Selective Insurance (SIGI) 10-Q 2 May 24 2024 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2024	Apr. 30, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-33067
Entity Registrant Name	SELECTIVE INSURANCE GROUP, INC
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	22-2168890
Entity Address, Address Line One	40 Wantage Avenue
Entity Address, City or Town	Branchville
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07890
City Area Code	(973)
Local Phone Number	948-3000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		60,792,024
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Entity Central Index Key	0000230557
Current Fiscal Year End Date	--12-31
Common stock:
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $2 per share
Trading Symbol	SIGI
Security Exchange Name	NASDAQ
Depositary Shares, each representing a 1/1,000th interest in a share of 4.60% Non-Cumulative Preferred Stock, Series B, without par value
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing a 1/1,000th interest in a share of 4.60% Non-Cumulative Preferred Stock, Series B, without par value
Trading Symbol	SIGIP
Security Exchange Name	NASDAQ

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investments:
Fixed income securities, held-to-maturity – at carrying value (fair value: $19,183 – 2024; $21,923 – 2023)	$ 20,295	$ 22,700
Less: allowance for credit losses	0	0
Fixed income securities, held-to-maturity, net of allowance for credit losses	20,295	22,700
Fixed income securities, available-for-sale – at fair value (allowance for credit losses: $30,381 – 2024 and $28,212 – 2023; amortized cost: $7,983,271 – 2024 and $7,880,697 – 2023)	7,583,504	7,499,197
Commercial mortgage loans – at carrying value (fair value: $197,807 – 2024 and $178,913 – 2023)	208,152	188,708
Less: allowance for credit losses	(122)	(291)
Commercial mortgage loans, net of allowance for credit losses	208,030	188,417
Equity securities – at fair value (cost:  $189,549 – 2024; $183,076 – 2023)	194,320	187,155
Short-term investments	247,883	309,317
Alternative investments	402,689	395,779
Other investments	88,960	91,164
Total investments (Note 4 and 5)	8,745,681	8,693,729
Cash	124	180
Restricted cash	11,720	13,092
Accrued investment income	68,034	66,339
Premiums receivable	1,459,112	1,331,979
Less: allowance for credit losses (Note 6)	(20,000)	(18,900)
Premiums receivable, net of allowance for credit losses	1,439,112	1,313,079
Reinsurance recoverable	653,085	658,525
Less: allowance for credit losses (Note 7)	(1,700)	(1,700)
Reinsurance recoverable, net of allowance for credit losses	651,385	656,825
Prepaid reinsurance premiums	207,979	203,320
Deferred federal income tax	144,719	140,237
Property and equipment – at cost, net of accumulated depreciation and amortization of: $277,945 – 2024; $271,409 – 2023	82,703	83,272
Deferred policy acquisition costs	448,340	424,864
Goodwill	7,849	7,849
Other assets	248,469	199,760
Total assets	12,056,115	11,802,546
Liabilities:
Reserve for loss and loss expense (Note 8)	5,501,750	5,336,911
Unearned premiums	2,440,992	2,330,656
Long-term debt	503,305	503,946
Current federal income tax	26,530	6,251
Accrued salaries and benefits	97,918	122,003
Other liabilities	479,126	548,398
Total liabilities	9,049,621	8,848,165
Stockholders’ Equity:
Preferred stock of $0 par value per share: Authorized shares 5,000,000; Issued shares: 8,000 with $25,000 liquidation preference per share - 2024 and 2023	200,000	200,000
Common stock of $2 par value per share: Authorized shares 360,000,000; Issued: 105,447,377 - 2024; 105,223,307 - 2023	210,895	210,447
Additional paid-in capital	534,327	522,748
Retained earnings	3,088,150	3,029,396
Accumulated other comprehensive income (loss) (Note 11)	(384,972)	(373,001)
Treasury stock – at cost (shares:  44,655,938 – 2024; 44,586,870 – 2023)	(641,906)	(635,209)
Total stockholders’ equity	3,006,494	2,954,381
Commitments and contingencies
Total liabilities and stockholders’ equity	$ 12,056,115	$ 11,802,546

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues:
Net premiums earned	$ 1,050,944	$ 902,336
Net investment income earned	107,849	91,506
Net realized and unrealized investment gains (losses)	(1,635)	3,344
Other income	7,801	2,634
Total revenues	1,164,959	999,820
Expenses:
Loss and loss expense incurred	704,292	567,438
Amortization of deferred policy acquisition costs	219,435	189,761
Other insurance expenses	115,987	108,588
Interest expense	7,181	7,166
Corporate expenses	15,498	12,108
Total expenses	1,062,393	885,061
Income before federal income tax	102,566	114,759
Federal income tax expense:
Current	21,413	25,505
Deferred	(1,365)	(3,320)
Total federal income tax expense	20,048	22,185
Net income	82,518	92,574
Preferred stock dividends	2,300	2,300
Net income available to common stockholders, basic	80,218	90,274
Net income available to common stockholders, diluted	$ 80,218	$ 90,274
Earnings per common share:
Net income available to common stockholders - Basic (in dollars per share)	$ 1.32	$ 1.49
Net income available to common stockholders - DIluted (in dollars per share)	$ 1.31	$ 1.48

Unaudited Consolidated Statem_2

Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 82,518	$ 92,574
Other comprehensive income (loss), net of tax:
Unrealized holding gains (losses) arising during period	(12,293)	52,079
Unrealized gains (losses) on securities with credit loss recognized in earnings	(2,474)	17,721
Net realized (gains) losses on disposals and losses on intent-to-sell available-for-sale securities	(61)	4,822
Credit loss (benefit) expense	2,093	(7,527)
Total unrealized gains (losses) on investment securities	(12,735)	67,095
Net actuarial loss	764	598
Total defined benefit pension and post-retirement plans	764	598
Other comprehensive income (loss)	(11,971)	67,693
Comprehensive income (loss)	$ 70,547	$ 160,267

Unaudited Consolidated Statem_3

Unaudited Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred stock:	Common stock:	Additional paid-in capital:	Retained earnings:	Accumulated other comprehensive income (loss):	Treasury stock:
Beginning of period at Dec. 31, 2022		$ 200,000	$ 209,694	$ 493,488	$ 2,749,703	$ (498,042)	$ (627,279)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock		0
Dividend reinvestment plan			9	459
Stock purchase and compensation plans			446	8,766
Net income	$ 92,574				92,574
Dividends to preferred stockholders					(2,300)
Dividends to common stockholders					(18,364)
Other comprehensive income (loss)	67,693					67,693
Acquisition of treasury stock - shares acquired related to employee share-based compensation plans							(7,443)
End of period at Mar. 31, 2023	$ 2,669,404	$ 200,000	210,149	502,713	2,821,613	(430,349)	(634,722)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per preferred share (in dollars per share)	$ 287.50
Dividends declared per common share (in dollars per share)	$ 0.30
Preferred stock, shares outstanding, beginning balance (in shares) at Dec. 31, 2022	8,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock (in shares)		0
Preferred stock, shares outstanding, ending balance (in shares) at Mar. 31, 2023	8,000
Common stock, shares outstanding, beginning of period (in shares) at Dec. 31, 2022	60,338,900
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend reinvestment plan (in shares)	4,650
Stock purchase and compensation plan (in shares)	222,816
Acquisition of treasury stock - shares acquired related to employee share-based compensation plans (in shares)	(73,780)
Common stock, shares outstanding, end of period (in shares) at Mar. 31, 2023	60,492,586
Beginning of period at Dec. 31, 2023	$ 2,954,381	$ 200,000	210,447	522,748	3,029,396	(373,001)	(635,209)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock		0
Dividend reinvestment plan			10	488
Stock purchase and compensation plans			438	11,091
Net income	82,518				82,518
Dividends to preferred stockholders					(2,300)
Dividends to common stockholders					(21,464)
Other comprehensive income (loss)	(11,971)					(11,971)
Acquisition of treasury stock - shares acquired related to employee share-based compensation plans							(6,697)
End of period at Mar. 31, 2024	$ 3,006,494	$ 200,000	$ 210,895	$ 534,327	$ 3,088,150	$ (384,972)	$ (641,906)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per preferred share (in dollars per share)	$ 287.50
Dividends declared per common share (in dollars per share)	$ 0.35
Preferred stock, shares outstanding, beginning balance (in shares) at Dec. 31, 2023	8,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock (in shares)		0
Preferred stock, shares outstanding, ending balance (in shares) at Mar. 31, 2024	8,000
Common stock, shares outstanding, beginning of period (in shares) at Dec. 31, 2023	60,636,437
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend reinvestment plan (in shares)	4,806
Stock purchase and compensation plan (in shares)	219,264
Acquisition of treasury stock - shares acquired related to employee share-based compensation plans (in shares)	(69,068)
Common stock, shares outstanding, end of period (in shares) at Mar. 31, 2024	60,791,439

Unaudited Consolidated Statem_4

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Activities
Net income	$ 82,518	$ 92,574
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	9,084	8,957
Stock-based compensation expense	10,115	7,719
Undistributed gains of equity method investments	(5,873)	(6,693)
Distributions in excess of current year income of equity method investments	5,148	1,876
Net realized and unrealized (gains) losses	1,635	(3,344)
Changes in assets and liabilities:
Increase in reserve for loss and loss expense, net of reinsurance recoverable	170,279	70,397
Increase in unearned premiums, net of prepaid reinsurance	105,677	97,432
Decrease in net federal income taxes	18,979	20,522
Increase in premiums receivable	(126,033)	(68,478)
Increase in deferred policy acquisition costs	(23,476)	(19,320)
(Increase) decrease in accrued investment income	(2,091)	1,456
Decrease in accrued salaries and benefits	(24,085)	(26,406)
Increase in other assets	(6,226)	(4,083)
Decrease in other liabilities	(101,445)	(36,840)
Net cash provided by (used in) operating activities	114,206	135,769
Investing Activities
Purchases of fixed income securities, available-for-sale	(521,745)	(1,003,617)
Purchases of commercial mortgage loans	(22,256)	(8,447)
Purchases of equity securities	(6,473)	(3,229)
Purchases of alternative investments and other investments	(12,738)	(7,736)
Purchases of short-term investments	(1,232,780)	(1,361,774)
Sales of fixed income securities, available-for-sale	219,889	639,365
Proceeds from commercial mortgage loans	2,812	469
Sales of short-term investments	1,294,522	1,499,963
Redemption and maturities of fixed income securities, held-to-maturity	2,404	6,507
Redemption and maturities of fixed income securities, available-for-sale	193,109	109,999
Sales of equity securities	0	32,918
Distributions from alternative investments and other investments	3,448	2,854
Purchases of property and equipment	(6,199)	(5,510)
Net cash provided by (used in) investing activities	(86,007)	(98,238)
Financing Activities
Dividends to preferred stockholders	(2,300)	(2,300)
Dividends to common stockholders	(20,784)	(17,690)
Acquisition of treasury stock	(6,697)	(7,443)
Net proceeds from stock purchase and compensation plans	885	973
Repayments of finance lease obligations	(731)	(615)
Net cash provided by (used in) financing activities	(29,627)	(27,075)
Net increase (decrease) in cash and restricted cash	(1,428)	10,456
Cash and restricted cash, beginning of period	13,272	25,209
Cash and restricted cash, end of period	$ 11,844	$ 35,665

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Fixed income securities, held-to-maturity, fair value	$ 19,183	$ 21,923
Fixed income securities, available-for-sale, allowance for credit loss	30,381	28,212
Fixed income securities, available-for-sale, amortized cost	7,983,271	7,880,697
Commercial mortgage loans, fair value	197,807	178,913
Equity securities, cost	189,549	183,076
Property and equipment, accumulated depreciation and amortization	$ 277,945	$ 271,409
Preferred stock, par or stated value (in dollars per share)	$ 0	$ 0
Preferred stock, authorized (in shares)	5,000,000	5,000,000
Preferred stock, issued (in shares)	8,000	8,000
Preferred stock, liquidation preference (in dollars per share)	$ 25,000	$ 25,000
Common stock, par or stated value (in dollars per share)	$ 2	$ 2
Common stock, authorized (in shares)	360,000,000	360,000,000
Common stock, issued (in shares)	105,447,377	105,223,307
Treasury stock, common (in shares)	44,655,938	44,586,870

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The words "Company,” “we,” “us,” or “our” refer to Selective Insurance Group, Inc. (the "Parent") and its subsidiaries, except as expressly indicated or the context requires otherwise. We have prepared our interim unaudited consolidated financial statements (“Financial Statements”) in conformity with (i) United States ("U.S.") generally accepted accounting principles (“GAAP”), and (ii) the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. These require management to make estimates and assumptions that affect the reported financial statement balances and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates. All significant intercompany accounts and transactions are eliminated in consolidation.

Adoption of Accounting Pronounc

Adoption of Accounting Pronouncements	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Adoption of Accounting Pronouncements	Adoption of Accounting Pronouncements In June 2022, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2022-03, Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions (“ASU 2022-03”). ASU 2022-03 clarifies that a contractual sales restriction on an equity security is not considered when determining the security's fair value. This ASU was issued to eliminate diversity in practice by clarifying that contractual arrangements restricting an entity's ability to sell the security for a certain period of time is a characteristic of the reporting entity and should not be contemplated when determining the security's fair value. ASU 2022-03 requires new disclosures that provide investors with information about the restriction, including the nature and remaining duration of the restriction. The ASU is effective for annual periods beginning after December 15, 2023, including interim periods within those annual periods. We adopted this guidance on January 1, 2024 and it did not have a material impact to our financial condition, results of operations, or disclosures. In March 2023, the FASB issued ASU 2023-02, Investments — Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method ("ASU 2023-02"). This ASU allows companies to elect to account for qualifying tax equity investments, regardless of the tax credit program from which the income tax credits are received, using the proportional amortization method if certain conditions are met. Companies were previously permitted to apply the proportional amortization method only to qualifying tax equity investments in low income housing tax credit structures. ASU 2023-02 extends the application of the proportional amortization method to qualifying tax equity investments that generate tax credits through other programs. It also requires new disclosures that provide a better understanding of the nature of the tax equity investments and the effect the tax equity investments and related income tax credits and other income tax benefits have on a company's financial position and results of operations. The ASU is effective for annual periods beginning after December 15, 2023, including interim periods within those fiscal years. We adopted ASU 2023-02 on January 1, 2024 and it did not have a material impact to our financial condition, results of operations, or disclosures. Pronouncements to be effective in the future In November 2023, the FASB issued ASU 2023-07, Improvements to Reportable Segment Disclosures ("ASU 2023-07"). ASU 2023-07 amends disclosure requirements for segment reporting by modifying and adding disclosure requirements. The additional disclosure requirements include the following on both an interim and annual basis: (i) significant segment expenses that are regularly provided to the chief operating decision maker ("CODM"); (ii) amounts for "other segment items" by reportable segment and a description of its composition; and (iii) the title and position of the CODM and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. In addition, ASU 2023-07 requires all annual disclosures about a reportable segment’s profit or loss and assets currently required by Topic 280, Segment Reporting , to now be disclosed in interim periods. ASU 2023-07 is effective for annual periods beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. As it only requires additional disclosure, ASU 2023-07 will not have an impact on our financial condition or results of operations. In December 2023, the FASB issued ASU 2023-09, Improvements to Income Tax Disclosures (“ASU 2023-09”). ASU 2023-09 amends disclosure requirements to provide greater transparency on income taxes. The following additional disclosures are required annually: (i) specific required categories in the rate reconciliation, (ii) additional information for reconciling items that meet a quantitative threshold, (iii) the amount of income taxes paid disaggregated by jurisdiction, and (iv) income tax expense (or benefit) from continuing operations disaggregated by federal, state, and foreign. ASU 2023-09 is effective for annual periods beginning after December 15, 2024. Amendments can be applied on a prospective basis; however, retrospective application is permitted. Early adoption is permitted. As it only requires additional disclosure, ASU 2023-09 will not have an impact on our financial condition or results of operations.

