	12,885
Level 2 | Total fixed maturities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	1,631,471	1,259,476
Level 2 | Short-term investments
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	348,968	286,111
Level 3
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | U.S. government treasuries
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | U.S. states, territories and municipalities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Non-U.S. sovereign governments and supranationals
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Corporate
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Residential mortgage-backed securities - Agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Residential mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Commercial mortgage-backed securities - Non-agency
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Other asset-backed securities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Total fixed maturities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	0	0
Level 3 | Short-term investments
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Investments, at fair value	$ 0	$ 0

Variable Interest Entities - Ac

Variable Interest Entities - Activity in the Non-Controlling Interest (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Equity, Attributable to Noncontrolling Interest [Roll Forward]
Balance - beginning of period			$ 119
Balance - end of period	$ 129		129
TS Hamilton Fund
Equity, Attributable to Noncontrolling Interest [Roll Forward]
Balance - beginning of period	124	$ 15,462	119	$ 124
Withdrawals	(9,060)	0	(15,066)	(68,049)
Equity in earnings	5	(1)	10	20
Incentive allocation	9,060	(15,317)	15,066	68,049
Balance - end of period	$ 129	$ 144	$ 129	$ 144

Variable Interest Entities - To

Variable Interest Entities - Total Assets and Total Liabilities of TS Hamilton Fund (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets
Cash and cash equivalents	$ 804,548	$ 1,076,420
Short-term investments	1,980,439	1,545,587
Investments in Two Sigma Funds, at fair value	979,986	740,736
Receivables for investments sold	19,044	371
Total assets	6,504,604	5,818,965
Liabilities
Accounts payable and accrued expenses	159,681	138,050
Payables for investments purchased	117,836	48,095
Total liabilities	4,704,750	4,154,663
Redemption payable	0	145,700
Short-term investments
Assets
Short-term investments	348,968	286,111
TS Hamilton Fund
Assets
Cash and cash equivalents	450,759	800,239
Investments in Two Sigma Funds, at fair value	979,986	740,736
Receivables for investments sold	12,730	0
Interest and dividends receivable	804	2,076
Total assets	1,792,066	1,807,155
Liabilities
Accounts payable and accrued expenses	254	291
Withdrawal payable	9,060	145,738
Payables for investments purchased	86,933	48,095
Total liabilities	96,247	194,124
Total net assets managed by TS Hamilton Fund	1,695,819	1,613,031
TS Hamilton Fund | Short-term investments
Assets
Short-term investments	$ 347,787	$ 264,104

Value Appreciation Pool - Narra

Value Appreciation Pool - Narrative (Details) - Value Appreciation Pool $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
	Mar. 10, 2023 $ / shares	Sep. 30, 2023 USD ($) shares	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percent of increase in Company fair market value awarded to employees		10%		10%
Units available for issuance (in shares) | shares		10		10
Units issued and outstanding (in shares) | shares		9.5		9.5
Ratio of fair market value to shareholders' equity	1.15
Fair value per VAP unit (in dollars per share) | $ / shares	$ 5
VAP expense | $		$ 11.2		$ 15.6
Share compensation expense | $			$ (4.2)
Maturity Date, 11/30/2025
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting percentage				50%
Maturity Date, 11/30/2026
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting percentage				50%
Vesting upon trigger event, First anniversary
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting percentage				50%
Vesting upon trigger event, Second anniversary
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Vesting percentage				50%

Value Appreciation Pool - Assum

Value Appreciation Pool - Assumptions (Details) - Value Appreciation Pool	9 Months Ended
	Sep. 30, 2023
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected volatility	26.70%
Risk-free rate	4.95%
Expected life	2 years 3 months 10 days

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 06, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Ceded Credit Risk [Line Items]
Premiums receivable balance, credit provisions		$ 2,700		$ 2,700		$ 2,900
Premiums receivable		689,042		689,042		522,670
Paid losses recoverable		138,314		138,314		90,655
Unpaid losses and loss adjustment expenses recoverable		1,157,123	$ 1,151,128	1,157,123	$ 1,151,128	1,177,863	$ 1,112,543
Reinsurance recoverable, provisions		700		700		800
Reinsurance premiums ceded		90,557	100,000	400,475	366,933
Related Party
Ceded Credit Risk [Line Items]
Reinsurance premiums ceded		0	0	7,200	6,300
Risk transfer capacity				150,000
Reinsurance Contract [Axis]: Loss Portfolio Transfer Agreement
Ceded Credit Risk [Line Items]
Unpaid losses and loss adjustment expenses recoverable		50,700		50,700		$ 59,200
Reinsurance premiums ceded	$ 72,100
Amortization of the deferred gain		$ (900)	$ 3,700	$ 2,500	$ 1,700
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable				100%		100%
Reinsurer One | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable				27%		31%
Reinsurer Two | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable				19%		17%
Reinsurer Three | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable				12%		11%

