RLI (RLI) 10-Q 24 Jul 24 2024 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2024	Jul. 16, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2024
Entity File Number	001-09463
Entity Registrant Name	RLI Corp
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	37-0889946
Entity Address, Address Line One	9025 North Lindbergh Drive,
Entity Address, City or Town	Peoria,
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	61615
City Area Code	309
Local Phone Number	692-1000
Title of 12(b) Security	Common Stock $0.01 par value
Trading Symbol	RLI
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		45,746,054
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Entity Central Index Key	0000084246
Amendment Flag	false

Condensed Consolidated Statemen

Condensed Consolidated Statements of Earnings and Comprehensive Earnings - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Statement [Abstract]
Net premiums earned	$ 379,065	$ 322,280	$ 739,741	$ 630,003
Net investment income	33,961	28,788	66,808	55,872
Net realized gains (losses)	(192)	5,580	5,802	20,200
Net unrealized gains on equity securities	3,608	25,214	48,922	40,710
Consolidated revenue	416,442	381,862	861,273	746,785
Losses and settlement expenses	167,799	153,943	311,623	268,431
Policy acquisition costs	113,921	102,626	224,375	204,070
Insurance operating expenses	27,321	24,510	56,024	48,411
Interest expense on debt	1,604	2,047	3,222	4,055
General corporate expenses	4,140	4,219	9,150	8,433
Total expenses	314,785	287,345	604,394	533,400
Equity in earnings of unconsolidated investees	1,646	1,514	6,415	5,437
Earnings (loss) before income taxes	103,303	96,031	263,294	218,822
Income tax expense	21,311	18,379	53,402	42,359
Net earnings (loss)	81,992	77,652	209,892	176,463
Other comprehensive earnings (loss), net of tax	(7,843)	(19,721)	(20,514)	17,986
Comprehensive earnings	$ 74,149	$ 57,931	$ 189,378	$ 194,449
Basic net earnings per share	$ 1.79	$ 1.70	$ 4.59	$ 3.87
Diluted net earnings per share	$ 1.78	$ 1.69	$ 4.55	$ 3.83
Weighted average number of common shares outstanding:
Basic	45,737	45,591	45,709	45,560
Diluted	46,179	46,044	46,169	46,045

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
ASSETS
Available-for-sale, at fair value (amortized cost of $3,217,866 and allowance for credit losses of $228 at 6/30/24) (amortized cost of $3,054,391 and allowance for credit losses of $306 at 12/31/23)	$ 2,989,527	$ 2,855,849
Equity securities, at fair value (cost - $381,138 at 6/30/24 and $354,022 at 12/31/23)	666,563	590,041
Short-term investments, at cost which approximates fair value	125,865	134,923
Other invested assets	55,364	59,081
Cash	50,030	36,424
Total investments and cash	3,887,349	3,676,318
Accrued investment income	26,683	24,062
Premiums and reinsurance balances receivable, net of allowances for uncollectible amounts of $21,791 at 6/30/24 and $21,438 at 12/31/23	294,774	221,206
Ceded unearned premium	114,893	112,257
Reinsurance balances recoverable on unpaid losses and settlement expenses, net of allowances for uncollectible amounts of $11,025 at 6/30/24 and $10,608 at 12/31/23	782,288	757,349
Deferred policy acquisition costs	167,295	146,566
Property and equipment, at cost, net of accumulated depreciation of $74,768 at 6/30/24 and $74,279 at 12/31/23	46,574	46,715
Investment in unconsolidated investees	67,249	56,966
Goodwill and intangibles	53,562	53,562
Income taxes-deferred	12,291	15,872
Other assets	58,715	69,348
TOTAL ASSETS	5,511,673	5,180,221
Liabilities
Unpaid loss and settlement expenses	2,544,622	2,446,025
Unearned premiums	992,754	892,326
Reinsurance balances payable	38,968	71,507
Funds held	107,235	101,446
Income taxes-current	7,610	3,757
Debt	100,000	100,000
Accrued expenses	83,805	108,880
Other liabilities	51,972	42,766
TOTAL LIABILITIES	3,926,966	3,766,707
Shareholders' Equity
Common stock ($0.01 par value) (Shares authorized - 200,000,000) (68,676,268 shares issued, 45,746,054 shares outstanding at 6/30/24) (68,570,261 shares issued, 45,640,047 shares outstanding at 12/31/23)	687	686
Paid-in capital	369,785	362,345
Accumulated other comprehensive earnings (loss)	(186,817)	(166,303)
Retained earnings	1,794,051	1,609,785
Deferred compensation	13,183	13,539
Treasury shares, at cost (22,930,214 shares at 6/30/24 and 12/31/23)	(406,182)	(406,538)
TOTAL SHAREHOLDERS' EQUITY	1,584,707	1,413,514