Statements of Cash Flows

Statements of Cash Flows	3 Months Ended
	Mar. 31, 2024
Supplemental Cash Flow Information [Abstract]
Statements of Cash Flows	Statements of Cash Flows Supplemental cash flow information was as follows: Quarter ended March 31, ($ in thousands) 2024 2023 Cash paid (received) during the period for: Interest $ 8,544 8,528 Federal income tax — — Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases 1,777 2,235 Operating cash flows from financing leases 22 11 Financing cash flows from finance leases 731 615 Non-cash items: Corporate actions related to fixed income securities, available-for-sale ("AFS") 1 2,298 4,629 Assets acquired under finance lease arrangements 3 — Assets acquired under operating lease arrangements 674 4,237 Non-cash purchase of property and equipment 8 23 1 Examples of corporate actions include like-kind exchanges, non-cash acquisitions, and stock splits. The following table provides a reconciliation of cash and restricted cash reported within the Consolidated Balance Sheets that equate to the amount reported in the Consolidated Statements of Cash Flows: ($ in thousands) March 31, 2024 December 31, 2023 Cash $ 124 180 Restricted cash 11,720 13,092 Total cash and restricted cash shown in the Consolidated Statements of Cash Flows $ 11,844 13,272 Amounts in restricted cash represent cash received from the National Flood Insurance Program ("NFIP") that can only be used to pay flood claims under the Write Your Own program.

Investments

Investments	3 Months Ended
	Mar. 31, 2024
Investments [Abstract]
Investments	Investments (a) Information regarding our AFS securities as of March 31, 2024 and December 31, 2023, were as follows: March 31, 2024 Cost/ Allowance for Credit Losses Unrealized Unrealized Fair ($ in thousands) AFS fixed income securities: U.S. government and government agencies $ 161,335 — 70 (19,579) 141,826 Foreign government 10,703 (29) — (1,445) 9,229 Obligations of states and political subdivisions 570,438 (695) 1,101 (31,858) 538,986 Corporate securities 2,930,310 (15,442) 20,367 (140,185) 2,795,050 Collateralized loan obligations ("CLO") and other asset-backed securities ("ABS") 1,958,551 (2,627) 15,158 (73,997) 1,897,085 Residential mortgage-backed securities ("RMBS") 1,623,948 (11,580) 3,828 (104,237) 1,511,959 Commercial mortgage-backed securities ("CMBS") 727,986 (8) 1,103 (39,712) 689,369 Total AFS fixed income securities $ 7,983,271 (30,381) 41,627 (411,013) 7,583,504 December 31, 2023 Cost/ Allowance for Credit Losses Unrealized Unrealized Fair ($ in thousands) AFS fixed income securities: U.S. government and government agencies $ 223,157 — 139 (18,261) 205,035 Foreign government 11,140 (35) — (1,302) 9,803 Obligations of states and political subdivisions 612,938 (669) 2,623 (28,927) 585,965 Corporate securities 2,834,048 (12,999) 28,078 (137,888) 2,711,239 CLO and other ABS 1,911,831 (2,854) 11,855 (86,005) 1,834,827 RMBS 1,568,960 (11,649) 6,023 (85,851) 1,477,483 CMBS 718,623 (6) 1,358 (45,130) 674,845 Total AFS fixed income securities $ 7,880,697 (28,212) 50,076 (403,364) 7,499,197 The following tables provide a roll forward of the allowance for credit losses on our AFS fixed income securities for the indicated periods: Quarter ended March 31, 2024 Beginning Balance Current Provision for Securities without Prior Allowance Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance ($ in thousands) Foreign government $ 35 — — — (6) — 29 Obligations of states and political subdivisions 669 9 — 25 (8) — 695 Corporate securities 12,999 1,015 — 1,792 (355) (9) 15,442 CLO and other ABS 2,854 90 — (314) (3) — 2,627 RMBS 11,649 — — 31 (100) — 11,580 CMBS 6 2 — — — — 8 Total AFS fixed income securities $ 28,212 1,116 — 1,534 (472) (9) 30,381 Quarter ended March 31, 2023 Beginning Balance Current Provision for Securities without Prior Allowance Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance ($ in thousands) Foreign government $ 284 — — (248) — — 36 Obligations of states and political subdivisions 1,024 50 — (254) (83) — 737 Corporate securities 30,330 2,854 — (13,964) (2,453) (11) 16,756 CLO and other ABS 2,375 787 — 736 (3) — 3,895 RMBS 11,597 12 — 219 (88) — 11,740 CMBS 111 27 — 252 — — 390 Total AFS fixed income securities $ 45,721 3,730 — (13,259) (2,627) (11) 33,554 During First Quarter 2024 and First Quarter 2023, we had no write-offs or recoveries of our AFS fixed income securities. For information on our methodology and significant inputs used to measure expected credit losses, our accounting policy for recognizing write-offs of uncollectible amounts, and our treatment of accrued interest, refer to Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2023 Annual Report. Accrued interest on AFS securities was $66.3 million as of March 31, 2024, and $64.6 million as of December 31, 2023. We did not record any write-offs of accrued interest in First Quarter 2024 and First Quarter 2023. (b) Quantitative information about unrealized losses on our AFS portfolio follows: March 31, 2024 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: U.S. government and government agencies $ 8,149 (49) 107,151 (19,530) 115,300 (19,579) Foreign government — — 9,229 (1,445) 9,229 (1,445) Obligations of states and political subdivisions 161,084 (1,289) 303,259 (30,569) 464,343 (31,858) Corporate securities 316,330 (4,043) 1,446,157 (136,142) 1,762,487 (140,185) CLO and other ABS 385,471 (7,527) 824,843 (66,470) 1,210,314 (73,997) RMBS 511,009 (8,770) 761,356 (95,467) 1,272,365 (104,237) CMBS 133,266 (2,033) 494,395 (37,679) 627,661 (39,712) Total AFS fixed income securities $ 1,515,309 (23,711) 3,946,390 (387,302) 5,461,699 (411,013) December 31, 2023 Less than 12 months 12 months or longer Total ($ in thousands) Fair Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: U.S. government and government agencies $ 77,698 (188) 108,578 (18,073) 186,276 (18,261) Foreign government 1,552 (87) 8,251 (1,215) 9,803 (1,302) Obligations of states and political subdivisions 137,031 (962) 290,964 (27,965) 427,995 (28,927) Corporate securities 263,423 (6,369) 1,439,422 (131,519) 1,702,845 (137,888) CLO and other ABS 278,940 (7,120) 984,175 (78,885) 1,263,115 (86,005) RMBS 351,976 (4,765) 757,914 (81,086) 1,109,890 (85,851) CMBS 130,189 (2,995) 471,256 (42,135) 601,445 (45,130) Total AFS fixed income securities $ 1,240,809 (22,486) 4,060,560 (380,878) 5,301,369 (403,364) We currently do not intend to sell any of the securities summarized in the tables above, nor do we believe we will be required to sell any of them. Considering these factors and our review of these securities under our credit loss policy as described in Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2023 Annual Report, we have concluded that no additional allowance for credit loss is required on these balances beyond the allowance for credit loss recorded as of March 31, 2024. This conclusion reflects our current judgment about the financial position and future prospects of the entities that issued the investment security and underlying collateral. (c) AFS and held-to-maturity ("HTM") fixed income securities at March 31, 2024, by contractual maturity are shown below. The maturities of RMBS, CMBS, CLO and other ABS securities were calculated using each security's estimated average life. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. AFS HTM ($ in thousands) Fair Value Carrying Value Fair Value Due in one year or less $ 582,163 — — Due after one year through five years 3,435,983 15,716 14,898 Due after five years through 10 years 2,833,659 4,579 4,285 Due after 10 years 731,699 — — Total fixed income securities $ 7,583,504 20,295 19,183 (d) The following table summarizes our alternative investment portfolio by strategy: March 31, 2024 December 31, 2023 ($ in thousands) Carrying Value Remaining Commitment Maximum Exposure to Loss Carrying Value Remaining Commitment Maximum Exposure to Loss Alternative Investments Private equity $ 306,444 137,986 444,430 301,759 131,885 433,644 Private credit 53,392 90,569 143,961 54,500 89,401 143,901 Real assets 42,853 31,100 73,953 39,520 33,040 72,560 Total alternative investments $ 402,689 259,655 662,344 395,779 254,326 650,105 We are contractually committed to make additional investments up to the remaining commitments stated above. We did not provide any non-contractual financial support during 2024 or 2023. The following table shows gross summarized financial information for our alternative investments portfolio, including the portion we do not own. As the majority of these investments report results to us on a one quarter lag, the summarized financial statement information is for the three-month period ended December 31: Income Statement Information Quarter ended March 31, ($ in millions) 2024 2023 Net investment income (loss) $ (346.0) (70.7) Realized gains 1,830.8 1,722.3 Net change in unrealized appreciation (depreciation) 3,819.0 1,443.7 Net income $ 5,303.8 3,095.3 Alternative investment income included in "Net investment income earned" on our Consolidated Statements of Income $ 6.9 7.8 (e) We have pledged certain AFS fixed income securities as collateral related to our borrowing relationships with the Federal Home Loan Bank of Indianapolis ("FHLBI") and the Federal Home Loan Bank of New York ("FHLBNY"). In addition, we had certain securities on deposit with various state and regulatory agencies at March 31, 2024 to comply with insurance laws. We retain all rights regarding all securities pledged as collateral. The following table summarizes the market value of these securities at March 31, 2024: ($ in millions) FHLBI Collateral FHLBNY Collateral State and Total U.S. government and government agencies $ — — 20.0 20.0 Obligations of states and political subdivisions — — 4.2 4.2 RMBS 66.2 24.1 — 90.3 CMBS 2.3 8.5 — 10.8 Total pledged as collateral $ 68.5 32.6 24.2 125.3 (f) We did not have exposure to any credit concentration risk of a single issuer greater than 10% of our stockholders' equity, other than to certain U.S. government agencies, as of March 31, 2024, or December 31, 2023. (g) The components of pre-tax net investment income earned were as follows: Quarter ended March 31, ($ in thousands) 2024 2023 Fixed income securities $ 94,102 80,087 Commercial mortgage loans ("CMLs") 2,794 1,965 Equity securities 4,908 1,205 Short-term investments 3,519 4,650 Alternative investments 6,881 7,768 Other investments 263 43 Investment expenses (4,618) (4,212) Net investment income earned $ 107,849 91,506 (h) The following table summarizes net realized and unrealized investment gains and losses for the periods indicated: Quarter ended March 31, ($ in thousands) 2024 2023 Gross gains on sales $ 2,135 3,784 Gross losses on sales (1,965) (12,930) Net realized gains (losses) on disposals 170 (9,146) Net unrealized gains (losses) on equity securities 692 3,248 Net credit loss benefit (expense) on fixed income securities, AFS (2,650) 9,529 Net credit loss benefit (expense) on CMLs 168 17 Losses on securities for which we have the intent to sell (15) (304) Net realized and unrealized investment gains (losses) $ (1,635) 3,344 Net unrealized gains and losses recognized in income on equity securities, as reflected in the table above, included the following: Quarter ended March 31, ($ in thousands) 2024 2023 Unrealized gains (losses) recognized in income on equity securities: On securities remaining in our portfolio at end of period $ 692 (142) On securities sold in period — 3,390 Total unrealized gains (losses) recognized in income on equity securities $ 692 3,248

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The financial assets in our investment portfolio are primarily measured at fair value as disclosed on the Consolidated Balance Sheets. The following table presents the carrying amounts and fair values of our financial liabilities as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 ($ in thousands) Carrying Amount Fair Value Carrying Amount Fair Value Financial Liabilities Long-term debt: 7.25% Senior Notes $ 49,927 51,137 49,926 53,047 6.70% Senior Notes 99,571 101,666 99,565 104,039 5.375% Senior Notes 294,548 286,927 294,523 288,787 3.03% borrowings from FHLBI 60,000 57,568 60,000 57,932 Subtotal long-term debt 504,046 497,298 504,014 503,805 Unamortized debt issuance costs (2,650) (2,704) Finance lease obligations 1,909 2,636 Total long-term debt $ 503,305 503,946 For discussion regarding the fair value techniques of our financial instruments, refer to Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2023 Annual Report. The following tables provide quantitative disclosures of our financial assets that were measured and recorded at fair value at March 31, 2024, and December 31, 2023: March 31, 2024 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in Significant Other Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 141,826 33,530 108,296 — Foreign government 9,229 — 9,229 — Obligations of states and political subdivisions 538,986 — 531,239 7,747 Corporate securities 2,795,050 — 2,507,554 287,496 CLO and other ABS 1,897,085 — 1,636,988 260,097 RMBS 1,511,959 — 1,511,959 — CMBS 689,369 — 689,014 355 Total AFS fixed income securities 7,583,504 33,530 6,994,279 555,695 Equity securities: Common stock 1 192,510 36,333 — 1,067 Preferred stock 1,810 1,810 — — Total equity securities 194,320 38,143 — 1,067 Short-term investments 247,883 246,904 979 — Total assets measured at fair value $ 8,025,707 318,577 6,995,258 556,762 December 31, 2023 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in Significant Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 205,035 34,056 170,979 — Foreign government 9,803 — 9,803 — Obligations of states and political subdivisions 585,965 — 578,131 7,834 Corporate securities 2,711,239 — 2,413,907 297,332 CLO and other ABS 1,834,827 — 1,589,514 245,313 RMBS 1,477,483 — 1,477,483 — CMBS 674,845 — 674,489 356 Total AFS fixed income securities 7,499,197 34,056 6,914,306 550,835 Equity securities: Common stock 1 185,339 20,582 — 854 Preferred stock 1,816 1,816 — — Total equity securities 187,155 22,398 — 854 Short-term investments 309,317 308,512 805 — Total assets measured at fair value $ 7,995,669 364,966 6,915,111 551,689 1 Investments amounting to $155.1 million at March 31, 2024, and $163.9 million at December 31, 2023, were measured at fair value using the net asset value per share (or its practical expedient) and have not been classified in the fair value hierarchy. These investments are not redeemable and the timing of liquidations of the underlying assets is unknown at each reporting period. The fair value amounts in this table are intended to permit reconciliation of the fair value hierarchy to total assets measured at fair value. The following tables provide a summary of Level 3 changes in First Quarter 2024 and First Quarter 2023: March 31, 2024 ($ in thousands) Obligations of States and Political Subdivisions Corporate Securities CLO and Other ABS CMBS Common Stock Total Fair value, December 31, 2023 $ 7,834 297,332 245,313 356 854 551,689 Total net gains (losses) for the period included in: Other comprehensive income (loss) ("OCI") (86) (376) 399 3 — (60) Net realized and unrealized gains (losses) (1) 140 57 — 213 409 Net investment income earned — 280 (1) (1) — 278 Purchases — 1,152 14,658 — — 15,810 Sales — — — — — — Issuances — — — — — — Settlements — (2,870) (1,173) (3) — (4,046) Transfers into Level 3 — 20,065 19,537 — — 39,602 Transfers out of Level 3 — (28,227) (18,693) — — (46,920) Fair value, March 31, 2024 $ 7,747 287,496 260,097 355 1,067 556,762 Change in unrealized gains (losses) for the period included in earnings for assets held at period end (1) 140 57 — 213 409 Change in unrealized gains (losses) for the period included in OCI for assets held at period end (86) (376) 399 3 — (60) March 31, 2023 ($ in thousands) Obligation of state and Political Subdivisions Corporate Securities CLO and Other ABS CMBS Common Stock Total Fair value, December 31, 2022 $ 6,661 187,980 153,342 375 897 349,255 Total net gains (losses) for the period included in: OCI 152 2,405 696 17 — 3,270 Net realized and unrealized gains (losses) 61 72 (73) — (269) (209) Net investment income earned — 12 (32) (1) — (21) Purchases — 24,799 13,403 — — 38,202 Sales — — — — — — Issuances — — — — — — Settlements — (4,044) (1,192) (3) — (5,239) Transfers into Level 3 — 361 14,148 2,848 — 17,357 Transfers out of Level 3 — — (534) — — (534) Fair value, March 31, 2023 $ 6,874 211,585 179,758 3,236 628 402,081 Change in unrealized gains (losses) for the period included in earnings for assets held at period end 61 72 (73) — (269) (209) Change in unrealized gains (losses) for the period included in OCI for assets held at period end 152 2,405 696 17 — 3,270 The following tables present quantitative information about the significant unobservable inputs used in the fair value measurements of Level 3 assets at March 31, 2024, and December 31, 2023: March 31, 2024 ($ in thousands) Assets Measured at Fair Value Valuation Techniques Unobservable Inputs Range Weighted Average Internal valuations: Corporate securities $ 155,633 Discounted Cash Flow Illiquidity Spread (4.4)% - 5.3% 1.8% CLO and other ABS 155,287 Discounted Cash Flow Illiquidity Spread 0.01% - 19.6% 2.4% Total internal valuations 310,920 Other 1 245,842 Total Level 3 securities $ 556,762 December 31, 2023 ($ in thousands) Assets Measured at Fair Value Valuation Techniques Unobservable Inputs Range Weighted Average Internal valuations: Corporate securities $ 135,524 Discounted Cash Flow Illiquidity Spread (4.4)% - 5.3% 1.9% CLO and other ABS 127,210 Discounted Cash Flow Illiquidity Spread 0.01% - 19.6% 2.4% Total internal valuations 262,734 Other 1 288,955 Total Level 3 securities $ 551,689 1 Other is comprised of broker quotes or other third-party pricing for which there is a lack of transparency into the inputs used to develop the valuations. The quantitative details of these unobservable inputs are neither provided to us, nor reasonably available to us, and therefore are not included in the tables above. For the securities in the tables above valued using a discounted cash flow analysis, we apply an illiquidity spread in our determination of fair value. An increase in this assumption would result in a lower fair value measurement. The following tables provide quantitative information about our financial assets and liabilities that were not measured at fair value, but were disclosed as such at March 31, 2024, and December 31, 2023: March 31, 2024 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Corporate securities $ 19,183 — 19,183 — Total HTM fixed income securities 19,183 — 19,183 — CMLs $ 197,807 — — 197,807 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 51,137 — 51,137 — 6.70% Senior Notes 101,666 — 101,666 — 5.375% Senior Notes 286,927 — 286,927 — 3.03% borrowings from FHLBI 57,568 — 57,568 — Total long-term debt $ 497,298 — 497,298 — December 31, 2023 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Corporate securities 21,923 — 21,923 — Total HTM fixed income securities $ 21,923 — 21,923 — CMLs $ 178,913 — — 178,913 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 53,047 — 53,047 — 6.70% Senior Notes 104,039 — 104,039 — 5.375% Senior Notes 288,787 — 288,787 — 3.03% borrowings from FHLBI 57,932 — 57,932 — Total long-term debt $ 503,805 — 503,805 —