Reinsurance - Schedule of Paid

Reinsurance - Schedule of Paid and Unpaid Losses and Loss Adjustment Expenses Recoverable (Details) - Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments - Reinsurer Concentration Risk	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable	100%	100%
A- or better
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable	70.60%	65.60%
Below A-
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable	0.70%	0.60%
Collateralized
Ceded Credit Risk [Line Items]
% of total paid and unpaid losses and loss adjustment expenses recoverable	28.70%	33.80%

Reserve for Losses and Loss A_3

Reserve for Losses and Loss Adjustment Expenses - Schedule of Reconciliation of Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross unpaid losses and loss expenses, beginning of period			$ 2,856,275	$ 2,415,491
Reinsurance recoverable on unpaid losses			1,177,863	1,112,543
Net unpaid losses and loss expenses, beginning of period			1,678,412	1,302,948
Net losses and loss expenses incurred in respect of losses occurring in:
Current year			528,457	600,536
Prior years			(8,903)	(3,522)
Total incurred	$ 191,577	$ 257,963	519,554	597,014
Net losses and loss expenses paid in respect of losses occurring in:
Current year			28,521	18,901
Prior years			397,407	236,661
Total paid			425,928	255,562
Foreign currency revaluation and other			19,661	(39,331)
Net unpaid losses and loss expenses, end of period	1,791,699	1,605,069	1,791,699	1,605,069
Reinsurance recoverable on unpaid losses	1,157,123	1,151,128	1,157,123	1,151,128
Gross unpaid losses and loss expenses, end of period	$ 2,948,822	$ 2,756,197	$ 2,948,822	$ 2,756,197

Reserve for Losses and Loss A_4

Reserve for Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			$ (8,903)	$ (3,522)
Acquisition costs	$ 78,537	$ 65,735	220,532	194,795
Reserve for losses and loss adjustment expenses	2,948,822	$ 2,756,197	2,948,822	2,756,197	$ 2,856,275	$ 2,415,491
Ukrainian Conflict
Liability for Claims and Claims Adjustment Expense [Line Items]
Reserve for losses and loss adjustment expenses	66,200		66,200		79,300
Covid-19
Liability for Claims and Claims Adjustment Expense [Line Items]
Reserve for losses and loss adjustment expenses	$ 13,900		13,900		$ 39,000
Specialty Contracts
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			(20,300)	(23,600)
Casualty Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			8,800	27,700
Casualty Lines | Reinsurance Contract [Axis]: Loss Portfolio Transfer Agreement
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			(4,000)	(6,000)
Property Contracts
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			6,600	(1,600)
Attritional Losses
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			(4,000)	11,500
Catastrophe Losses
Liability for Claims and Claims Adjustment Expense [Line Items]
Net prior year development, unfavorable (favorable)			$ (4,900)	$ (15,000)