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 5,511,673	$ 5,180,221

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Statement Of Financial Position [Abstract]
Available-for-sale, amortized cost	$ 3,217,866	$ 3,054,391
Available-for-sale, allowance for credit losses	228	306
Equity securities, cost	381,138	354,022
Premiums and reinsurance balances receivable, allowances for uncollectible amounts	21,791	21,438
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	11,025	10,608
Property and equipment, accumulated depreciation	$ 74,768	$ 74,279
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	68,676,268	68,570,261
Common stock, shares outstanding (in shares)	45,746,054	45,640,047
Treasury stock, shares (in shares)	22,930,214	22,930,214

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common stock	Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Deferred Compensation	Treasury Stock at Cost	Cumulative Effect, Period of Adoption, Adjustment	Total
Shareholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2022	$ 684	$ 352,391	$ (229,076)	$ (951)	$ 1,446,341	$ 12,015	$ (405,014)	$ (951)	$ 1,177,341
Shares, Outstanding, Beginning Balance at Dec. 31, 2022	45,469,752
Increase Decrease In Shareholders Equity Roll Forward
Net Income (Loss)					98,811				98,811
Other comprehensive earnings (loss), net of tax			37,707						37,707
Deferred compensation						249	(249)
Share-based compensation	$ 1	2,863							2,864
Share-based compensation (in shares)	84,944
Dividends and dividend equivalents					(11,851)				(11,851)
Shareholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2023	$ 685	355,254	(191,369)		1,532,350	12,264	(405,263)		1,303,921
Shares, Outstanding, Ending Balance at Mar. 31, 2023	45,554,696
Shareholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2022	$ 684	352,391	(229,076)	$ (951)	1,446,341	12,015	(405,014)	$ (951)	1,177,341
Shares, Outstanding, Beginning Balance at Dec. 31, 2022	45,469,752
Increase Decrease In Shareholders Equity Roll Forward
Net Income (Loss)									176,463
Other comprehensive earnings (loss), net of tax									17,986
Shareholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2023	$ 685	357,656	(211,090)		1,597,660	12,507	(405,506)		1,351,912
Shares, Outstanding, Ending Balance at Jun. 30, 2023	45,596,196
Shareholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2023	$ 685	355,254	(191,369)		1,532,350	12,264	(405,263)		1,303,921
Shares, Outstanding, Beginning Balance at Mar. 31, 2023	45,554,696
Increase Decrease In Shareholders Equity Roll Forward
Net Income (Loss)					77,652				77,652
Other comprehensive earnings (loss), net of tax			(19,721)						(19,721)
Deferred compensation						243	(243)
Share-based compensation		2,402							2,402
Share-based compensation (in shares)	41,500
Dividends and dividend equivalents					(12,342)				(12,342)
Shareholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2023	$ 685	357,656	(211,090)		1,597,660	12,507	(405,506)		1,351,912
Shares, Outstanding, Ending Balance at Jun. 30, 2023	45,596,196
Shareholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2023	$ 686	362,345	(166,303)		1,609,785	13,539	(406,538)		1,413,514
Shares, Outstanding, Beginning Balance at Dec. 31, 2023	45,640,047
Increase Decrease In Shareholders Equity Roll Forward
Net Income (Loss)					127,900				127,900
Other comprehensive earnings (loss), net of tax			(12,671)						(12,671)
Deferred compensation						(790)	790
Share-based compensation	$ 1	4,356							4,357
Share-based compensation (in shares)	69,834
Dividends and dividend equivalents					(12,348)				(12,348)
Shareholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2024	$ 687	366,701	(178,974)		1,725,337	12,749	(405,748)		1,520,752
Shares, Outstanding, Ending Balance at Mar. 31, 2024	45,709,881
Shareholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2023	$ 686	362,345	(166,303)		1,609,785	13,539	(406,538)		1,413,514
Shares, Outstanding, Beginning Balance at Dec. 31, 2023	45,640,047
Increase Decrease In Shareholders Equity Roll Forward
Net Income (Loss)									209,892
Other comprehensive earnings (loss), net of tax									(20,514)
Shareholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2024	$ 687	369,785	(186,817)		1,794,051	13,183	(406,182)		1,584,707
Shares, Outstanding, Ending Balance at Jun. 30, 2024	45,746,054
Shareholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2024	$ 687	366,701	(178,974)		1,725,337	12,749	(405,748)		1,520,752
Shares, Outstanding, Beginning Balance at Mar. 31, 2024	45,709,881
Increase Decrease In Shareholders Equity Roll Forward
Net Income (Loss)					81,992				81,992
Other comprehensive earnings (loss), net of tax			(7,843)						(7,843)
Deferred compensation						434	(434)
Share-based compensation		3,084							3,084
Share-based compensation (in shares)	36,173
Dividends and dividend equivalents					(13,278)				(13,278)
Shareholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2024	$ 687	$ 369,785	$ (186,817)		$ 1,794,051	$ 13,183	$ (406,182)		$ 1,584,707
Shares, Outstanding, Ending Balance at Jun. 30, 2024	45,746,054

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023
Statement Of Shareholders Equity [Abstract]
Cash dividends paid per common share	$ 0.29	$ 0.27	$ 0.27	$ 0.26

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Statement Of Cash Flows [Abstract]
Net cash provided by operating activities	$ 212,771	$ 243,595
Purchase of:
Fixed income securities, available-for-sale	(369,888)	(365,976)
Equity securities	(45,585)	(25,454)
Property and equipment	(3,840)	(2,790)
Other	(3,591)	(2,669)
Proceeds from sale of:
Fixed income securities - available-for-sale	41,543	19,490
Equity securities	31,473	22,029
Equity method investments		14,134
Other	3,952	473
Proceeds from call or maturity of:
Fixed income securities - available-for-sale	159,869	349,714
Net proceeds from sale (purchase) of short-term investments	9,058	(235,067)
Net cash used in investing activities	(177,009)	(226,116)
Cash Flows from Financing Activities
Cash dividends paid	(25,604)	(24,172)
Proceeds from stock option exercises	3,448	582
Net cash used in financing activities	(22,156)	(23,590)
Net increase (decrease) in cash	13,606	(6,111)
Cash at the beginning of the period	36,424	22,818
Cash at June 30	$ 50,030	$ 16,707

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	NOTES TO UNAUDITED CONDENSED CONSOLIDATED FINANCIAL STATEMENTS ​ 1. BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES ​ A. BASIS OF PRESENTATION ​ The unaudited interim condensed consolidated financial statements of RLI Corp. (the Company) and subsidiaries have been prepared in accordance with generally accepted accounting principles in the United States of America (GAAP). These condensed consolidated financial statements do not include all the disclosures required by GAAP for annual financial statements and should be read in conjunction with our 2023 Annual Report on Form 10-K. In the opinion of the Company’s management, the condensed consolidated financial statements reflect all adjustments, of a normal and recurring nature, that are necessary for fair financial statement presentation. The results of operations for any interim period are not necessarily indicative of the operating results for a full year. ​ The preparation of the unaudited condensed consolidated financial statements requires management to make estimates and assumptions relating to the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of revenue and expenses during the period. These estimates are inherently subject to change and actual results could differ significantly from these estimates. ​ B. ADOPTED ACCOUNTING STANDARDS ​ No new accounting standards applicable in 2024 materially impact our financial statements. ​ C. PROSPECTIVE ACCOUNTING STANDARDS ​ 2023-07—Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures ​ The guidance in ASU 2023-07 was designed to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. This ASU is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Although the Company continues to evaluate the impact of adopting this new accounting standard, the amendments are disclosure-related and should not have a material impact on our financial statements. ​ 2023-09—Income Taxes (Topic 740): Improvements to Income Tax Disclosures ​ The guidance in ASU 2023-09 was designed to increase transparency about income tax information through improvements to the rate reconciliation and disclosure of income taxes paid. This ASU is effective for fiscal years beginning after December 15, 2024. Although the Company continues to evaluate the impact of adopting this new accounting standard, the amendments are disclosure-related and should not have a material impact on our financial