Allowance for Credit Losses on

Allowance for Credit Losses on Premiums Receivable	3 Months Ended
	Mar. 31, 2024
Premiums Receivable Disclosure [Abstract]
Allowance for Credit Losses on Premiums Receivable	Allowance for Credit Losses on Premiums Receivable The following table provides a roll forward of the allowance for credit losses on our premiums receivable balance for the indicated periods: Quarter ended March 31, ($ in thousands) 2024 2023 Balance at beginning of period $ 18,900 16,100 Current period change for expected credit losses 1,784 1,910 Write-offs charged against the allowance for credit losses (1,056) (1,164) Recoveries 372 254 Allowance for credit losses, end of period $ 20,000 17,100 For a discussion of the methodology used to evaluate our estimate of expected credit losses on premiums receivable, refer to Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2023 Annual Report.

Reinsurance

Reinsurance	3 Months Ended
	Mar. 31, 2024
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance We evaluate and monitor the financial condition of our reinsurers under voluntary reinsurance arrangements to minimize our exposure to significant losses from reinsurer insolvencies. The following tables provide (i) a disaggregation of our reinsurance recoverable balance by financial strength rating, and (ii) an aging analysis of our past due reinsurance recoverable balances as of March 31, 2024, and December 31, 2023: March 31, 2024 ($ in thousands) Current Past Due Total Reinsurance Recoverables Financial strength rating of rated reinsurers A++ $ 83,372 53 83,425 A+ 366,428 1,172 367,600 A 115,086 582 115,668 A- 3,865 89 3,954 Total rated reinsurers 568,751 1,896 570,647 Non-rated reinsurers Federal and state pools 77,799 — 77,799 Other than federal and state pools 4,135 504 4,639 Total non-rated reinsurers 81,934 504 82,438 Total reinsurance recoverable, gross $ 650,685 2,400 653,085 Less: allowance for credit losses (1,700) Total reinsurance recoverable, net 651,385 December 31, 2023 ($ in thousands) Current Past Due Total Reinsurance Recoverables Financial strength rating of rated reinsurers A++ $ 82,466 21 82,487 A+ 371,132 2,887 374,019 A 111,883 1,380 113,263 A- 3,596 89 3,685 Total rated reinsurers 569,077 4,377 573,454 Non-rated reinsurers Federal and state pools 80,506 — 80,506 Other than federal and state pools 4,488 77 4,565 Total non-rated reinsurers 84,994 77 85,071 Total reinsurance recoverable, gross $ 654,071 4,454 658,525 Less: allowance for credit losses (1,700) Total reinsurance recoverable, net 656,825 The following table provides a roll forward of the allowance for credit losses on our reinsurance recoverable balance for the periods indicated: Quarter ended March 31, ($ in thousands) 2024 2023 Balance at beginning of period $ 1,700 1,600 Current period change for expected credit losses — 700 Write-offs charged against the allowance for credit losses — — Recoveries — — Allowance for credit losses, end of period $ 1,700 2,300 For a discussion of the methodology used to evaluate our estimate of expected credit losses on our reinsurance recoverable balance, refer to Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2023 Annual Report. The following table lists direct, assumed, and ceded reinsurance amounts for premiums written, premiums earned, and loss and loss expense incurred for the indicated periods. For more information about reinsurance, refer to Note 9. “Reinsurance” in Item 8. “Financial Statements and Supplementary Data.” of our 2023 Annual Report. Quarter ended March 31, ($ in thousands) 2024 2023 Premiums written: Direct $ 1,315,911 1,132,760 Assumed 5,985 5,394 Ceded (165,275) (138,386) Net 1,156,621 999,768 Premiums earned: Direct 1,205,368 1,032,228 Assumed 6,191 6,290 Ceded (160,615) (136,182) Net 1,050,944 902,336 Loss and loss expense incurred: Direct 753,567 613,229 Assumed 5,981 5,255 Ceded (55,256) (51,046) Net $ 704,292 567,438

Reserve for Loss and Loss Expen

Reserve for Loss and Loss Expense	3 Months Ended
	Mar. 31, 2024
Insurance Loss Reserves [Abstract]
Reserve for Loss and Loss Expense	Reserve for Loss and Loss Expense The table below provides a roll forward of the reserve for loss and loss expense for beginning and ending reserve balances: Quarter ended March 31, ($ in thousands) 2024 2023 Gross reserve for loss and loss expense, at beginning of period $ 5,336,911 5,144,821 Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of period 618,601 757,513 Net reserve for loss and loss expense, at beginning of period 4,718,310 4,387,308 Incurred loss and loss expense for claims occurring in the: Current year 688,519 580,408 Prior years 15,773 (12,970) Total incurred loss and loss expense 704,292 567,438 Paid loss and loss expense for claims occurring in the: Current year 107,719 91,011 Prior years 435,489 418,194 Total paid loss and loss expense 543,208 509,205 Net reserve for loss and loss expense, at end of period 4,879,394 4,445,541 Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 622,356 653,909 Gross reserve for loss and loss expense, at end of period $ 5,501,750 5,099,450 Prior year reserve development in First Quarter 2024 was unfavorable by $15.8 million, consisting of $35.0 million of unfavorable casualty reserve development, partially offset by $19.2 million of favorable property reserve development. The unfavorable casualty reserve development was driven by our Standard Commercial Lines segment, which included (i) $50.0 million in our general liability line of business, primarily driven by increased severities in accident years 2020 through 2023, partially offset by (ii) $15.0 million of favorable casualty reserve development in our workers compensation line of business. Additionally, in our Standard Personal Lines segment, we had unfavorable casualty reserve development of $5.0 million in our personal automobile line of business, offset by favorable development of $5.0 million in our homeowners line of business. Prior year reserve development in First Quarter 2023 was favorable by $13.0 million, consisting of favorable casualty reserve development of $10.0 million in our workers compensation line of business and $5.0 million in our Excess and Surplus ("E&S") casualty lines of business, partially offset by $2.0 million of unfavorable casualty reserve development in our personal automobile line of business.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Segment Information	Segment Information We evaluate the results of our four reportable segments as follows: • Our Standard Commercial Lines, Standard Personal Lines, and E&S Lines are evaluated on (i) before and after-tax underwriting results (net premiums earned, incurred loss and loss expense, policyholder dividends, policy acquisition costs, and other underwriting expenses), (ii) their return on equity ("ROE") contribution, and (iii) their combined ratios. • Our Investments segment is primarily evaluated on after-tax net investment income and its ROE contribution. After-tax net realized and unrealized gains and losses are also included in our Investments segment results. In computing each segment's results, we do not make adjustments for interest expense or corporate expenses. No segment has a separate investment portfolio or allocated assets. The following summaries present revenues (net investment income and net realized and unrealized gains and losses on investments in the case of the Investments segment) and pre-tax income for the individual segments: Revenue by Segment Quarter ended March 31, ($ in thousands) 2024 2023 Standard Commercial Lines: Net premiums earned: General liability $ 273,415 243,349 Commercial automobile 251,720 217,371 Commercial property 161,553 135,292 Workers compensation 87,777 84,184 Businessowners' policies 39,921 33,171 Bonds 12,088 11,397 Other 7,636 6,851 Miscellaneous income 7,134 2,181 Total Standard Commercial Lines revenue 841,244 733,796 Standard Personal Lines: Net premiums earned: Personal automobile 56,960 44,914 Homeowners 44,113 35,013 Other 2,773 1,943 Miscellaneous income 640 453 Total Standard Personal Lines revenue 104,486 82,323 E&S Lines: Net premiums earned: Casualty lines 71,638 60,817 Property lines 41,350 28,034 Miscellaneous income 27 — Total E&S Lines revenue 113,015 88,851 Investments: Net investment income earned 107,849 91,506 Net realized and unrealized investment gains (losses) (1,635) 3,344 Total Investments revenue 106,214 94,850 Total revenues $ 1,164,959 999,820 Income Before and After Federal Income Tax Quarter ended March 31, ($ in thousands) 2024 2023 Standard Commercial Lines: Underwriting income (loss), before federal income tax $ 10,381 38,921 Underwriting income (loss), after federal income tax 8,201 30,748 Combined ratio 98.8 % 94.7 ROE contribution 1.2 5.1 Standard Personal Lines: Underwriting income (loss), before federal income tax $ (5,335) (13,073) Underwriting income (loss), after federal income tax (4,215) (10,328) Combined ratio 105.1 % 116.0 ROE contribution (0.6) (1.7) E&S Lines: Underwriting income (loss), before federal income tax $ 13,985 13,335 Underwriting income (loss), after federal income tax 11,048 10,535 Combined ratio 87.6 % 85.0 ROE contribution 1.6 1.8 Investments: Net investment income earned $ 107,849 91,506 Net realized and unrealized investment gains (losses) (1,635) 3,344 Total investments segment income, before federal income tax 106,214 94,850 Tax on investments segment income 21,866 19,156 Total investments segment income, after federal income tax $ 84,348 75,694 ROE contribution of after-tax net investment income earned 12.3 12.2 Reconciliation of Segment Results to Income Before Federal Income Tax Quarter ended March 31, ($ in thousands) 2024 2023 Underwriting income (loss) Standard Commercial Lines $ 10,381 38,921 Standard Personal Lines (5,335) (13,073) E&S Lines 13,985 13,335 Investment income 106,214 94,850 Total all segments 125,245 134,033 Interest expense (7,181) (7,166) Corporate expenses (15,498) (12,108) Income, before federal income tax $ 102,566 114,759 Preferred stock dividends (2,300) (2,300) Income available to common stockholders, before federal income tax $ 100,266 112,459

Retirement Plans

Retirement Plans	3 Months Ended
	Mar. 31, 2024
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans The primary pension plan for our employees is the Retirement Income Plan for Selective Insurance Company of America (the “Pension Plan”). The plan is closed to new entrants, and benefits ceased accruing under the Pension Plan after March 31, 2016. For more information about Selective Insurance Company of America's ("SICA") retirement plans, see Note 15. “Retirement Plans” in Item 8. “Financial Statements and Supplementary Data.” of our 2023 Annual Report. The following tables provide information about the Pension Plan: Pension Plan Quarter ended March 31, ($ in thousands) 2024 2023 Net Periodic Pension Cost (Benefit): Interest cost $ 3,888 3,866 Expected return on plan assets (5,382) (5,773) Amortization of unrecognized net actuarial loss 955 751 Total net periodic pension cost (benefit) 1 $ (539) (1,156) 1 The components of net periodic pension cost (benefit) are included within "Loss and loss expense incurred" and "Other insurance expenses" on the Consolidated Statements of Income. Pension Plan Quarter ended March 31, 2024 2023 Weighted-Average Expense Assumptions: Discount rate 5.02 % 5.21 % Effective interest rate for calculation of interest cost 4.91 5.09 Expected return on plan assets 6.40 6.90