Segment Reporting - Segment Rep

Segment Reporting - Segment Reporting Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) segment	Sep. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			2
Gross premiums written	$ 474,123	$ 400,811	$ 1,517,247	$ 1,305,421
Net premiums written	383,566	300,811	1,116,772	938,488
Net premiums earned	337,036	294,943	952,398	831,467
Third party fee income	2,301	3,244	7,753	9,377
Losses and loss adjustment expenses	191,577	257,963	519,554	597,014
Acquisition costs	78,537	65,735	220,532	194,795
Other underwriting expenses	44,357	40,564	126,242	119,356
Underwriting income (loss)	24,866	(66,075)	93,823	(70,321)
Net realized and unrealized gains (losses) on investments	47,343	(67,380)	101,881	146,640
Net investment income (loss)	8,069	(5,255)	17,719	(22,185)
Other income (loss), excluding third party fee income	85	(517)	85	(260)
Net foreign exchange gains (losses)	1,432	1,906	(3,953)	15,382
Corporate expenses	(18,678)	(5,780)	(31,833)	(15,934)
Amortization of intangible assets	(2,794)	(3,178)	(7,869)	(9,874)
Interest expense	(5,288)	(4,102)	(16,007)	(11,255)
Income (loss) before income tax	55,035	(150,381)	153,846	32,193
Income tax expense	(2,387)	(1,054)	(6,908)	(3,103)
Net income (loss)	52,648	(151,435)	146,938	29,090
Net income (loss) attributable to non-controlling interest	9,065	(15,318)	15,076	68,069
Net income (loss) and other comprehensive income (loss) attributable to common shareholders	$ 43,583	$ (136,117)	$ 131,862	$ (38,979)
Attritional loss ratio - current year	54.80%	49.60%	51.80%	49.50%
Attritional loss ratio - prior year development	(0.10%)	10.20%	(0.40%)	1.40%
Catastrophe loss ratio - current year	3.90%	28.30%	3.70%	22.70%
Catastrophe loss ratio - prior year development	(1.80%)	(0.60%)	(0.50%)	(1.80%)
Loss and loss adjustment expense ratio	56.80%	87.50%	54.60%	71.80%
Acquisition cost ratio	23.30%	22.30%	23.20%	23.40%
Other underwriting expense ratio	12.50%	12.70%	12.40%	13.30%
Combined ratio	92.60%	122.50%	90.20%	108.50%
Operating Segments | International
Segment Reporting Information [Line Items]
Gross premiums written	$ 307,140	$ 269,228	$ 832,049	$ 698,968
Net premiums written	234,621	184,319	553,687	446,577
Net premiums earned	178,632	156,307	504,784	450,202
Third party fee income	2,115	3,138	7,417	9,022
Losses and loss adjustment expenses	97,820	92,061	255,787	249,840
Acquisition costs	47,236	41,936	131,688	122,593
Other underwriting expenses	31,634	26,811	89,635	82,256
Underwriting income (loss)	$ 4,057	$ (1,363)	$ 35,091	$ 4,535
Attritional loss ratio - current year	54.60%	46.70%	52.60%	47.40%
Attritional loss ratio - prior year development	(5.30%)	(0.10%)	(4.30%)	(3.50%)
Catastrophe loss ratio - current year	5.10%	11.90%	2.20%	10.50%
Catastrophe loss ratio - prior year development	0.40%	0.40%	0.20%	1.10%
Loss and loss adjustment expense ratio	54.80%	58.90%	50.70%	55.50%
Acquisition cost ratio	26.40%	26.80%	26.10%	27.20%
Other underwriting expense ratio	16.50%	15.20%	16.30%	16.30%
Combined ratio	97.70%	100.90%	93.10%	99%
Operating Segments | Bermuda
Segment Reporting Information [Line Items]
Gross premiums written	$ 166,983	$ 131,583	$ 685,198	$ 606,453
Net premiums written	148,945	116,492	563,085	491,911
Net premiums earned	158,404	138,636	447,614	381,265
Third party fee income	186	106	336	355
Losses and loss adjustment expenses	93,757	165,902	263,767	347,174
Acquisition costs	31,301	23,799	88,844	72,202
Other underwriting expenses	12,723	13,753	36,607	37,100
Underwriting income (loss)	$ 20,809	$ (64,712)	$ 58,732	$ (74,856)
Attritional loss ratio - current year	55.10%	53%	50.80%	52.10%
Attritional loss ratio - prior year development	5.70%	21.70%	4%	7.20%
Catastrophe loss ratio - current year	2.60%	46.80%	5.40%	37%
Catastrophe loss ratio - prior year development	(4.20%)	(1.80%)	(1.30%)	(5.20%)
Loss and loss adjustment expense ratio	59.20%	119.70%	58.90%	91.10%
Acquisition cost ratio	19.80%	17.20%	19.80%	18.90%
Other underwriting expense ratio	7.90%	9.80%	8.10%	9.60%
Combined ratio	86.90%	146.70%	86.80%	119.60%
Corporate
Segment Reporting Information [Line Items]
Gross premiums written	$ 0	$ 0	$ 0	$ 0
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Third party fee income	0	0	0	0
Losses and loss adjustment expenses	0	0	0	0
Acquisition costs	0	0	0	0
Other underwriting expenses	0	0	0	0
Underwriting income (loss)	0	0	0	0
Net realized and unrealized gains (losses) on investments	47,343	(67,380)	101,881	146,640
Net investment income (loss)	8,069	(5,255)	17,719	(22,185)
Other income (loss), excluding third party fee income	85	(517)	85	(260)
Net foreign exchange gains (losses)	1,432	1,906	(3,953)	15,382
Corporate expenses	(18,678)	(5,780)	(31,833)	(15,934)
Amortization of intangible assets	(2,794)	(3,178)	(7,869)	(9,874)
Interest expense	(5,288)	(4,102)	(16,007)	(11,255)
Income tax expense	(2,387)	(1,054)	(6,908)	(3,103)
Net income (loss) attributable to non-controlling interest	$ 9,065	$ (15,318)	$ 15,076	$ 68,069

Segment Reporting - Summary of

Segment Reporting - Summary of Gross Premiums Written by Geographical Location of Subsidiaries (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	$ 474,123	$ 400,811	$ 1,517,247	$ 1,305,421
Lloyd's of London
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	189,155	145,940	507,326	417,286
Ireland
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	96,272	110,263	271,002	255,539
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	21,713	13,025	53,721	26,143
Total International
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	307,140	269,228	832,049	698,968
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	$ 166,983	$ 131,583	$ 685,198	$ 606,453

Debt and Credit Facilities - Na

Debt and Credit Facilities - Narrative (Details) - USD ($)				3 Months Ended		9 Months Ended
	Oct. 26, 2023	Aug. 11, 2023	Jun. 23, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Nov. 01, 2023
Line of Credit Facility [Line Items]
Line of credit facility, outstanding				$ 634,977,000		$ 634,977,000
Interest expense				5,288,000	$ 4,102,000	16,007,000	$ 11,255,000
Unsecured Debt | Facility
Line of Credit Facility [Line Items]
Face amount			$ 150,000,000
Increase in interest rate in event of default			2%
Outstanding loan balance				150,000,000		150,000,000
Fair value of debt				151,000,000		151,000,000
Unamortized issuance costs				200,000		200,000
Amortization of debt issuance costs				100,000	$ 100,000	100,000	$ 100,000
Line of Credit | Unsecured Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 415,000,000
Line of credit facility, outstanding				0		0
Unused commitment fee percentage			0.225%
Line of Credit | Unsecured Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 150,000,000
Line of Credit | Unsecured Facility | Letter of Credit
Line of Credit Facility [Line Items]
Stated interest rate			1.50%
Line of Credit | Bank of Montreal, Letter of Credit Facility | Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 50,000,000
Unused commitment fee percentage		0.15%
Commitment fee percentage		0.40%
Line of Credit | UBS Letter of Credit Facility | Letter of Credit | Subsequent Event
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 100,000,000
Commitment fee percentage	1.40%
Line of Credit | Unsecured Facility, Lloyd's | Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity				$ 205,000,000		$ 205,000,000
Commitment fee percentage						1.625%
Line of Credit | Unsecured Facility, Lloyd's | Letter of Credit | Subsequent Event
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity								$ 230,000,000
Term of debt agreement								1 year
Secured Overnight Financing Rate (SOFR) | Line of Credit | Unsecured Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.85%

Debt and Credit Facilities - Cr

Debt and Credit Facilities - Credit Facilities (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Line of Credit Facility [Line Items]
Available letter of credit and revolving loan facilities - commitments	$ 924,491
Available letter of credit and revolving loan facilities - in use	634,977
TS Hamilton Fund
Line of Credit Facility [Line Items]
Security pledged under letter of credit and revolving loan facilities:	214,437
Fixed Income Portfolio
Line of Credit Facility [Line Items]
Security pledged under letter of credit and revolving loan facilities:	216,696
Cash
Line of Credit Facility [Line Items]
Security pledged under letter of credit and revolving loan facilities:	$ 6,847