Comprehensive Income

Comprehensive Income	3 Months Ended
	Mar. 31, 2024
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Comprehensive Income	Comprehensive Income The components of comprehensive income, both gross and net of tax, for First Quarter 2024 and First Quarter 2023 were as follows: First Quarter 2024 ($ in thousands) Gross Tax Net Net income $ 102,566 20,048 82,518 Components of OCI: Unrealized gains (losses) on investment securities : Unrealized holding gains (losses) during the period (15,560) (3,267) (12,293) Unrealized gains (losses) on securities with credit loss recognized in earnings (3,132) (658) (2,474) Amounts reclassified into net income: Net realized (gains) losses on disposals and intent-to-sell AFS securities (78) (17) (61) Credit loss (benefit) expense 2,650 557 2,093 Total unrealized gains (losses) on investment securities (16,120) (3,385) (12,735) Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial (gain) loss 967 203 764 Total defined benefit pension and post-retirement plans 967 203 764 Other comprehensive income (loss) (15,153) (3,182) (11,971) Comprehensive income (loss) $ 87,413 16,866 70,547 First Quarter 2023 ($ in thousands) Gross Tax Net Net income $ 114,759 22,185 92,574 Components of OCI: Unrealized gains (losses) on investment securities: Unrealized holding gains (losses) during the period 65,925 13,846 52,079 Unrealized gains (losses) on securities with credit loss recognized in earnings 22,431 4,710 17,721 Amounts reclassified into net income: Net realized (gains) losses on disposals and intent-to-sell AFS securities 6,104 1,282 4,822 Credit loss (benefit) expense (9,529) (2,002) (7,527) Total unrealized gains (losses) on investment securities 84,931 17,836 67,095 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial (gain) loss 757 159 598 Total defined benefit pension and post-retirement plans 757 159 598 Other comprehensive income (loss) 85,688 17,995 67,693 Comprehensive income (loss) $ 200,447 40,180 160,267 The balances of, and changes in, each component of accumulated other comprehensive income (loss) ("AOCI") (net of taxes) as of March 31, 2024, were as follows: March 31, 2024 Net Unrealized Gains (Losses) on Investment Securities Defined Benefit Pension and Post-Retirement Plans Total AOCI ($ in thousands) Credit Loss Related 1 All Investments Balance, December 31, 2023 $ (84,442) (194,628) (279,070) (93,931) (373,001) OCI before reclassifications (2,474) (12,293) (14,767) — (14,767) Amounts reclassified from AOCI 2,093 (61) 2,032 764 2,796 Net current period OCI (381) (12,354) (12,735) 764 (11,971) Balance, March 31, 2024 $ (84,823) (206,982) (291,805) (93,167) (384,972) 1 Represents change in unrealized gains (losses) on securities with credit loss recognized in earnings. The reclassifications out of AOCI were as follows: Quarter ended March 31, Affected Line Item in the Unaudited Consolidated Statements of Income ($ in thousands) 2024 2023 Net realized (gains) losses on disposals and intent-to-sell AFS securities Net realized (gains) losses $ (78) 6,104 Net realized and unrealized investment gains (losses) Tax (benefit) expense 17 (1,282) Total federal income tax expense Net of taxes (61) 4,822 Net income Credit loss related Credit loss (benefit) expense 2,650 (9,529) Net realized and unrealized investment gains (losses) Tax (benefit) expense (557) 2,002 Total federal income tax expense Net of taxes 2,093 (7,527) Net income Defined benefit pension and post-retirement life plans Net actuarial loss 222 175 Loss and loss expense incurred Net actuarial loss 745 582 Other insurance expenses Total 967 757 Income before federal income tax Tax (benefit) expense (203) (159) Total federal income tax expense Net of taxes 764 598 Net income Total reclassifications for the period $ 2,796 (2,107) Net income

Earnings per Common Share

Earnings per Common Share	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Earnings per Common Share	Earnings per Common Share The following table presents the calculations of earnings per common share ("EPS") on a basic and diluted basis: Quarter ended March 31, (in thousands, except per share amounts) 2024 2023 Net income available to common stockholders: $ 80,218 90,274 Weighted average common shares outstanding: Weighted average common shares outstanding - basic 60,827 60,536 Effect of dilutive securities - stock compensation plans 386 372 Weighted average common shares outstanding - diluted 61,213 60,908 EPS: Basic $ 1.32 1.49 Diluted 1.31 1.48

Litigation

Litigation	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Litigation	Litigation As of March 31, 2024, we do not believe we are involved in any legal action that could have a material adverse effect on our consolidated financial condition, results of operations, or cash flows. In the ordinary course of conducting business, we are parties in various legal actions. Most are claims litigation involving our ten insurance subsidiaries (collectively referred to as "Insurance Subsidiaries") as (i) liability insurers defending or providing indemnity for third-party claims brought against our customers, (ii) insurers defending first-party coverage claims brought against them, or (iii) liability insurers seeking declaratory judgment on our insurance coverage obligations. We account for such activity by establishing unpaid loss and loss expense reserves. Considering potential losses and defense costs reserves, we expect that any potential ultimate liability for ordinary course claims litigation will not be material to our consolidated financial condition, results of operations, or cash flows. All our commercial property and businessowners' policies require direct physical loss of or damage to property by a covered cause of loss. All our standard lines commercial property and businessowners' policies also include or attach an exclusion that states all loss or property damage caused by or resulting from any virus, bacterium, or other microorganism that induces or is capable of inducing physical distress, illness, or disease is not a covered cause of loss ("Virus Exclusion"). Whether COVID-19-related contamination, the existence of the COVID-19 pandemic, and the resulting COVID-19-related government shutdown orders cause physical loss of or damage to property is the subject of much public debate and first-party coverage litigation against some insurers, including us. The Virus Exclusion is also the subject of first-party coverage litigation against some insurers, including us. To date, insurers (including us) have prevailed in the majority of these suits, with most decisions holding that COVID-19 does not cause physical loss of or damage to property and the Virus Exclusion is valid. Nonetheless, these two matters continue to be litigated in trial courts, are subject to review by state and federal appellate courts, and their ultimate outcome cannot be assured. From time to time, our Insurance Subsidiaries also are named as defendants in other legal actions, some asserting claims for substantial amounts. Plaintiffs may style these actions as class actions and seek judicial certification of a state or national class for allegations involving our business practices, such as improper medical provider reimbursement under workers compensation and personal and commercial automobile insurance policies or improper reimbursement for automobile parts. Similarly, our Insurance Subsidiaries can be named defendants in individual actions seeking extra-contractual damages, punitive damages, or penalties, often alleging bad faith in handling insurance claims. We believe that we have valid defenses to these allegations and account for such activity by establishing unpaid loss and loss expense reserves. Considering estimated losses and defense costs reserves, we expect that any potential ultimate liability for these other legal actions will not be material to our consolidated financial condition. As litigation outcomes are inherently unpredictable and the amounts sought in certain actions are large or indeterminate, adverse outcomes could potentially have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net income	$ 82,518	$ 92,574

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Statements of Cash Flows (Table

Statements of Cash Flows (Tables)	3 Months Ended
	Mar. 31, 2024
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Supplemental cash flow information was as follows: Quarter ended March 31, ($ in thousands) 2024 2023 Cash paid (received) during the period for: Interest $ 8,544 8,528 Federal income tax — — Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases 1,777 2,235 Operating cash flows from financing leases 22 11 Financing cash flows from finance leases 731 615 Non-cash items: Corporate actions related to fixed income securities, available-for-sale ("AFS") 1 2,298 4,629 Assets acquired under finance lease arrangements 3 — Assets acquired under operating lease arrangements 674 4,237 Non-cash purchase of property and equipment 8 23 1 Examples of corporate actions include like-kind exchanges, non-cash acquisitions, and stock splits.
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash and restricted cash reported within the Consolidated Balance Sheets that equate to the amount reported in the Consolidated Statements of Cash Flows: ($ in thousands) March 31, 2024 December 31, 2023 Cash $ 124 180 Restricted cash 11,720 13,092 Total cash and restricted cash shown in the Consolidated Statements of Cash Flows $ 11,844 13,272
Schedule of Restrictions on Cash and Cash Equivalents	The following table provides a reconciliation of cash and restricted cash reported within the Consolidated Balance Sheets that equate to the amount reported in the Consolidated Statements of Cash Flows: ($ in thousands) March 31, 2024 December 31, 2023 Cash $ 124 180 Restricted cash 11,720 13,092 Total cash and restricted cash shown in the Consolidated Statements of Cash Flows $ 11,844 13,272

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2024
Investments [Abstract]
Schedule of Available-for-Sale Securities	Information regarding our AFS securities as of March 31, 2024 and December 31, 2023, were as follows: March 31, 2024 Cost/ Allowance for Credit Losses Unrealized Unrealized Fair ($ in thousands) AFS fixed income securities: U.S. government and government agencies $ 161,335 — 70 (19,579) 141,826 Foreign government 10,703 (29) — (1,445) 9,229 Obligations of states and political subdivisions 570,438 (695) 1,101 (31,858) 538,986 Corporate securities 2,930,310 (15,442) 20,367 (140,185) 2,795,050 Collateralized loan obligations ("CLO") and other asset-backed securities ("ABS") 1,958,551 (2,627) 15,158 (73,997) 1,897,085 Residential mortgage-backed securities ("RMBS") 1,623,948 (11,580) 3,828 (104,237) 1,511,959 Commercial mortgage-backed securities ("CMBS") 727,986 (8) 1,103 (39,712) 689,369 Total AFS fixed income securities $ 7,983,271 (30,381) 41,627 (411,013) 7,583,504 December 31, 2023 Cost/ Allowance for Credit Losses Unrealized Unrealized Fair ($ in thousands) AFS fixed income securities: U.S. government and government agencies $ 223,157 — 139 (18,261) 205,035 Foreign government 11,140 (35) — (1,302) 9,803 Obligations of states and political subdivisions 612,938 (669) 2,623 (28,927) 585,965 Corporate securities 2,834,048 (12,999) 28,078 (137,888) 2,711,239 CLO and other ABS 1,911,831 (2,854) 11,855 (86,005) 1,834,827 RMBS 1,568,960 (11,649) 6,023 (85,851) 1,477,483 CMBS 718,623 (6) 1,358 (45,130) 674,845 Total AFS fixed income securities $ 7,880,697 (28,212) 50,076 (403,364) 7,499,197
Schedule of Debt Securities, Available-for-Sale, Allowance for Credit Loss	The following tables provide a roll forward of the allowance for credit losses on our AFS fixed income securities for the indicated periods: Quarter ended March 31, 2024 Beginning Balance Current Provision for Securities without Prior Allowance Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance ($ in thousands) Foreign government $ 35 — — — (6) — 29 Obligations of states and political subdivisions 669 9 — 25 (8) — 695 Corporate securities 12,999 1,015 — 1,792 (355) (9) 15,442 CLO and other ABS 2,854 90 — (314) (3) — 2,627 RMBS 11,649 — — 31 (100) — 11,580 CMBS 6 2 — — — — 8 Total AFS fixed income securities $ 28,212 1,116 — 1,534 (472) (9) 30,381 Quarter ended March 31, 2023 Beginning Balance Current Provision for Securities without Prior Allowance Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance ($ in thousands) Foreign government $ 284 — — (248) — — 36 Obligations of states and political subdivisions 1,024 50 — (254) (83) — 737 Corporate securities 30,330 2,854 — (13,964) (2,453) (11) 16,756 CLO and other ABS 2,375 787 — 736 (3) — 3,895 RMBS 11,597 12 — 219 (88) — 11,740 CMBS 111 27 — 252 — — 390 Total AFS fixed income securities $ 45,721 3,730 — (13,259) (2,627) (11) 33,554
Schedule of Quantitative Information about Unrealized Losses on AFS	Quantitative information about unrealized losses on our AFS portfolio follows: March 31, 2024 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: U.S. government and government agencies $ 8,149 (49) 107,151 (19,530) 115,300 (19,579) Foreign government — — 9,229 (1,445) 9,229 (1,445) Obligations of states and political subdivisions 161,084 (1,289) 303,259 (30,569) 464,343 (31,858) Corporate securities 316,330 (4,043) 1,446,157 (136,142) 1,762,487 (140,185) CLO and other ABS 385,471 (7,527) 824,843 (66,470) 1,210,314 (73,997) RMBS 511,009 (8,770) 761,356 (95,467) 1,272,365 (104,237) CMBS 133,266 (2,033) 494,395 (37,679) 627,661 (39,712) Total AFS fixed income securities $ 1,515,309 (23,711) 3,946,390 (387,302) 5,461,699 (411,013) December 31, 2023 Less than 12 months 12 months or longer Total ($ in thousands) Fair Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: U.S. government and government agencies $ 77,698 (188) 108,578 (18,073) 186,276 (18,261) Foreign government 1,552 (87) 8,251 (1,215) 9,803 (1,302) Obligations of states and political subdivisions 137,031 (962) 290,964 (27,965) 427,995 (28,927) Corporate securities 263,423 (6,369) 1,439,422 (131,519) 1,702,845 (137,888) CLO and other ABS 278,940 (7,120) 984,175 (78,885) 1,263,115 (86,005) RMBS 351,976 (4,765) 757,914 (81,086) 1,109,890 (85,851) CMBS 130,189 (2,995) 471,256 (42,135) 601,445 (45,130) Total AFS fixed income securities $ 1,240,809 (22,486) 4,060,560 (380,878) 5,301,369 (403,364)
Schedule of Fixed Maturity Securities by Contractual Maturities	AFS and held-to-maturity ("HTM") fixed income securities at March 31, 2024, by contractual maturity are shown below. The maturities of RMBS, CMBS, CLO and other ABS securities were calculated using each security's estimated average life. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. AFS HTM ($ in thousands) Fair Value Carrying Value Fair Value Due in one year or less $ 582,163 — — Due after one year through five years 3,435,983 15,716 14,898 Due after five years through 10 years 2,833,659 4,579 4,285 Due after 10 years 731,699 — — Total fixed income securities $ 7,583,504 20,295 19,183
Schedule of Alternative Investment Portfolio by Strategyand Remaining Commitment Amount and Maximum Exposure to Loss Associated with Each Strategy	The following table summarizes our alternative investment portfolio by strategy: March 31, 2024 December 31, 2023 ($ in thousands) Carrying Value Remaining Commitment Maximum Exposure to Loss Carrying Value Remaining Commitment Maximum Exposure to Loss Alternative Investments Private equity $ 306,444 137,986 444,430 301,759 131,885 433,644 Private credit 53,392 90,569 143,961 54,500 89,401 143,901 Real assets 42,853 31,100 73,953 39,520 33,040 72,560 Total alternative investments $ 402,689 259,655 662,344 395,779 254,326 650,105
Schedule of Aggregated Summarized Income Statement Financial Information for Partnerships in Alternative Investment Portfolio	The following table shows gross summarized financial information for our alternative investments portfolio, including the portion we do not own. As the majority of these investments report results to us on a one quarter lag, the summarized financial statement information is for the three-month period ended December 31: Income Statement Information Quarter ended March 31, ($ in millions) 2024 2023 Net investment income (loss) $ (346.0) (70.7) Realized gains 1,830.8 1,722.3 Net change in unrealized appreciation (depreciation) 3,819.0 1,443.7 Net income $ 5,303.8 3,095.3 Alternative investment income included in "Net investment income earned" on our Consolidated Statements of Income $ 6.9 7.8
Schedule of Securities Pledged as Collateral	The following table summarizes the market value of these securities at March 31, 2024: ($ in millions) FHLBI Collateral FHLBNY Collateral State and Total U.S. government and government agencies $ — — 20.0 20.0 Obligations of states and political subdivisions — — 4.2 4.2 RMBS 66.2 24.1 — 90.3 CMBS 2.3 8.5 — 10.8 Total pledged as collateral $ 68.5 32.6 24.2 125.3
Schedule of Pre-Tax Net Investment Income Earned	The components of pre-tax net investment income earned were as follows: Quarter ended March 31, ($ in thousands) 2024 2023 Fixed income securities $ 94,102 80,087 Commercial mortgage loans ("CMLs") 2,794 1,965 Equity securities 4,908 1,205 Short-term investments 3,519 4,650 Alternative investments 6,881 7,768 Other investments 263 43 Investment expenses (4,618) (4,212) Net investment income earned $ 107,849 91,506
Schedule of Realized and Unrealized Gains (Losses) on Securities	The following table summarizes net realized and unrealized investment gains and losses for the periods indicated: Quarter ended March 31, ($ in thousands) 2024 2023 Gross gains on sales $ 2,135 3,784 Gross losses on sales (1,965) (12,930) Net realized gains (losses) on disposals 170 (9,146) Net unrealized gains (losses) on equity securities 692 3,248 Net credit loss benefit (expense) on fixed income securities, AFS (2,650) 9,529 Net credit loss benefit (expense) on CMLs 168 17 Losses on securities for which we have the intent to sell (15) (304) Net realized and unrealized investment gains (losses) $ (1,635) 3,344
Schedule of Unrealized Gain (Loss) on Equity Securities	Net unrealized gains and losses recognized in income on equity securities, as reflected in the table above, included the following: Quarter ended March 31, ($ in thousands) 2024 2023 Unrealized gains (losses) recognized in income on equity securities: On securities remaining in our portfolio at end of period $ 692 (142) On securities sold in period — 3,390 Total unrealized gains (losses) recognized in income on equity securities $ 692 3,248

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Carrying Values and Estimated Fair Values of Financial Liabilities	The following table presents the carrying amounts and fair values of our financial liabilities as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 ($ in thousands) Carrying Amount Fair Value Carrying Amount Fair Value Financial Liabilities Long-term debt: 7.25% Senior Notes $ 49,927 51,137 49,926 53,047 6.70% Senior Notes 99,571 101,666 99,565 104,039 5.375% Senior Notes 294,548 286,927 294,523 288,787 3.03% borrowings from FHLBI 60,000 57,568 60,000 57,932 Subtotal long-term debt 504,046 497,298 504,014 503,805 Unamortized debt issuance costs (2,650) (2,704) Finance lease obligations 1,909 2,636 Total long-term debt $ 503,305 503,946
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables provide quantitative disclosures of our financial assets that were measured and recorded at fair value at March 31, 2024, and December 31, 2023: March 31, 2024 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in Significant Other Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 141,826 33,530 108,296 — Foreign government 9,229 — 9,229 — Obligations of states and political subdivisions 538,986 — 531,239 7,747 Corporate securities 2,795,050 — 2,507,554 287,496 CLO and other ABS 1,897,085 — 1,636,988 260,097 RMBS 1,511,959 — 1,511,959 — CMBS 689,369 — 689,014 355 Total AFS fixed income securities 7,583,504 33,530 6,994,279 555,695 Equity securities: Common stock 1 192,510 36,333 — 1,067 Preferred stock 1,810 1,810 — — Total equity securities 194,320 38,143 — 1,067 Short-term investments 247,883 246,904 979 — Total assets measured at fair value $ 8,025,707 318,577 6,995,258 556,762 December 31, 2023 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in Significant Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 205,035 34,056 170,979 — Foreign government 9,803 — 9,803 — Obligations of states and political subdivisions 585,965 — 578,131 7,834 Corporate securities 2,711,239 — 2,413,907 297,332 CLO and other ABS 1,834,827 — 1,589,514 245,313 RMBS 1,477,483 — 1,477,483 — CMBS 674,845 — 674,489 356 Total AFS fixed income securities 7,499,197 34,056 6,914,306 550,835 Equity securities: Common stock 1 185,339 20,582 — 854 Preferred stock 1,816 1,816 — — Total equity securities 187,155 22,398 — 854 Short-term investments 309,317 308,512 805 — Total assets measured at fair value $ 7,995,669 364,966 6,915,111 551,689 1
Schedule of Summary of the Changes in Fair Value of Securities Using Level 3 Inputs	The following tables provide a summary of Level 3 changes in First Quarter 2024 and First Quarter 2023: March 31, 2024 ($ in thousands) Obligations of States and Political Subdivisions Corporate Securities CLO and Other ABS CMBS Common Stock Total Fair value, December 31, 2023 $ 7,834 297,332 245,313 356 854 551,689 Total net gains (losses) for the period included in: Other comprehensive income (loss) ("OCI") (86) (376) 399 3 — (60) Net realized and unrealized gains (losses) (1) 140 57 — 213 409 Net investment income earned — 280 (1) (1) — 278 Purchases — 1,152 14,658 — — 15,810 Sales — — — — — — Issuances — — — — — — Settlements — (2,870) (1,173) (3) — (4,046) Transfers into Level 3 — 20,065 19,537 — — 39,602 Transfers out of Level 3 — (28,227) (18,693) — — (46,920) Fair value, March 31, 2024 $ 7,747 287,496 260,097 355 1,067 556,762 Change in unrealized gains (losses) for the period included in earnings for assets held at period end (1) 140 57 — 213 409 Change in unrealized gains (losses) for the period included in OCI for assets held at period end (86) (376) 399 3 — (60) March 31, 2023 ($ in thousands) Obligation of state and Political Subdivisions Corporate Securities CLO and Other ABS CMBS Common Stock Total Fair value, December 31, 2022 $ 6,661 187,980 153,342 375 897 349,255 Total net gains (losses) for the period included in: OCI 152 2,405 696 17 — 3,270 Net realized and unrealized gains (losses) 61 72 (73) — (269) (209) Net investment income earned — 12 (32) (1) — (21) Purchases — 24,799 13,403 — — 38,202 Sales — — — — — — Issuances — — — — — — Settlements — (4,044) (1,192) (3) — (5,239) Transfers into Level 3 — 361 14,148 2,848 — 17,357 Transfers out of Level 3 — — (534) — — (534) Fair value, March 31, 2023 $ 6,874 211,585 179,758 3,236 628 402,081 Change in unrealized gains (losses) for the period included in earnings for assets held at period end 61 72 (73) — (269) (209) Change in unrealized gains (losses) for the period included in OCI for assets held at period end 152 2,405 696 17 — 3,270
Schedule of Fair Value Measurement Inputs and Valuation Techniques	The following tables present quantitative information about the significant unobservable inputs used in the fair value measurements of Level 3 assets at March 31, 2024, and December 31, 2023: March 31, 2024 ($ in thousands) Assets Measured at Fair Value Valuation Techniques Unobservable Inputs Range Weighted Average Internal valuations: Corporate securities $ 155,633 Discounted Cash Flow Illiquidity Spread (4.4)% - 5.3% 1.8% CLO and other ABS 155,287 Discounted Cash Flow Illiquidity Spread 0.01% - 19.6% 2.4% Total internal valuations 310,920 Other 1 245,842 Total Level 3 securities $ 556,762 December 31, 2023 ($ in thousands) Assets Measured at Fair Value Valuation Techniques Unobservable Inputs Range Weighted Average Internal valuations: Corporate securities $ 135,524 Discounted Cash Flow Illiquidity Spread (4.4)% - 5.3% 1.9% CLO and other ABS 127,210 Discounted Cash Flow Illiquidity Spread 0.01% - 19.6% 2.4% Total internal valuations 262,734 Other 1 288,955 Total Level 3 securities $ 551,689 1
Schedule of Quantitative Information of Financial Assets and Liabilities, Disclosed at Fair Value	The following tables provide quantitative information about our financial assets and liabilities that were not measured at fair value, but were disclosed as such at March 31, 2024, and December 31, 2023: March 31, 2024 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Corporate securities $ 19,183 — 19,183 — Total HTM fixed income securities 19,183 — 19,183 — CMLs $ 197,807 — — 197,807 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 51,137 — 51,137 — 6.70% Senior Notes 101,666 — 101,666 — 5.375% Senior Notes 286,927 — 286,927 — 3.03% borrowings from FHLBI 57,568 — 57,568 — Total long-term debt $ 497,298 — 497,298 — December 31, 2023 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Corporate securities 21,923 — 21,923 — Total HTM fixed income securities $ 21,923 — 21,923 — CMLs $ 178,913 — — 178,913 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 53,047 — 53,047 — 6.70% Senior Notes 104,039 — 104,039 — 5.375% Senior Notes 288,787 — 288,787 — 3.03% borrowings from FHLBI 57,932 — 57,932 — Total long-term debt $ 503,805 — 503,805 —

Allowance for Credit Losses o_2

Allowance for Credit Losses on Premiums Receivable (Tables)	3 Months Ended
	Mar. 31, 2024
Premiums Receivable Disclosure [Abstract]
Schedule of Allowance for Credit Losses on Premiums Receivable	The following table provides a roll forward of the allowance for credit losses on our premiums receivable balance for the indicated periods: Quarter ended March 31, ($ in thousands) 2024 2023 Balance at beginning of period $ 18,900 16,100 Current period change for expected credit losses 1,784 1,910 Write-offs charged against the allowance for credit losses (1,056) (1,164) Recoveries 372 254 Allowance for credit losses, end of period $ 20,000 17,100

Reinsurance (Tables)

Reinsurance (Tables)	3 Months Ended
	Mar. 31, 2024
Reinsurance Disclosures [Abstract]
Schedule of Reinsurance Recoverable, Credit Quality Indicator	The following tables provide (i) a disaggregation of our reinsurance recoverable balance by financial strength rating, and (ii) an aging analysis of our past due reinsurance recoverable balances as of March 31, 2024, and December 31, 2023: March 31, 2024 ($ in thousands) Current Past Due Total Reinsurance Recoverables Financial strength rating of rated reinsurers A++ $ 83,372 53 83,425 A+ 366,428 1,172 367,600 A 115,086 582 115,668 A- 3,865 89 3,954 Total rated reinsurers 568,751 1,896 570,647 Non-rated reinsurers Federal and state pools 77,799 — 77,799 Other than federal and state pools 4,135 504 4,639 Total non-rated reinsurers 81,934 504 82,438 Total reinsurance recoverable, gross $ 650,685 2,400 653,085 Less: allowance for credit losses (1,700) Total reinsurance recoverable, net 651,385 December 31, 2023 ($ in thousands) Current Past Due Total Reinsurance Recoverables Financial strength rating of rated reinsurers A++ $ 82,466 21 82,487 A+ 371,132 2,887 374,019 A 111,883 1,380 113,263 A- 3,596 89 3,685 Total rated reinsurers 569,077 4,377 573,454 Non-rated reinsurers Federal and state pools 80,506 — 80,506 Other than federal and state pools 4,488 77 4,565 Total non-rated reinsurers 84,994 77 85,071 Total reinsurance recoverable, gross $ 654,071 4,454 658,525 Less: allowance for credit losses (1,700) Total reinsurance recoverable, net 656,825
Schedule of Reinsurance Recoverable, Allowance for Credit Loss	The following table provides a roll forward of the allowance for credit losses on our reinsurance recoverable balance for the periods indicated: Quarter ended March 31, ($ in thousands) 2024 2023 Balance at beginning of period $ 1,700 1,600 Current period change for expected credit losses — 700 Write-offs charged against the allowance for credit losses — — Recoveries — — Allowance for credit losses, end of period $ 1,700 2,300
Schedule of List of Direct, Assumed, and Ceded Reinsurance Amounts	The following table lists direct, assumed, and ceded reinsurance amounts for premiums written, premiums earned, and loss and loss expense incurred for the indicated periods. For more information about reinsurance, refer to Note 9. “Reinsurance” in Item 8. “Financial Statements and Supplementary Data.” of our 2023 Annual Report. Quarter ended March 31, ($ in thousands) 2024 2023 Premiums written: Direct $ 1,315,911 1,132,760 Assumed 5,985 5,394 Ceded (165,275) (138,386) Net 1,156,621 999,768 Premiums earned: Direct 1,205,368 1,032,228 Assumed 6,191 6,290 Ceded (160,615) (136,182) Net 1,050,944 902,336 Loss and loss expense incurred: Direct 753,567 613,229 Assumed 5,981 5,255 Ceded (55,256) (51,046) Net $ 704,292 567,438

Reserve for Loss and Loss Exp_2

Reserve for Loss and Loss Expense (Tables)	3 Months Ended
	Mar. 31, 2024
Insurance Loss Reserves [Abstract]
Schedule of Roll Forward of Reserve for Loss and Loss Expense	The table below provides a roll forward of the reserve for loss and loss expense for beginning and ending reserve balances: Quarter ended March 31, ($ in thousands) 2024 2023 Gross reserve for loss and loss expense, at beginning of period $ 5,336,911 5,144,821 Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of period 618,601 757,513 Net reserve for loss and loss expense, at beginning of period 4,718,310 4,387,308 Incurred loss and loss expense for claims occurring in the: Current year 688,519 580,408 Prior years 15,773 (12,970) Total incurred loss and loss expense 704,292 567,438 Paid loss and loss expense for claims occurring in the: Current year 107,719 91,011 Prior years 435,489 418,194 Total paid loss and loss expense 543,208 509,205 Net reserve for loss and loss expense, at end of period 4,879,394 4,445,541 Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 622,356 653,909 Gross reserve for loss and loss expense, at end of period $ 5,501,750 5,099,450

Segment Information - (Tables)

Segment Information - (Tables)	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Schedule of Revenue By Segment	Revenue by Segment Quarter ended March 31, ($ in thousands) 2024 2023 Standard Commercial Lines: Net premiums earned: General liability $ 273,415 243,349 Commercial automobile 251,720 217,371 Commercial property 161,553 135,292 Workers compensation 87,777 84,184 Businessowners' policies 39,921 33,171 Bonds 12,088 11,397 Other 7,636 6,851 Miscellaneous income 7,134 2,181 Total Standard Commercial Lines revenue 841,244 733,796 Standard Personal Lines: Net premiums earned: Personal automobile 56,960 44,914 Homeowners 44,113 35,013 Other 2,773 1,943 Miscellaneous income 640 453 Total Standard Personal Lines revenue 104,486 82,323 E&S Lines: Net premiums earned: Casualty lines 71,638 60,817 Property lines 41,350 28,034 Miscellaneous income 27 — Total E&S Lines revenue 113,015 88,851 Investments: Net investment income earned 107,849 91,506 Net realized and unrealized investment gains (losses) (1,635) 3,344 Total Investments revenue 106,214 94,850 Total revenues $ 1,164,959 999,820
Schedule of Income Before and After Federal Income Tax	Income Before and After Federal Income Tax Quarter ended March 31, ($ in thousands) 2024 2023 Standard Commercial Lines: Underwriting income (loss), before federal income tax $ 10,381 38,921 Underwriting income (loss), after federal income tax 8,201 30,748 Combined ratio 98.8 % 94.7 ROE contribution 1.2 5.1 Standard Personal Lines: Underwriting income (loss), before federal income tax $ (5,335) (13,073) Underwriting income (loss), after federal income tax (4,215) (10,328) Combined ratio 105.1 % 116.0 ROE contribution (0.6) (1.7) E&S Lines: Underwriting income (loss), before federal income tax $ 13,985 13,335 Underwriting income (loss), after federal income tax 11,048 10,535 Combined ratio 87.6 % 85.0 ROE contribution 1.6 1.8 Investments: Net investment income earned $ 107,849 91,506 Net realized and unrealized investment gains (losses) (1,635) 3,344 Total investments segment income, before federal income tax 106,214 94,850 Tax on investments segment income 21,866 19,156 Total investments segment income, after federal income tax $ 84,348 75,694 ROE contribution of after-tax net investment income earned 12.3 12.2
Schedule of Reconciliation of Segment Results to Income Before Federal Income Tax	Reconciliation of Segment Results to Income Before Federal Income Tax Quarter ended March 31, ($ in thousands) 2024 2023 Underwriting income (loss) Standard Commercial Lines $ 10,381 38,921 Standard Personal Lines (5,335) (13,073) E&S Lines 13,985 13,335 Investment income 106,214 94,850 Total all segments 125,245 134,033 Interest expense (7,181) (7,166) Corporate expenses (15,498) (12,108) Income, before federal income tax $ 102,566 114,759 Preferred stock dividends (2,300) (2,300) Income available to common stockholders, before federal income tax $ 100,266 112,459

Retirement Plans (Table)