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Common stock authorized (in shares)	150,000,000	135,000,000	135,000,000	135,000,000	135,000,000	135,000,000
Common stock, par value (in dollars per share)	$ 0.01
Common stock issued (in shares)	103,704,006	103,683,894	103,087,859	103,087,859	103,039,304	102,563,042
Common stock outstanding (in shares)	103,704,006	103,683,894	103,087,859	103,087,859	103,039,304	102,563,042
Common shares	$ 1,037		$ 1,030
Common Class A
Class of Stock [Line Items]
Common stock authorized (in shares)	53,993,690	53,993,690	53,993,690	53,993,690	53,993,690	53,793,690
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock issued (in shares)	30,520,078	30,520,078	30,520,078	30,520,078	30,520,078	30,320,078
Common stock outstanding (in shares)	30,520,078	30,520,078	30,520,078	30,520,078	30,520,078	30,320,078
Common shares	$ 305		$ 305
Common Class B
Class of Stock [Line Items]
Common stock authorized (in shares)	65,480,684	50,480,684	50,480,684	50,480,684	48,984,123	46,898,612
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock issued (in shares)	42,658,302	42,638,190	42,042,155	42,042,155	40,497,039	37,935,266
Common stock outstanding (in shares)	42,658,302	42,638,190	42,042,155	42,042,155	40,497,039	37,935,266
Common shares	$ 427		$ 420
Common Class C
Class of Stock [Line Items]
Common stock authorized (in shares)	30,525,626	30,525,626	30,525,626	30,525,626	32,022,187	34,307,698
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock issued (in shares)	30,525,626	30,525,626	30,525,626	30,525,626	32,022,187	34,307,698
Common stock outstanding (in shares)	30,525,626	30,525,626	30,525,626	30,525,626	32,022,187	34,307,698
Common shares	$ 305		$ 305

Share Capital - Schedule of Com

Share Capital - Schedule of Common Stock Authorized (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	135,000,000	135,000,000	135,000,000	135,000,000
Increase in authorized share capital (in shares)	15,000,000		15,000,000
Share class conversions (in shares)		0		0
Common shares - end of period (in shares)	150,000,000	135,000,000	150,000,000	135,000,000
Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	53,993,690	53,993,690	53,993,690	53,793,690
Increase in authorized share capital (in shares)	0		0
Share class conversions (in shares)		0		200,000
Common shares - end of period (in shares)	53,993,690	53,993,690	53,993,690	53,993,690
Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	50,480,684	48,984,123	50,480,684	46,898,612
Increase in authorized share capital (in shares)	15,000,000		15,000,000
Share class conversions (in shares)		1,496,561		3,582,072
Common shares - end of period (in shares)	65,480,684	50,480,684	65,480,684	50,480,684
Common Class C
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	30,525,626	32,022,187	30,525,626	34,307,698
Increase in authorized share capital (in shares)	0		0
Share class conversions (in shares)		(1,496,561)		(3,782,072)
Common shares - end of period (in shares)	30,525,626	30,525,626	30,525,626	30,525,626

Share Capital - Schedule of C_2

Share Capital - Schedule of Common Stock Issued and Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)	103,683,894	103,039,304	103,087,859	102,563,042
Common shares outstanding - beginning of period (in shares)	103,683,894	103,039,304	103,087,859	102,563,042
Share class conversions (in shares)		0		0
Vesting of awards (in shares)			735,013	580,935
Employee and director share purchases (in shares)		22,750		22,750
Director share awards granted (in shares)	20,112	25,805	44,892	25,805
Share repurchases (in shares)			(163,758)	(104,673)
Common shares issued - end of period (in shares)	103,704,006	103,087,859	103,704,006	103,087,859
Common shares outstanding - end of period (in shares)	103,704,006	103,087,859	103,704,006	103,087,859
Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)	30,520,078	30,520,078	30,520,078	30,320,078
Common shares outstanding - beginning of period (in shares)	30,520,078	30,520,078	30,520,078	30,320,078
Share class conversions (in shares)		0		200,000
Vesting of awards (in shares)			0	0
Employee and director share purchases (in shares)		0		0
Director share awards granted (in shares)	0	0	0	0
Share repurchases (in shares)			0	0
Common shares issued - end of period (in shares)	30,520,078	30,520,078	30,520,078	30,520,078
Common shares outstanding - end of period (in shares)	30,520,078	30,520,078	30,520,078	30,520,078
Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)	42,638,190	40,497,039	42,042,155	37,935,266
Common shares outstanding - beginning of period (in shares)	42,638,190	40,497,039	42,042,155	37,935,266
Share class conversions (in shares)		1,496,561		3,582,072
Vesting of awards (in shares)			735,013	580,935
Employee and director share purchases (in shares)		22,750		22,750
Director share awards granted (in shares)	20,112	25,805	44,892	25,805
Share repurchases (in shares)			(163,758)	(104,673)
Common shares issued - end of period (in shares)	42,658,302	42,042,155	42,658,302	42,042,155
Common shares outstanding - end of period (in shares)	42,658,302	42,042,155	42,658,302	42,042,155
Common Class C
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)	30,525,626	32,022,187	30,525,626	34,307,698
Common shares outstanding - beginning of period (in shares)	30,525,626	32,022,187	30,525,626	34,307,698
Share class conversions (in shares)		(1,496,561)		(3,782,072)
Vesting of awards (in shares)			0	0
Employee and director share purchases (in shares)		0		0
Director share awards granted (in shares)	0	0	0	0
Share repurchases (in shares)			0	0
Common shares issued - end of period (in shares)	30,525,626	30,525,626	30,525,626	30,525,626
Common shares outstanding - end of period (in shares)	30,525,626	30,525,626	30,525,626	30,525,626