Retirement Plans (Table)	3 Months Ended
	Mar. 31, 2024
Retirement Benefits [Abstract]
Schedule of Components of Net Periodic Benefit Cost	The following tables provide information about the Pension Plan: Pension Plan Quarter ended March 31, ($ in thousands) 2024 2023 Net Periodic Pension Cost (Benefit): Interest cost $ 3,888 3,866 Expected return on plan assets (5,382) (5,773) Amortization of unrecognized net actuarial loss 955 751 Total net periodic pension cost (benefit) 1 $ (539) (1,156) 1 The components of net periodic pension cost (benefit) are included within "Loss and loss expense incurred" and "Other insurance expenses" on the Consolidated Statements of Income.
Schedule of Weighted-Average Expense Assumptions	Pension Plan Quarter ended March 31, 2024 2023 Weighted-Average Expense Assumptions: Discount rate 5.02 % 5.21 % Effective interest rate for calculation of interest cost 4.91 5.09 Expected return on plan assets 6.40 6.90

Comprehensive Income (Tables)

Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2024
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Schedule of Components of Comprehensive Income-Gross and Net of Tax	The components of comprehensive income, both gross and net of tax, for First Quarter 2024 and First Quarter 2023 were as follows: First Quarter 2024 ($ in thousands) Gross Tax Net Net income $ 102,566 20,048 82,518 Components of OCI: Unrealized gains (losses) on investment securities : Unrealized holding gains (losses) during the period (15,560) (3,267) (12,293) Unrealized gains (losses) on securities with credit loss recognized in earnings (3,132) (658) (2,474) Amounts reclassified into net income: Net realized (gains) losses on disposals and intent-to-sell AFS securities (78) (17) (61) Credit loss (benefit) expense 2,650 557 2,093 Total unrealized gains (losses) on investment securities (16,120) (3,385) (12,735) Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial (gain) loss 967 203 764 Total defined benefit pension and post-retirement plans 967 203 764 Other comprehensive income (loss) (15,153) (3,182) (11,971) Comprehensive income (loss) $ 87,413 16,866 70,547 First Quarter 2023 ($ in thousands) Gross Tax Net Net income $ 114,759 22,185 92,574 Components of OCI: Unrealized gains (losses) on investment securities: Unrealized holding gains (losses) during the period 65,925 13,846 52,079 Unrealized gains (losses) on securities with credit loss recognized in earnings 22,431 4,710 17,721 Amounts reclassified into net income: Net realized (gains) losses on disposals and intent-to-sell AFS securities 6,104 1,282 4,822 Credit loss (benefit) expense (9,529) (2,002) (7,527) Total unrealized gains (losses) on investment securities 84,931 17,836 67,095 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial (gain) loss 757 159 598 Total defined benefit pension and post-retirement plans 757 159 598 Other comprehensive income (loss) 85,688 17,995 67,693 Comprehensive income (loss) $ 200,447 40,180 160,267
Schedule of Components of Accumulated Other Comprehensive Income Net of Tax	The balances of, and changes in, each component of accumulated other comprehensive income (loss) ("AOCI") (net of taxes) as of March 31, 2024, were as follows: March 31, 2024 Net Unrealized Gains (Losses) on Investment Securities Defined Benefit Pension and Post-Retirement Plans Total AOCI ($ in thousands) Credit Loss Related 1 All Investments Balance, December 31, 2023 $ (84,442) (194,628) (279,070) (93,931) (373,001) OCI before reclassifications (2,474) (12,293) (14,767) — (14,767) Amounts reclassified from AOCI 2,093 (61) 2,032 764 2,796 Net current period OCI (381) (12,354) (12,735) 764 (11,971) Balance, March 31, 2024 $ (84,823) (206,982) (291,805) (93,167) (384,972) 1 Represents change in unrealized gains (losses) on securities with credit loss recognized in earnings.
Schedule of Reclassifications of Accumulated Other Comprehensive Income	The reclassifications out of AOCI were as follows: Quarter ended March 31, Affected Line Item in the Unaudited Consolidated Statements of Income ($ in thousands) 2024 2023 Net realized (gains) losses on disposals and intent-to-sell AFS securities Net realized (gains) losses $ (78) 6,104 Net realized and unrealized investment gains (losses) Tax (benefit) expense 17 (1,282) Total federal income tax expense Net of taxes (61) 4,822 Net income Credit loss related Credit loss (benefit) expense 2,650 (9,529) Net realized and unrealized investment gains (losses) Tax (benefit) expense (557) 2,002 Total federal income tax expense Net of taxes 2,093 (7,527) Net income Defined benefit pension and post-retirement life plans Net actuarial loss 222 175 Loss and loss expense incurred Net actuarial loss 745 582 Other insurance expenses Total 967 757 Income before federal income tax Tax (benefit) expense (203) (159) Total federal income tax expense Net of taxes 764 598 Net income Total reclassifications for the period $ 2,796 (2,107) Net income

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Schedule of Earnings Per Common Share, Basic and Diluted	The following table presents the calculations of earnings per common share ("EPS") on a basic and diluted basis: Quarter ended March 31, (in thousands, except per share amounts) 2024 2023 Net income available to common stockholders: $ 80,218 90,274 Weighted average common shares outstanding: Weighted average common shares outstanding - basic 60,827 60,536 Effect of dilutive securities - stock compensation plans 386 372 Weighted average common shares outstanding - diluted 61,213 60,908 EPS: Basic $ 1.32 1.49 Diluted 1.31 1.48

Statements of Cash Flows - Cash

Statements of Cash Flows - Cash Flow Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Supplemental Cash Flow Information [Abstract]
Interest	$ 8,544	$ 8,528
Federal income tax	0	0
Operating cash flows from operating leases	1,777	2,235
Operating cash flows from financing leases	22	11
Financing cash flows from finance leases	731	615
Corporate actions related to fixed income securities, available-for-sale ("AFS")	2,298	4,629
Assets acquired under finance lease arrangements	3	0
Assets acquired under operating lease arrangements	674	4,237
Non-cash purchase of property and equipment	$ 8	$ 23

Statements of Cash Flows - Sche

Statements of Cash Flows - Schedule of Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Supplemental Cash Flow Information [Abstract]
Cash	$ 124	$ 180
Restricted cash	11,720	13,092
Total cash and restricted cash shown in the Consolidated Statements of Cash Flows	$ 11,844	$ 13,272	$ 35,665	$ 25,209

Investments - Available-For-Sal

Investments - Available-For-Sale Securities Disclosure (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	$ 7,983,271	$ 7,880,697
Allowance for Credit Losses	(30,381)	(28,212)	$ (33,554)	$ (45,721)
Unrealized Gains	41,627	50,076
Unrealized Losses	(411,013)	(403,364)
Fair Value	7,583,504	7,499,197
U.S. government and government agencies
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	161,335	223,157
Allowance for Credit Losses	0	0
Unrealized Gains	70	139
Unrealized Losses	(19,579)	(18,261)
Fair Value	141,826	205,035
Foreign government
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	10,703	11,140
Allowance for Credit Losses	(29)	(35)	(36)	(284)
Unrealized Gains	0	0
Unrealized Losses	(1,445)	(1,302)
Fair Value	9,229	9,803
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	570,438	612,938
Allowance for Credit Losses	(695)	(669)	(737)	(1,024)
Unrealized Gains	1,101	2,623
Unrealized Losses	(31,858)	(28,927)
Fair Value	538,986	585,965
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	2,930,310	2,834,048
Allowance for Credit Losses	(15,442)	(12,999)	(16,756)	(30,330)
Unrealized Gains	20,367	28,078
Unrealized Losses	(140,185)	(137,888)
Fair Value	2,795,050	2,711,239
Collateralized loan obligations ("CLO") and other asset-backed securities ("ABS")
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	1,958,551	1,911,831
Allowance for Credit Losses	(2,627)	(2,854)	(3,895)	(2,375)
Unrealized Gains	15,158	11,855
Unrealized Losses	(73,997)	(86,005)
Fair Value	1,897,085	1,834,827
Residential mortgage-backed securities ("RMBS")
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	1,623,948	1,568,960
Allowance for Credit Losses	(11,580)	(11,649)	(11,740)	(11,597)
Unrealized Gains	3,828	6,023
Unrealized Losses	(104,237)	(85,851)
Fair Value	1,511,959	1,477,483
Commercial mortgage-backed securities ("CMBS")
Debt Securities, Available-for-sale [Line Items]
Cost/ Amortized Cost	727,986	718,623
Allowance for Credit Losses	(8)	(6)	$ (390)	$ (111)
Unrealized Gains	1,103	1,358
Unrealized Losses	(39,712)	(45,130)
Fair Value	$ 689,369	$ 674,845

Investments - Available-for-S_2

Investments - Available-for-Sale Allowance for Credit Losses Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	$ 28,212	$ 45,721
Current Provision for Securities without Prior Allowance	1,116	3,730
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	1,534	(13,259)
Reductions for Securities Sold	(472)	(2,627)
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	(9)	(11)
Allowance for credit losses, period ending balance	30,381	33,554
Foreign government
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	35	284
Current Provision for Securities without Prior Allowance	0	0
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	0	(248)
Reductions for Securities Sold	(6)	0
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	0	0
Allowance for credit losses, period ending balance	29	36
Obligations of states and political subdivisions
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	669	1,024
Current Provision for Securities without Prior Allowance	9	50
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	25	(254)
Reductions for Securities Sold	(8)	(83)
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	0	0
Allowance for credit losses, period ending balance	695	737
Corporate securities
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	12,999	30,330
Current Provision for Securities without Prior Allowance	1,015	2,854
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	1,792	(13,964)
Reductions for Securities Sold	(355)	(2,453)
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	(9)	(11)
Allowance for credit losses, period ending balance	15,442	16,756
CLO and other ABS
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	2,854	2,375
Current Provision for Securities without Prior Allowance	90	787
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	(314)	736
Reductions for Securities Sold	(3)	(3)
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	0	0
Allowance for credit losses, period ending balance	2,627	3,895
RMBS
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	11,649	11,597
Current Provision for Securities without Prior Allowance	0	12
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	31	219
Reductions for Securities Sold	(100)	(88)
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	0	0
Allowance for credit losses, period ending balance	11,580	11,740
CMBS
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, period beginning balance	6	111
Current Provision for Securities without Prior Allowance	2	27
Initial Allowance for Purchased Credit Deteriorated Assets with Credit Deterioration	0	0
Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities	0	252
Reductions for Securities Sold	0	0
Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period	0	0
Allowance for credit losses, period ending balance	$ 8	$ 390

Investments - Accrued Investmen

Investments - Accrued Investment Income (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accrued Interest on Investments [Line Items]
Accrued investment income	$ 68,034	$ 66,339
Available-for-Sale Securities
Accrued Interest on Investments [Line Items]
Accrued investment income	$ 66,300	$ 64,600

Investments - Fair Value and Gr

Investments - Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
U.S. government and government agencies
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	$ 8,149	$ 77,698
AFS Unrealized Losses, Less than 12 months	(49)	(188)
AFS Fair Value, 12 months or longer	107,151	108,578
AFS Unrealized Losses, 12 months or longer	(19,530)	(18,073)
AFS Fair Value	115,300	186,276
AFS Unrealized Losses	(19,579)	(18,261)
Foreign government
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	0	1,552
AFS Unrealized Losses, Less than 12 months	0	(87)
AFS Fair Value, 12 months or longer	9,229	8,251
AFS Unrealized Losses, 12 months or longer	(1,445)	(1,215)
AFS Fair Value	9,229	9,803
AFS Unrealized Losses	(1,445)	(1,302)
Obligations of states and political subdivisions
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	161,084	137,031
AFS Unrealized Losses, Less than 12 months	(1,289)	(962)
AFS Fair Value, 12 months or longer	303,259	290,964
AFS Unrealized Losses, 12 months or longer	(30,569)	(27,965)
AFS Fair Value	464,343	427,995
AFS Unrealized Losses	(31,858)	(28,927)
Corporate securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	316,330	263,423
AFS Unrealized Losses, Less than 12 months	(4,043)	(6,369)
AFS Fair Value, 12 months or longer	1,446,157	1,439,422
AFS Unrealized Losses, 12 months or longer	(136,142)	(131,519)
AFS Fair Value	1,762,487	1,702,845
AFS Unrealized Losses	(140,185)	(137,888)
CLO and other ABS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	385,471	278,940
AFS Unrealized Losses, Less than 12 months	(7,527)	(7,120)
AFS Fair Value, 12 months or longer	824,843	984,175
AFS Unrealized Losses, 12 months or longer	(66,470)	(78,885)
AFS Fair Value	1,210,314	1,263,115
AFS Unrealized Losses	(73,997)	(86,005)
RMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	511,009	351,976
AFS Unrealized Losses, Less than 12 months	(8,770)	(4,765)
AFS Fair Value, 12 months or longer	761,356	757,914
AFS Unrealized Losses, 12 months or longer	(95,467)	(81,086)
AFS Fair Value	1,272,365	1,109,890
AFS Unrealized Losses	(104,237)	(85,851)
CMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	133,266	130,189
AFS Unrealized Losses, Less than 12 months	(2,033)	(2,995)
AFS Fair Value, 12 months or longer	494,395	471,256
AFS Unrealized Losses, 12 months or longer	(37,679)	(42,135)
AFS Fair Value	627,661	601,445
AFS Unrealized Losses	(39,712)	(45,130)
Available-for-Sale Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	1,515,309	1,240,809
AFS Unrealized Losses, Less than 12 months	(23,711)	(22,486)
AFS Fair Value, 12 months or longer	3,946,390	4,060,560
AFS Unrealized Losses, 12 months or longer	(387,302)	(380,878)
AFS Fair Value	5,461,699	5,301,369
AFS Unrealized Losses	$ (411,013)	$ (403,364)

Investments - Fixed Income Secu

Investments - Fixed Income Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
AFS, Fair Value
Due in one year or less fair value, AFS	$ 582,163
Due after one year through five years fair value, AFS	3,435,983
Due after five years through 10 years fair value, AFS	2,833,659
Due after 10 years fair value, AFS	731,699
Total AFS fixed income securities, Fair Value	7,583,504	$ 7,499,197
HTM, Carrying Value
Due in one year or less carrying value, HTM	0
Due after one year through five years carrying value, HTM	15,716
Due after five years through 10 years carrying value, HTM	4,579
Due after 10 years carrying value, HTM	0
Fixed income securities, held-to-maturity, net of allowance for credit losses	20,295	22,700
HTM, Fair Value
Due in one year or less fair value, HTM	0
Due after one year through five years fair value, HTM	14,898
Due after five years through 10 years fair value, HTM	4,285
Due after 10 years fair value, HTM	0
Total HTM fixed income securities, Fair Value	$ 19,183	$ 21,923

Investments - Alternative Inves

Investments - Alternative Investment Portfolio by Strategy and the Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy [Line Items]
Carrying Value	$ 402,689	$ 395,779
Private equity
Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy [Line Items]
Carrying Value	306,444	301,759
Remaining Commitment	137,986	131,885
Maximum Exposure to Loss	444,430	433,644
Private credit
Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy [Line Items]
Carrying Value	53,392	54,500
Remaining Commitment	90,569	89,401
Maximum Exposure to Loss	143,961	143,901
Real assets
Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy [Line Items]
Carrying Value	42,853	39,520
Remaining Commitment	31,100	33,040
Maximum Exposure to Loss	73,953	72,560
Alternative investments
Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy [Line Items]
Carrying Value	402,689	395,779
Remaining Commitment	259,655	254,326
Maximum Exposure to Loss	$ 662,344	$ 650,105