Share Capital - Narrative (Deta

Share Capital - Narrative (Details) shares in Millions	Sep. 30, 2023 shares
Class of Stock [Line Items]
Percent of combined voting power, Class A and Class B	9.50%
Shares of common stock outstanding with liquidity rights (in shares)	62
Term of liquidity rights	3 years
Percent of investible assets	75%
Common Class B
Class of Stock [Line Items]
Percent of combined voting power, Class A and Class B	14.92%

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net income (loss) attributable to common shareholders	$ 43,583	$ (136,117)	$ 131,862	$ (38,979)
Denominator:
Weighted average common shares outstanding - basic (in shares)	103,704,000	103,074,000	103,711,000	103,053,000
Effect of dilutive securities (in shares)	1,720,000	0	1,260,000	0
Weighted average common shares outstanding - diluted (in shares)	105,424,000	103,074,000	104,971,000	103,053,000
Income (loss) per common share - basic (in dollars per share)	$ 0.42	$ (1.32)	$ 1.27	$ (0.38)
Income (loss) per common share - diluted (in dollars per share)	$ 0.41	$ (1.32)	$ 1.26	$ (0.38)
Anti-dilutive shares excluded from the calculation of diluted income (loss) per share (in shares)	0	3,000,000	0	3,000,000

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands							2 Months Ended	3 Months Ended	9 Months Ended
	Nov. 22, 2023	Nov. 14, 2023	Nov. 10, 2023	Oct. 18, 2023	Oct. 15, 2023	Mar. 10, 2023	Dec. 05, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Subsequent Event [Line Items]
Share class conversions (in shares)								0	0
Value Appreciation Pool
Subsequent Event [Line Items]
Fair value per VAP unit (in dollars per share)						$ 5
Units issued and outstanding (in shares)										9,500,000
Subsequent Event
Subsequent Event [Line Items]
Proceeds from the IPO		$ 80,700
Number of warrants exercised (in shares)							342,500
Number of warrants outstanding (in shares)							810,000
Share class conversions (in shares)							0
Subsequent Event | Value Appreciation Pool
Subsequent Event [Line Items]
Fair value per VAP unit (in dollars per share)			$ 5.16
Units issued and outstanding (in shares)							9,500,000
Subsequent Event | Related Party | Quarterly Retainer
Subsequent Event [Line Items]
Amount of related party transaction					$ 30
Subsequent Event | Related Party | Transaction Fee
Subsequent Event [Line Items]
Amount of related party transaction					$ 1,000
Subsequent Event | IPO
Subsequent Event [Line Items]
Existing shares sold to new shareholders (in shares)	1,500,000		8,750,000
Unclassified common stock | Subsequent Event
Subsequent Event [Line Items]
Share class conversions (in shares)				23,473,612
Common Class B
Subsequent Event [Line Items]
Share class conversions (in shares)								1,496,561	3,582,072
Common Class B | Subsequent Event
Subsequent Event [Line Items]
Number of shares issued through warrant exercised (in shares)							271,097
Share class conversions (in shares)	1,145,654		5,711,014				6,856,668
Common Class B | Subsequent Event | IPO
Subsequent Event [Line Items]
Shares issued in IPO (in shares)			6,250,000

Subsequent Events - Schedule of

Subsequent Events - Schedule of Common Stock Authorized (Details) - shares	2 Months Ended	3 Months Ended	9 Months Ended
	Dec. 05, 2023	Sep. 30, 2022	Sep. 30, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	150,000,000	135,000,000	135,000,000
Share class conversions (in shares)		0	0
Common shares - end of period (in shares)		135,000,000	135,000,000
Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share class conversions (in shares)	0
Common shares - end of period (in shares)	150,000,000
Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	53,993,690	53,993,690	53,793,690
Share class conversions (in shares)		0	200,000
Common shares - end of period (in shares)		53,993,690	53,993,690
Common Class A | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share class conversions (in shares)	(25,348,883)
Common shares - end of period (in shares)	28,644,807
Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	65,480,684	48,984,123	46,898,612
Share class conversions (in shares)		1,496,561	3,582,072
Common shares - end of period (in shares)		50,480,684	50,480,684
Common Class B | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share class conversions (in shares)	6,856,668
Common shares - end of period (in shares)	72,337,352
Common Class C
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	30,525,626	32,022,187	34,307,698
Share class conversions (in shares)		(1,496,561)	(3,782,072)
Common shares - end of period (in shares)		30,525,626	30,525,626
Common Class C | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share class conversions (in shares)	(4,981,397)
Common shares - end of period (in shares)	25,544,229
Unclassified common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares - beginning of period (in shares)	0
Unclassified common stock | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share class conversions (in shares)	23,473,612
Common shares - end of period (in shares)	23,473,612

Subsequent Events - Schedule _2

Subsequent Events - Schedule of Common Stock Issued and Outstanding (Details) - shares			2 Months Ended	3 Months Ended	9 Months Ended
	Nov. 22, 2023	Nov. 10, 2023	Dec. 05, 2023	Sep. 30, 2022	Sep. 30, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)			103,704,006	103,039,304	102,563,042
Common shares outstanding - beginning of period (in shares)			103,704,006	103,039,304	102,563,042
Share class conversions (in shares)				0	0
Common shares issued - end of period (in shares)				103,087,859	103,087,859
Common shares outstanding - end of period (in shares)				103,087,859	103,087,859
Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
IPO shares issued (in shares)			6,250,000
Share class conversions (in shares)			0
Exercise of warrants (in shares)			271,097
Common shares issued - end of period (in shares)			110,225,103
Common shares outstanding - end of period (in shares)			110,225,103
Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)			30,520,078	30,520,078	30,320,078
Common shares outstanding - beginning of period (in shares)			30,520,078	30,520,078	30,320,078
Share class conversions (in shares)				0	200,000
Common shares issued - end of period (in shares)				30,520,078	30,520,078
Common shares outstanding - end of period (in shares)				30,520,078	30,520,078
Common Class A | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
IPO shares issued (in shares)			0
Share class conversions (in shares)			(1,875,271)
Exercise of warrants (in shares)			0
Common shares issued - end of period (in shares)			28,644,807
Common shares outstanding - end of period (in shares)			28,644,807
Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)			42,658,302	40,497,039	37,935,266
Common shares outstanding - beginning of period (in shares)			42,658,302	40,497,039	37,935,266
Share class conversions (in shares)				1,496,561	3,582,072
Common shares issued - end of period (in shares)				42,042,155	42,042,155
Common shares outstanding - end of period (in shares)				42,042,155	42,042,155
Common Class B | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
IPO shares issued (in shares)			6,250,000
Share class conversions (in shares)	1,145,654	5,711,014	6,856,668
Exercise of warrants (in shares)			271,097
Common shares issued - end of period (in shares)			56,036,067
Common shares outstanding - end of period (in shares)			56,036,067
Common Class C
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued - beginning of period (in shares)			30,525,626	32,022,187	34,307,698
Common shares outstanding - beginning of period (in shares)			30,525,626	32,022,187	34,307,698
Share class conversions (in shares)				(1,496,561)	(3,782,072)
Common shares issued - end of period (in shares)				30,525,626	30,525,626
Common shares outstanding - end of period (in shares)				30,525,626	30,525,626
Common Class C | Subsequent Event
Increase (Decrease) in Stockholders' Equity [Roll Forward]
IPO shares issued (in shares)			0
Share class conversions (in shares)			(4,981,397)
Exercise of warrants (in shares)			0
Common shares issued - end of period (in shares)			25,544,229
Common shares outstanding - end of period (in shares)			25,544,229