Investments - Aggregated Income

Investments - Aggregated Income Statement Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule of Equity Method Investments [Line Items]
Alternative investment income included in "Net investment income earned" on our Consolidated Statements of Income	$ 107,849	$ 91,506
Investments Accounted For Under The Equity Method
Schedule of Equity Method Investments [Line Items]
Net investment income (loss)	(346,000)	(70,700)
Realized gains	1,830,800	1,722,300
Net change in unrealized appreciation (depreciation)	3,819,000	1,443,700
Net income	5,303,800	3,095,300
Alternative investments
Schedule of Equity Method Investments [Line Items]
Alternative investment income included in "Net investment income earned" on our Consolidated Statements of Income	$ 6,881	$ 7,768

Investments - Investments Pledg

Investments - Investments Pledged as Collateral (Details) $ in Millions	Mar. 31, 2024 USD ($)
U.S. government and government agencies
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	$ 20
Securities owned and pledged as collateral, fair value	20
Obligations of states and political subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	4.2
Securities owned and pledged as collateral, fair value	4.2
RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	0
Securities owned and pledged as collateral, fair value	90.3
CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	0
Securities owned and pledged as collateral, fair value	10.8
Total pledged as collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	24.2
Securities owned and pledged as collateral, fair value	125.3
Federal Home Loan Bank of Indianapolis | U.S. government and government agencies
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0
Federal Home Loan Bank of Indianapolis | Obligations of states and political subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0
Federal Home Loan Bank of Indianapolis | RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	66.2
Federal Home Loan Bank of Indianapolis | CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	2.3
Federal Home Loan Bank of Indianapolis | Total pledged as collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	68.5
Federal Home Loan Bank of New York | U.S. government and government agencies
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0
Federal Home Loan Bank of New York | Obligations of states and political subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0
Federal Home Loan Bank of New York | RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	24.1
Federal Home Loan Bank of New York | CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	8.5
Federal Home Loan Bank of New York | Total pledged as collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	$ 32.6

Investments - Credit Concentrat

Investments - Credit Concentration Risk (Details)	Mar. 31, 2024	Dec. 31, 2023
Investments [Abstract]
Maximum exposure to credit concentration risk of a single issuer of the Company's stockholder's equity, other than to certain U.S. government-backed investments	10%	10%

Investments - Net Investment In

Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net Investment Income [Line Items]
Net investment income earned	$ 107,849	$ 91,506
Fixed income securities
Net Investment Income [Line Items]
Net investment income earned	94,102	80,087
Commercial mortgage loans ("CMLs")
Net Investment Income [Line Items]
Net investment income earned	2,794	1,965
Equity securities
Net Investment Income [Line Items]
Net investment income earned	4,908	1,205
Short-term investments
Net Investment Income [Line Items]
Net investment income earned	3,519	4,650
Alternative investments
Net Investment Income [Line Items]
Net investment income earned	6,881	7,768
Other investments
Net Investment Income [Line Items]
Net investment income earned	263	43
Investment expenses
Net Investment Income [Line Items]
Investment expenses	$ (4,618)	$ (4,212)

Investments - Net Realized and

Investments - Net Realized and Unrealized Investment Gains and (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Gain (Loss) on Securities [Line Items]
Gross gains on sales	$ 2,135	$ 3,784
Gross losses on sales	(1,965)	(12,930)
Net realized gains (losses) on disposals	170	(9,146)
Net unrealized gains (losses) on equity securities	692	3,248
Losses on securities for which we have the intent to sell	(15)	(304)
Net realized and unrealized investment gains (losses)	(1,635)	3,344
Available-for-Sale Securities
Gain (Loss) on Securities [Line Items]
Net credit loss benefit (expense)	(2,650)	9,529
Commercial mortgage loans ("CMLs")
Gain (Loss) on Securities [Line Items]
Net credit loss benefit (expense)	$ 168	$ 17

Investments - Realized and Unre

Investments - Realized and Unrealized Gains (Losses) on Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Investments [Abstract]
Unrealized gains (losses) recognized in income on equity securities remaining in our portfolio at end of period	$ 692	$ (142)
Unrealized gains (losses) recognized in income on equity securities sold in period	0	3,390
Total unrealized gains (losses) recognized in income on equity securities	$ 692	$ 3,248

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Values and Estimated Fair Values of Financial Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 503,305	$ 503,946
Long-term debt, fair value	497,298	503,805
Finance lease obligations	$ 1,909	2,636
7.25% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	7.25%
Long-term debt, fair value	$ 51,137	53,047
7.25% Senior Notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 49,927	49,926
6.70% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	6.70%
Long-term debt, fair value	$ 101,666	104,039
6.70% Senior Notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 99,571	99,565
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	5.375%
Long-term debt, fair value	$ 286,927	288,787
5.375% Senior Notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 294,548	294,523
3.03% borrowings from FHLBI
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	3.03%
Long-term debt, fair value	$ 57,568	57,932
3.03% borrowings from FHLBI | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	60,000	60,000
Long Term Debt Excluding Issuance Costs and Finance Lease Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	497,298	503,805
Long Term Debt Excluding Issuance Costs and Finance Lease Obligations | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	504,046	504,014
Unamortized Debt Issuance Costs | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized debt issuance costs	$ (2,650)	$ (2,704)

Fair Value Measurements - Quant

Fair Value Measurements - Quantitative Disclosures of Fair Value Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
AFS fixed income securities	$ 7,583,504	$ 7,499,197
Equity securities	194,320	187,155
Short-term investments	247,883	309,317
Fair Value, Recurring
AFS fixed income securities	7,583,504	7,499,197
Equity securities	194,320	187,155
Short-term investments	247,883	309,317
Total assets measured at fair value	8,025,707	7,995,669
U.S. government and government agencies
AFS fixed income securities	141,826	205,035
U.S. government and government agencies | Fair Value, Recurring
AFS fixed income securities	141,826	205,035
Foreign government
AFS fixed income securities	9,229	9,803
Foreign government | Fair Value, Recurring
AFS fixed income securities	9,229	9,803
Obligations of states and political subdivisions
AFS fixed income securities	538,986	585,965
Obligations of states and political subdivisions | Fair Value, Recurring
AFS fixed income securities	538,986	585,965
Corporate securities
AFS fixed income securities	2,795,050	2,711,239
Corporate securities | Fair Value, Recurring
AFS fixed income securities	2,795,050	2,711,239
CLO and other ABS
AFS fixed income securities	1,897,085	1,834,827
CLO and other ABS | Fair Value, Recurring
AFS fixed income securities	1,897,085	1,834,827
RMBS
AFS fixed income securities	1,511,959	1,477,483
RMBS | Fair Value, Recurring
AFS fixed income securities	1,511,959	1,477,483
CMBS
AFS fixed income securities	689,369	674,845
CMBS | Fair Value, Recurring
AFS fixed income securities	689,369	674,845
Common stock: | Fair Value, Recurring
Equity securities	192,510	185,339
Preferred stock | Fair Value, Recurring
Equity securities	1,810	1,816
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Fair Value, Recurring
AFS fixed income securities	33,530	34,056
Equity securities	38,143	22,398
Short-term investments	246,904	308,512
Total assets measured at fair value	318,577	364,966
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | U.S. government and government agencies | Fair Value, Recurring
AFS fixed income securities	33,530	34,056
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Foreign government | Fair Value, Recurring
AFS fixed income securities	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Obligations of states and political subdivisions | Fair Value, Recurring
AFS fixed income securities	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Corporate securities | Fair Value, Recurring
AFS fixed income securities	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | CLO and other ABS | Fair Value, Recurring
AFS fixed income securities	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | RMBS | Fair Value, Recurring
AFS fixed income securities	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | CMBS | Fair Value, Recurring
AFS fixed income securities	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Common stock: | Fair Value, Recurring
Equity securities	36,333	20,582
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Preferred stock | Fair Value, Recurring
Equity securities	1,810	1,816
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring
AFS fixed income securities	6,994,279	6,914,306
Equity securities	0	0
Short-term investments	979	805
Total assets measured at fair value	6,995,258	6,915,111
Significant Other Observable Inputs (Level 2) | U.S. government and government agencies | Fair Value, Recurring
AFS fixed income securities	108,296	170,979
Significant Other Observable Inputs (Level 2) | Foreign government | Fair Value, Recurring
AFS fixed income securities	9,229	9,803
Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions | Fair Value, Recurring
AFS fixed income securities	531,239	578,131
Significant Other Observable Inputs (Level 2) | Corporate securities | Fair Value, Recurring
AFS fixed income securities	2,507,554	2,413,907
Significant Other Observable Inputs (Level 2) | CLO and other ABS | Fair Value, Recurring
AFS fixed income securities	1,636,988	1,589,514
Significant Other Observable Inputs (Level 2) | RMBS | Fair Value, Recurring
AFS fixed income securities	1,511,959	1,477,483
Significant Other Observable Inputs (Level 2) | CMBS | Fair Value, Recurring
AFS fixed income securities	689,014	674,489
Significant Other Observable Inputs (Level 2) | Common stock: | Fair Value, Recurring
Equity securities	0	0
Significant Other Observable Inputs (Level 2) | Preferred stock | Fair Value, Recurring
Equity securities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring
AFS fixed income securities	555,695	550,835
Equity securities	1,067	854
Short-term investments	0	0
Total assets measured at fair value	556,762	551,689
Significant Unobservable Inputs (Level 3) | U.S. government and government agencies | Fair Value, Recurring
AFS fixed income securities	0	0
Significant Unobservable Inputs (Level 3) | Foreign government | Fair Value, Recurring
AFS fixed income securities	0	0
Significant Unobservable Inputs (Level 3) | Obligations of states and political subdivisions | Fair Value, Recurring
AFS fixed income securities	7,747	7,834
Significant Unobservable Inputs (Level 3) | Corporate securities | Fair Value, Recurring
AFS fixed income securities	287,496	297,332
Significant Unobservable Inputs (Level 3) | CLO and other ABS | Fair Value, Recurring
AFS fixed income securities	260,097	245,313
Significant Unobservable Inputs (Level 3) | RMBS | Fair Value, Recurring
AFS fixed income securities	0	0
Significant Unobservable Inputs (Level 3) | CMBS | Fair Value, Recurring
AFS fixed income securities	355	356
Significant Unobservable Inputs (Level 3) | Common stock: | Fair Value, Recurring
Equity securities	1,067	854
Significant Unobservable Inputs (Level 3) | Preferred stock | Fair Value, Recurring
Equity securities	0	0
Fair Value Measured at Net Asset Value Per Share
Equity securities	$ 155,100	$ 163,900

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Fair Value of Securities Using Level 3 Inputs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 551,689
Fair value, ending balance	556,762
Obligations of states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	7,834	$ 6,661
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, ending balance	7,747	6,874
Change in unrealized gains (losses) for the period included in earnings for assets held at period end	(1)	61
Change in unrealized gains (losses) for the period included in OCI for assets held at period end	(86)	152
Obligations of states and political subdivisions | Other Comprehensive Income (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in OCI	(86)	152
Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	297,332	187,980
Purchases	1,152	24,799
Sales	0	0
Issuances	0	0
Settlements	(2,870)	(4,044)
Transfers into Level 3	20,065	361
Transfers out of Level 3	(28,227)	0
Fair value, ending balance	287,496	211,585
Change in unrealized gains (losses) for the period included in earnings for assets held at period end	140	72
Change in unrealized gains (losses) for the period included in OCI for assets held at period end	(376)	2,405
Corporate securities | Other Comprehensive Income (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in OCI	(376)	2,405
CLO and other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	245,313	153,342
Purchases	14,658	13,403
Sales	0	0
Issuances	0	0
Settlements	(1,173)	(1,192)
Transfers into Level 3	19,537	14,148
Transfers out of Level 3	(18,693)	(534)
Fair value, ending balance	260,097	179,758
Change in unrealized gains (losses) for the period included in earnings for assets held at period end	57	(73)
Change in unrealized gains (losses) for the period included in OCI for assets held at period end	399	696
CLO and other ABS | Other Comprehensive Income (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in OCI	399	696
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	356	375
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(3)	(3)
Transfers into Level 3	0	2,848
Transfers out of Level 3	0	0
Fair value, ending balance	355	3,236
Change in unrealized gains (losses) for the period included in earnings for assets held at period end	0	0
Change in unrealized gains (losses) for the period included in OCI for assets held at period end	3	17
CMBS | Other Comprehensive Income (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in OCI	3	17
Common stock:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	854	897
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, ending balance	1,067	628
Change in unrealized gains (losses) for the period included in earnings for assets held at period end	213	(269)
Change in unrealized gains (losses) for the period included in OCI for assets held at period end	0	0
Common stock: | Other Comprehensive Income (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in OCI	0	0
Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	551,689	349,255
Purchases	15,810	38,202
Sales	0	0
Issuances	0	0
Settlements	(4,046)	(5,239)
Transfers into Level 3	39,602	17,357
Transfers out of Level 3	(46,920)	(534)
Fair value, ending balance	556,762	402,081
Change in unrealized gains (losses) for the period included in earnings for assets held at period end	409	(209)
Change in unrealized gains (losses) for the period included in OCI for assets held at period end	(60)	3,270
Investments | Other Comprehensive Income (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in OCI	(60)	3,270
Gain (Loss) on Investments | Obligations of states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	(1)	61
Gain (Loss) on Investments | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	140	72
Gain (Loss) on Investments | CLO and other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	57	(73)
Gain (Loss) on Investments | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	0	0
Gain (Loss) on Investments | Common stock:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	213	(269)
Gain (Loss) on Investments | Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	409	(209)
Net Investment Income Earned | Obligations of states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	0	0
Net Investment Income Earned | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	280	12
Net Investment Income Earned | CLO and other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	(1)	(32)
Net Investment Income Earned | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	(1)	(1)
Net Investment Income Earned | Common stock:
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	0	0
Net Investment Income Earned | Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total net gains (losses) for the period included in net income	$ 278	$ (21)

Fair Value Measurements - Qua_2

Fair Value Measurements - Quantitative Information about Significant Unobservable Inputs in the Fair Value Measurement of Level 3 Assets (Details) $ in Thousands	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investment assets measured at fair value	$ 245,842	$ 288,955
Total Level 3 securities	556,762	551,689
Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Level 3 securities	287,496	297,332	$ 211,585	$ 187,980
CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Level 3 securities	260,097	245,313	$ 179,758	$ 153,342
Valuation Technique, Discounted Cash Flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	310,920	262,734
Valuation Technique, Discounted Cash Flow | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	155,633	135,524
Valuation Technique, Discounted Cash Flow | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 155,287	$ 127,210
Valuation Technique, Discounted Cash Flow | Measurement Input, Credit Spread | Minimum | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	(0.044)	(0.044)
Valuation Technique, Discounted Cash Flow | Measurement Input, Credit Spread | Minimum | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.0001	0.0001
Valuation Technique, Discounted Cash Flow | Measurement Input, Credit Spread | Maximum | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.053	0.053
Valuation Technique, Discounted Cash Flow | Measurement Input, Credit Spread | Maximum | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.196	0.196
Valuation Technique, Discounted Cash Flow | Measurement Input, Credit Spread | Weighted Average | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.018	0.019
Valuation Technique, Discounted Cash Flow | Measurement Input, Credit Spread | Weighted Average | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.024	0.024

Fair Value Measurements - Qua_3

Fair Value Measurements - Quantitative Information of Our Financial Assets and Liabilities That Were Disclosed at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	$ 19,183	$ 21,923
Commercial mortgage loans, fair value	197,807	178,913
Long-term debt, fair value	497,298	503,805
Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	19,183	21,923
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Commercial mortgage loans, fair value	0	0
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) | Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	19,183	21,923
Commercial mortgage loans, fair value	0	0
Long-term debt, fair value	497,298	503,805
Significant Other Observable Inputs (Level 2) | Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	19,183	21,923
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Commercial mortgage loans, fair value	197,807	178,913
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) | Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
7.25% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	51,137	53,047
7.25% Senior Notes | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
7.25% Senior Notes | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	51,137	53,047
7.25% Senior Notes | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
6.70% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	101,666	104,039
6.70% Senior Notes | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
6.70% Senior Notes | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	101,666	104,039
6.70% Senior Notes | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	286,927	288,787
5.375% Senior Notes | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
5.375% Senior Notes | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	286,927	288,787
5.375% Senior Notes | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
3.03% borrowings from FHLBI
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	57,568	57,932
3.03% borrowings from FHLBI | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
3.03% borrowings from FHLBI | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	57,568	57,932
3.03% borrowings from FHLBI | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 0	$ 0

Allowance for Credit Losses o_3

Allowance for Credit Losses on Premiums Receivable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 18,900	$ 16,100
Current period change for expected credit losses	1,784	1,910
Write-offs charged against the allowance for credit losses	(1,056)	(1,164)
Recoveries	372	254
Allowance for credit losses, end of period	$ 20,000	$ 17,100

Reinsurance - Disaggregation of

Reinsurance - Disaggregation of Reinsurance Recoverable by Financial Strength Rating and Aging Analysis (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	$ 653,085	$ 658,525
Less: allowance for credit losses	(1,700)	(1,700)	$ (2,300)	$ (1,600)
Total reinsurance recoverable, net	651,385	656,825
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments, Gross
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	653,085
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments, Gross | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	650,685	654,071
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments, Gross | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	2,400	4,454
Federal and state pools
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	77,799	80,506
Federal and state pools | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	77,799	80,506
Federal and state pools | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	0	0
Other than federal and state pools
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	4,639	4,565
Other than federal and state pools | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	4,135	4,488
Other than federal and state pools | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	504	77
Total non-rated reinsurers
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	82,438	85,071
Total non-rated reinsurers | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	81,934	84,994
Total non-rated reinsurers | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	504	77
A++
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	83,425	82,487
A++ | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	83,372	82,466
A++ | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	53	21
A+
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	367,600	374,019
A+ | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	366,428	371,132
A+ | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	1,172	2,887
A
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	115,668	113,263
A | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	115,086	111,883
A | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	582	1,380
A-
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	3,954	3,685
A- | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	3,865	3,596
A- | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	89	89
Total rated reinsurers
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	570,647	573,454
Total rated reinsurers | Current
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	568,751	569,077
Total rated reinsurers | Past Due
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Total reinsurance recoverable, gross	$ 1,896	$ 4,377

Reinsurance - Allowance for Cre

Reinsurance - Allowance for Credit Losses on Reinsurance Recoverable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 1,700	$ 1,600
Current period change for expected credit losses	0	700
Write-offs charged against the allowance for credit losses	0	0
Recoveries	0	0
Allowance for credit losses, end of period	$ 1,700	$ 2,300

Reinsurance - List of Direct, A

Reinsurance - List of Direct, Assumed, and Ceded Reinsurance Amounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Premiums written:
Direct	$ 1,315,911	$ 1,132,760
Assumed	5,985	5,394
Ceded	(165,275)	(138,386)
Net	1,156,621	999,768
Premiums earned:
Direct	1,205,368	1,032,228
Assumed	6,191	6,290
Ceded	(160,615)	(136,182)
Net	1,050,944	902,336
Loss and loss expense incurred:
Direct	753,567	613,229
Assumed	5,981	5,255
Ceded	(55,256)	(51,046)
Net	$ 704,292	$ 567,438

Reserve for Loss and Loss Exp_3

Reserve for Loss and Loss Expense - Rollforward of Reserve for Loss and Loss Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserve for loss and loss expense, at beginning of period	$ 5,336,911	$ 5,144,821
Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of period	618,601	757,513
Net reserve for loss and loss expense, at beginning of period	4,718,310	4,387,308
Incurred loss and loss expense for claims occurring in the:
Current year	688,519	580,408
Prior years	15,773	(12,970)
Total incurred loss and loss expense	704,292	567,438
Paid loss and loss expense for claims occurring in the:
Current year	107,719	91,011
Prior years	435,489	418,194
Total paid loss and loss expense	543,208	509,205
Net reserve for loss and loss expense, at end of period	4,879,394	4,445,541
Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period	622,356	653,909
Gross reserve for loss and loss expense, at end of period	$ 5,501,750	$ 5,099,450

Reserve for Loss and Loss Exp_4

Reserve for Loss and Loss Expense - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	$ 15,773	$ (12,970)
Casualty reserve
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	35,000
Casualty reserve | Workers' compensation
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year		(10,000)
Casualty reserve | E&S
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year		(5,000)
Casualty reserve | Personal automobile
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year		$ 2,000
Casualty reserve | Standard Commercial Lines | General liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	50,000
Casualty reserve | Standard Commercial Lines | Workers' compensation
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	(15,000)
Casualty reserve | Standard Personal Lines | Homeowners
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	(5,000)
Casualty reserve | Standard Personal Lines | Personal automobile
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	5,000
Property reserve
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred loss and loss expense for claims occurring in the prior year	$ (19,200)

Segment Information - Narrative

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 31, 2024 segment
Segment Reporting [Abstract]
Number of reportable segments	4

Segment Information - Revenue b

Segment Information - Revenue by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net premiums earned:	$ 1,050,944	$ 902,336
Miscellaneous income	7,801	2,634
Net investment income earned	107,849	91,506
Net realized and unrealized investment gains (losses)	(1,635)	3,344
Total Investments revenue	106,214	94,850
Total revenues	1,164,959	999,820
Standard Commercial Lines
Segment Reporting Information [Line Items]
Total revenues	841,244	733,796
Standard Commercial Lines | General liability
Segment Reporting Information [Line Items]
Net premiums earned:	273,415	243,349
Standard Commercial Lines | Commercial automobile
Segment Reporting Information [Line Items]
Net premiums earned:	251,720	217,371
Standard Commercial Lines | Commercial property
Segment Reporting Information [Line Items]
Net premiums earned:	161,553	135,292
Standard Commercial Lines | Workers compensation
Segment Reporting Information [Line Items]
Net premiums earned:	87,777	84,184
Standard Commercial Lines | Businessowners' policies
Segment Reporting Information [Line Items]
Net premiums earned:	39,921	33,171
Standard Commercial Lines | Bonds
Segment Reporting Information [Line Items]
Net premiums earned:	12,088	11,397
Standard Commercial Lines | Other
Segment Reporting Information [Line Items]
Net premiums earned:	7,636	6,851
Standard Commercial Lines | Miscellaneous income
Segment Reporting Information [Line Items]
Miscellaneous income	7,134	2,181
Standard Personal Lines
Segment Reporting Information [Line Items]
Total revenues	104,486	82,323
Standard Personal Lines | Miscellaneous income
Segment Reporting Information [Line Items]
Miscellaneous income	640	453
Standard Personal Lines | Personal automobile
Segment Reporting Information [Line Items]
Net premiums earned:	56,960	44,914
Standard Personal Lines | Homeowners
Segment Reporting Information [Line Items]
Net premiums earned:	44,113	35,013
Standard Personal Lines | Other
Segment Reporting Information [Line Items]
Net premiums earned:	2,773	1,943
E&S Lines
Segment Reporting Information [Line Items]
Total revenues	113,015	88,851
E&S Lines | Miscellaneous income
Segment Reporting Information [Line Items]
Miscellaneous income	27	0
E&S Lines | Casualty lines
Segment Reporting Information [Line Items]
Net premiums earned:	71,638	60,817
E&S Lines | Property lines
Segment Reporting Information [Line Items]
Net premiums earned:	$ 41,350	$ 28,034

Segment Information - Income Be

Segment Information - Income Before and After Federal Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net investment income earned	$ 107,849	$ 91,506
Net realized and unrealized investment gains (losses)	(1,635)	3,344
Total investments segment income, before federal income tax	106,214	94,850
Tax on investments segment income	21,866	19,156
Total investments segment income, after federal income tax	84,348	75,694
Standard Commercial Lines
Segment Reporting Information [Line Items]
Underwriting income (loss), before federal income tax	10,381	38,921
Underwriting income (loss), after federal income tax	$ 8,201	$ 30,748
Combined ratio	98.80%	94.70%
ROE contribution	1.20%	5.10%
Standard Personal Lines
Segment Reporting Information [Line Items]
Underwriting income (loss), before federal income tax	$ (5,335)	$ (13,073)
Underwriting income (loss), after federal income tax	$ (4,215)	$ (10,328)
Combined ratio	105.10%	116%
ROE contribution	(0.60%)	(1.70%)
E&S Lines
Segment Reporting Information [Line Items]
Underwriting income (loss), before federal income tax	$ 13,985	$ 13,335
Underwriting income (loss), after federal income tax	$ 11,048	$ 10,535
Combined ratio	87.60%	85%
ROE contribution	1.60%	1.80%
Investments:
Segment Reporting Information [Line Items]
ROE contribution	12.30%	12.20%
Total investments segment income, before federal income tax	$ 106,214	$ 94,850

Segment Information - Reconcili

Segment Information - Reconciliation of Segment Results to Income Before Federal Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investment income	$ 106,214	$ 94,850
Interest expense	(7,181)	(7,166)
Corporate expenses	(15,498)	(12,108)
Income, before federal income tax	102,566	114,759
Preferred stock dividends	(2,300)	(2,300)
Income available to common stockholders, before federal income tax	100,266	112,459
Standard Commercial Lines
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting income (loss)	10,381	38,921
Standard Personal Lines
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting income (loss)	(5,335)	(13,073)
E&S Lines
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting income (loss)	13,985	13,335
Investments:
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investment income	106,214	94,850
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total all segments	$ 125,245	$ 134,033

Retirement Plans - Components o

Retirement Plans - Components of Net Periodic Benefit Cost (Details) - Defined benefit pension and post-retirement life plans - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Interest cost	$ 3,888	$ 3,866
Expected return on plan assets	(5,382)	(5,773)
Amortization of unrecognized net actuarial loss	955	751
Total net periodic pension cost (benefit)	$ (539)	$ (1,156)

Retirement Plans - Weighted-Ave

Retirement Plans - Weighted-Average Expense Assumptions (Details) - Defined benefit pension and post-retirement life plans	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	5.02%	5.21%
Effective interest rate for calculation of interest cost	4.91%	5.09%
Expected return on plan assets	6.40%	6.90%

Comprehensive Income - Componen

Comprehensive Income - Components of Comprehensive Income-Gross and Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income, Gross	$ 102,566	$ 114,759
Unrealized holding gains (losses) during the period, Gross	(15,560)	65,925
Unrealized gains (losses) on securities with credit loss recognized in earnings, Gross	(3,132)	22,431
Amounts reclassified into net income: net realized (gains) losses on disposals and intent-to-sell AFS securities, Gross	(78)	6,104
Amounts reclassified into net income: Credit loss (benefit) expense, Gross	2,650	(9,529)
Total unrealized gains (losses) on investment securities, Gross	(16,120)	84,931
Amount reclassified into net income: Net actuarial (gain) loss, Gross	967	757
Total defined benefit pension and post-retirement plans, Gross	967	757
Other comprehensive income (loss), Gross	(15,153)	85,688
Comprehensive income (loss), Gross	87,413	200,447
Net income, Tax	20,048	22,185
Unrealized holding gains (losses) during the period, Tax	(3,267)	13,846
Unrealized gains (losses) on securities with credit loss recognized in earnings, Tax	(658)	4,710
Amounts reclassified into net income: net realized (gains) losses on disposals and intent-to-sell AFS securities, Tax	(17)	1,282
Amounts reclassified into net income: Credit loss (benefit) expense, Tax	557	(2,002)
Total unrealized gains (losses) on investment securities, Tax	(3,385)	17,836
Amount reclassified into net income: Net actuarial (gain) loss, Tax	203	159
Total defined benefit pension and post-retirement plans, Tax	203	159
Other comprehensive income (loss), Tax	(3,182)	17,995
Comprehensive income (loss), Tax	16,866	40,180
Net income	82,518	92,574
Unrealized holding gains (losses) during the period, Net	(12,293)	52,079
Unrealized gains (losses) on securities with credit loss recognized in earnings, Net	(2,474)	17,721
Amounts reclassified into net income: net realized (gains) losses on disposals and intent-to-sell AFS securities, Net	(61)	4,822
Amounts reclassified into net income: Credit loss (benefit) expense, Net	2,093	(7,527)
Total unrealized gains (losses) on investment securities	(12,735)	67,095
Amount reclassified into net income: Net actuarial (gain) loss, Net	764	598
Total defined benefit pension and post-retirement plans	764	598
Other comprehensive income (loss)	(11,971)	67,693
Comprehensive income (loss)	$ 70,547	$ 160,267

Comprehensive Income - Compon_2

Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	$ (373,001)
Net current period OCI	(11,971)	$ 67,693
Ending Balance, March 31, 2024	(384,972)
Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(194,628)
OCI before reclassifications	(12,293)
Amounts reclassified from AOCI	(61)
Net current period OCI	(12,354)
Ending Balance, March 31, 2024	(206,982)
Investments Subtotal
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(279,070)
OCI before reclassifications	(14,767)
Amounts reclassified from AOCI	2,032
Net current period OCI	(12,735)
Ending Balance, March 31, 2024	(291,805)
Credit Loss Related
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(84,442)
OCI before reclassifications	(2,474)
Amounts reclassified from AOCI	2,093
Net current period OCI	(381)
Ending Balance, March 31, 2024	(84,823)
Defined benefit pension and post-retirement life plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(93,931)
OCI before reclassifications	0
Amounts reclassified from AOCI	764
Net current period OCI	764
Ending Balance, March 31, 2024	(93,167)
Total AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(373,001)
OCI before reclassifications	(14,767)
Amounts reclassified from AOCI	2,796
Net current period OCI	(11,971)	$ 67,693
Ending Balance, March 31, 2024	$ (384,972)

Comprehensive Income - Reclassi

Comprehensive Income - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net realized and unrealized investment gains (losses)	$ (1,635)	$ 3,344
Total federal income tax expense	(20,048)	(22,185)
Loss and loss expense incurred	704,292	567,438
Other insurance expenses	115,987	108,588
Income, before federal income tax	102,566	114,759
Net income	82,518	92,574
Reclassification out of AOCI
Net income	2,796	(2,107)
Reclassification out of AOCI | Defined benefit pension and post-retirement life plans
Total federal income tax expense	(203)	(159)
Loss and loss expense incurred	222	175
Other insurance expenses	745	582
Income, before federal income tax	967	757
Net income	764	598
Reclassification out of AOCI | Net realized (gains) losses on disposals and intent-to-sell AFS securities
Net realized and unrealized investment gains (losses)	(78)	6,104
Total federal income tax expense	17	(1,282)
Net income	(61)	4,822
Reclassification out of AOCI | Credit loss related
Net realized and unrealized investment gains (losses)	2,650	(9,529)
Total federal income tax expense	(557)	2,002
Net income	$ 2,093	$ (7,527)

Earnings per Common Share (Deta

Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Net income available to common stockholders:	$ 80,218	$ 90,274
Weighted average common shares outstanding - basic (in shares)	60,827	60,536
Effect of dilutive securities - stock compensation plans (in shares)	386	372
Weighted average common shares outstanding - diluted (in shares)	61,213	60,908
Earnings per share - Basic (in dollars per share)	$ 1.32	$ 1.49
Earnings per share - Diluted (in dollars per share)	$ 1.31	$ 1.48

Litigation (Details)

Litigation (Details)	Mar. 31, 2024 subsidiary
Commitments and Contingencies Disclosure [Abstract]
Number of insurance subsidiaries	10