statements. ​ D. REINSURANCE ​ Ceded unearned premiums and reinsurance balances recoverable on unpaid losses and settlement expenses are reported separately as an asset, rather than being netted with the related liability, since reinsurance does not relieve the Company of our liability to policyholders. Such balances are subject to the credit risk associated with the individual reinsurer. We continually monitor the financial condition of our reinsurers and actively follow up on any past due or disputed amounts. As part of our monitoring efforts, we review reinsurers’ annual financial statements and Securities and Exchange Commission filings for those that are publicly traded. We also review insurance industry developments that may impact the financial condition of our reinsurers. We analyze the credit risk associated with our reinsurance balances recoverable by monitoring the AM Best and Standard & Poor’s (S&P) ratings of our reinsurers. We subject our reinsurance balances recoverable to detailed recoverability tests, including a segment-based analysis using the average default rating percentage by S&P rating, which assists the Company in assessing the sufficiency of its allowance. Additionally, we perform an in-depth reinsurer financial condition analysis prior to the renewal of our reinsurance placements. ​ Our policy is to charge to earnings, in the form of an allowance, an estimate of unrecoverable amounts from reinsurers. This allowance is reviewed on an ongoing basis to ensure that the amount makes a reasonable provision for reinsurance balances that we may be unable to recover. Once regulatory action (such as receivership, finding of insolvency, order of conservation or order of liquidation) is taken against a reinsurer, the paid and unpaid recoverable balances for the reinsurer are specifically identified and written off through the use of our allowance for estimated unrecoverable amounts from reinsurers. When we write-off such a balance, it is done in full. We then re-evaluate the overall allowance and determine whether the balance is sufficient and, if needed, an additional allowance is recognized. ​ The allowances for uncollectible amounts on paid and unpaid reinsurance balances recoverable were $16 million and $11 million, respectively, at June 30, 2024 and December 31, 2023. Changes in the allowances were due to changes in the amount of reinsurance balances outstanding, the composition of reinsurers from whom the balances were recoverable and their associated S&P default ratings. No write-offs were applied to the allowances in the first six months of 2024 and less than $1 million was recovered. ​ E. INTANGIBLE ASSETS ​ The composition of goodwill and intangible assets at June 30, 2024 and December 31, 2023 is detailed in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (in thousands) 2024 2023 Goodwill ​ ​ ​ ​ ​ ​ Surety ​ $ 40,816 ​ $ 40,816 Casualty ​ ​ 5,246 ​ ​ 5,246 Total goodwill ​ $ 46,062 ​ $ 46,062 Indefinite-lived intangibles ​ ​ 7,500 ​ ​ 7,500 Total goodwill and intangibles ​ $ 53,562 ​ $ 53,562 ​ Annual impairment assessments were performed on our goodwill and state insurance license indefinite-lived intangible assets during the second quarter of 2024. Based upon these reviews, none of the assets were impaired. In addition, there were no triggering events as of June 30, 2024 that would suggest an updated impairment test would be needed for our goodwill and intangible assets. ​ F. EARNINGS PER SHARE ​ Basic earnings per share (EPS) is computed by dividing income available to common shareholders by the weighted-average number of common shares outstanding for the period. Diluted EPS reflects the dilution that could occur if securities or other contracts to issue common stock or common stock equivalents were exercised or converted into common stock. When inclusion of these items increases the earnings per share or reduces the loss per share, the effect on earnings is anti-dilutive. Under these circumstances, the diluted net earnings or net loss per share is computed excluding these items. The following represents a reconciliation of the numerator and denominator of the basic and diluted EPS computations contained in the unaudited condensed consolidated financial statements: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Three Months ​ ​ Ended June 30, 2024 ​ Ended June 30, 2023 ​ ​ Income ​ Shares ​ Per Share ​ Income ​ Shares ​ Per Share (in thousands, except per share data) (Numerator) (Denominator) Amount (Numerator) (Denominator) Amount Basic EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 81,992 ​ 45,737 ​ $ 1.79 ​ $ 77,652 ​ 45,591 ​ $ 1.70 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 442 ​ ​ ​ ​ ​ — ​ 453 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 81,992 ​ 46,179 ​ $ 1.78 ​ $ 77,652 ​ 46,044 ​ $ 1.69 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ For the Six Months ​ ​ Ended June 30, 2024 ​ Ended June 30, 2023 ​ ​ Income ​ Shares ​ Per Share ​ Income ​ Shares ​ Per Share (in thousands, except per share data) (Numerator) (Denominator) Amount (Numerator) (Denominator) Amount Basic EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 209,892 ​ 45,709 ​ $ 4.59 ​ $ 176,463 ​ 45,560 ​ $ 3.87 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 460 ​ ​ ​ ​ ​ — ​ 485 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 209,892 ​ 46,169 ​ $ 4.55 ​ $ 176,463 ​ 46,045 ​ $ 3.83 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 114 ​ ​ ​ ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ G. COMPREHENSIVE EARNINGS ​ Our comprehensive earnings include net earnings plus after-tax unrealized gains and losses on our available-for-sale fixed income portfolio. In reporting the components of comprehensive earnings, we used the federal statutory tax rate of 21 percent. Other comprehensive earnings (loss), as shown in the consolidated statements of earnings and comprehensive earnings, is net of tax benefit of $2 million for the second quarter of 2024, compared to $5 million of tax benefit for the same period in 2023. For the six-month period ended June 30, 2024, other comprehensive earnings (loss) is net of tax benefit of $5 million, compared to $5 million of tax expense for the same period in 2023. ​ Unrealized losses, net of tax, recognized in other comprehensive earnings (loss) were $21 million for the first six months of 2024, compared to $18 million of unrealized gains, net of tax, during the same period last year. The unrealized losses in 2024 were attributable to an increase in interest rates, which decreased the fair value of securities held in the fixed income portfolio. During 2023, modestly tighter credit spreads on relatively steady interest rates increased the fair value of securities held in the fixed income portfolio. ​ The following table illustrates the changes in the balance of each component of accumulated other comprehensive earnings (loss) for each period presented in the unaudited condensed consolidated financial statements: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ For the Three Months ​ For the Six Months ​ ​ Ended June 30, ​ Ended June 30, Unrealized Gains/Losses on Available-for-Sale Securities 2024 2023 2024 2023 Beginning balance ​ $ (178,974) ​ $ (191,369) ​ $ (166,303) ​ $ (229,076) Other comprehensive earnings (loss) before reclassifications ​ ​ (8,571) ​ ​ (20,347) ​ ​ (21,846) ​ ​ 15,908 Amounts reclassified from accumulated other comprehensive earnings ​ ​ 728 ​ ​ 626 ​ ​ 1,332 ​ ​ 2,078 Net current-period other comprehensive earnings (loss) ​ $ (7,843) ​ $ (19,721) ​ $ (20,514) ​ $ 17,986 Ending balance ​ $ (186,817) ​ $ (211,090) ​ $ (186,817) ​ $ (211,090) Balance of securities for which an allowance for credit losses has been recognized in net earnings ​ ​ ​ ​ ​ ​ ​ $ 1,463 ​ $ 1,053 ​ Credit losses on or the sale of an available-for-sale security results in amounts being reclassified from accumulated other comprehensive earnings (loss) to current period net earnings. The effects of reclassifications out of accumulated other comprehensive earnings (loss) by the respective line items of net earnings are presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amount Reclassified from Accumulated Other ​ ​ ​ (in thousands) ​ Comprehensive Earnings (Loss) ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months ​ ​ ​ Component of Accumulated ​ Ended June 30, ​ Ended June 30, ​ ​ Affected line item in the Other Comprehensive Earnings (Loss) 2024 2023 2024 2023 Statement of Earnings Unrealized gains and losses on available-for-sale securities ​ $ (931) ​ $ (824) ​ $ (1,765) ​ $ (2,536) ​ ​ Net realized gains (losses) ​ ​ ​ 9 ​ ​ 31 ​ ​ 79 ​ ​ (95) ​ ​ Credit gains (losses) presented within net realized gains ​ ​ $ (922) ​ $ (793) ​ $ (1,686) ​ $ (2,631) ​ ​ Earnings (loss) before income taxes ​ ​ ​ 194 ​ ​ 167 ​ ​ 354 ​ ​ 553 ​ ​ Income tax (expense) benefit ​ ​ $ (728) ​ $ (626) ​ $ (1,332) ​ $ (2,078) ​ ​ Net earnings (loss) ​ H. FAIR VALUE MEASUREMENTS ​ Fair value is defined as the price in the principal market that would be received for an asset to facilitate an orderly transaction between market participants on the measurement date. We determined the fair value of certain financial instruments based on their underlying characteristics and relevant transactions in the marketplace. We maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. ​ The following are the levels of the fair value hierarchy and a brief description of the type of valuation inputs that are used to establish each level. Financial assets are classified based upon the lowest level of significant input that is used to determine fair value. ​ Level 1 ​ Level 2 ​ Level 3 ​ As a part of management’s process to determine fair value, we utilize widely recognized, third-party pricing sources to determine our fair values. We have obtained an understanding of the third-party pricing sources’ valuation methodologies and inputs. The following is a description of the valuation techniques used for financial assets that are measured at fair value, including the general classification of such assets pursuant to the fair value hierarchy. ​ Corporate, Agencies, Government and Municipal Bonds: ​ Mortgage-backed Securities (MBS)/Commercial Mortgage-backed Securities (CMBS) and Asset-backed Securities (ABS): ​ Regulation D Private Placement Securities: observable and unobservable inputs. Observable inputs include public corporate spread matrices classified by sector, rating and average life, as well as investment and non-investment grade matrices created from fixed income indices. Unobservable inputs include a liquidity spread premium calculated based on public corporate spread and private corporate spread matrices. The quantitative detail of the liquidity spread premium is neither provided nor reasonably available to the Company. An increase to the credit spread assumptions would result in a lower fair value. ​ For all of our fixed income securities classified as Level 2, we periodically conduct a review to assess the reasonableness of the fair values provided by our pricing services. Our review consists of a two-pronged approach. First, we compare prices provided by our pricing services to those provided by an additional source. In some cases, we obtain prices from securities brokers and compare them to the prices provided by our pricing services. If discrepancies are found in our comparisons, we compare our prices to actual reported trade data for like securities. No changes to the fair values supplied by our pricing services have occurred as a result of our reviews. Based on these assessments, we have determined that the fair values of our Level 2 fixed income securities provided by our pricing services are reasonable. ​ Equity Securities: ​ Due to the relatively short-term nature of cash, short-term investments, accounts receivable and accounts payable, their carrying amounts are reasonable estimates of fair value. Our investments in private funds, classified as other invested assets, are measured using the investments’ net asset value per share and are not categorized within the fair value hierarchy. ​

Investments

Investments	6 Months Ended
	Jun. 30, 2024
Investments Debt And Equity Securities [Abstract]
Investments	2. INVESTMENTS ​ Our investments are primarily composed of fixed income debt securities and common stock equity securities. We carry our equity securities at fair value and categorize all of our debt securities as available-for-sale, which are carried at fair value. ​ Realized gains and losses on disposition of investments are based on the specific identification of the investments sold on the settlement date. The following is a summary of the disposition of fixed income and equity securities for the six-month periods ended June 30, 2024 and 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Sales ​ Proceeds ​ Gross Realized ​ Net Realized (in thousands) From Sales Gains Losses Gain (Loss) 2024 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 41,543 ​ $ 357 ​ $ (1,139) ​ $ (782) Equity securities ​ ​ 31,473 ​ ​ 13,344 ​ ​ (340) ​ ​ 13,004 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 20,729 ​ $ 99 ​ $ (910) ​ $ (811) Equity securities ​ ​ 22,029 ​ ​ 8,841 ​ ​ (101) ​ ​ 8,740 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Calls/Maturities ​ ​ ​ ​ Gross Realized ​ Net Realized (in thousands) Proceeds Gains Losses Gain (Loss) 2024 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 158,472 ​ $ 79 ​ $ (856) ​ $ (777) 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 349,734 ​ $ 37 ​ $ (43) ​ $ (6) ​ FAIR VALUE MEASUREMENTS ​ Assets measured at fair value on a recurring basis as of June 30, 2024 and December 31, 2023 are summarized below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of June 30, 2024 ​ ​ Quoted Prices in ​ Significant Other ​ Significant ​ ​ ​ ​ ​ Active Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ ​ ​ (in thousands) (Level 1) (Level 2) (Level 3) Total Fixed income securities - available-for-sale ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. government ​ $ — ​ $ 434,800 ​ $ — ​ $ 434,800 U.S. agency ​ ​ — ​ ​ 58,309 ​ ​ — ​ ​ 58,309 Non-U.S. government & agency ​ ​ — ​ ​ 3,828 ​ ​ — ​ ​ 3,828 Agency MBS ​ ​ — ​ ​ 414,675 ​ ​ — ​ ​ 414,675 ABS/CMBS/MBS* ​ ​ — ​ ​ 320,061 ​ ​ — ​ ​ 320,061 Corporate ​ ​ — ​ ​ 1,182,685 ​ ​ 68,095 ​ ​ 1,250,780 Municipal ​ ​ — ​ ​ 507,074 ​ ​ — ​ ​ 507,074 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,921,432 ​ $ 68,095 ​ $ 2,989,527 Equity securities ​ ​ 661,978 ​ ​ — ​ ​ 4,585 ​ ​ 666,563 Total ​ $ 661,978 ​ $ 2,921,432 ​ $ 72,680 ​ $ 3,656,090 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2023 ​ ​ Quoted Prices in ​ Significant Other ​ Significant ​ ​ ​ ​ ​ Active Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ ​ ​ (in thousands) (Level 1) (Level 2) (Level 3) Total Fixed income securities - available-for-sale ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. government ​ $ — ​ $ 308,031 ​ $ — ​ $ 308,031 U.S. agency ​ ​ — ​ ​ 59,826 ​ ​ — ​ ​ 59,826 Non-U.S. government & agency ​ ​ — ​ ​ 3,882 ​ ​ — ​ ​ 3,882 Agency MBS ​ ​ — ​ ​ 425,285 ​ ​ — ​ ​ 425,285 ABS/CMBS/MBS* ​ ​ — ​ ​ 281,182 ​ ​ — ​ ​ 281,182 Corporate ​ ​ — ​ ​ 1,164,548 ​ ​ 60,471 ​ ​ 1,225,019 Municipal ​ ​ — ​ ​ 552,624 ​ ​ — ​ ​ 552,624 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,795,378 ​ $ 60,471 ​ $ 2,855,849 Equity securities ​ ​ 588,416 ​ ​ — ​ ​ 1,625 ​ ​ 590,041 Total ​ $ 588,416 ​ $ 2,795,378 ​ $ 62,096 ​ $ 3,445,890 * Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities ​ The following table summarizes changes in the balance of securities whose fair value was measured using significant unobservable inputs (Level 3). ​ ​ ​ ​ ​ (in thousands) Level 3 Securities Balance as of January 1, 2024 ​ $ 62,096 Net realized and unrealized gains (losses) ​ ​ ​ Included in other comprehensive earnings (loss) ​ ​ (315) Purchases ​ ​ 12,310 Sales / Calls / Maturities ​ ​ (1,411) Balance as of June 30, 2024 ​ $ 72,680 Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - included in other comprehensive earnings (loss) ​ $ (315) ​ The amortized cost and fair value of available-for-sale fixed income securities by contractual maturity as of June 30, 2024 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2024 (in thousands) Amortized Cost Fair Value Due in one year or less ​ $ 242,522 ​ $ 239,183 Due after one year through five years ​ ​ 847,005 ​ ​ 815,300 Due after five years through 10 years ​ ​ 775,964 ​ ​ 745,887 Due after 10 years ​ ​ 548,359 ​ ​ 454,421 ABS/CMBS/MBS* ​ ​ 804,016 ​ ​ 734,736 Total available-for-sale ​ $ 3,217,866 ​ $ 2,989,527 * Asset-backed, commercial mortgage-backed and mortgage-backed securities ​ The amortized cost and fair value of available-for-sale securities at June 30, 2024 and December 31, 2023 are presented in the tables below. Amortized cost does not include the $26 million and $23 million of accrued interest receivable as of June 30, 2024 and December 31, 2023, respectively. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2024 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 442,734 ​ $ — ​ $ 258 ​ $ (8,192) ​ $ 434,800 U.S. agency ​ ​ 60,058 ​ ​ — ​ ​ 326 ​ ​ (2,075) ​ ​ 58,309 Non-U.S. government & agency ​ ​ 4,800 ​ ​ — ​ ​ — ​ ​ (972) ​ ​ 3,828 Agency MBS ​ ​ 458,944 ​ ​ — ​ ​ 915 ​ ​ (45,184) ​ ​ 414,675 ABS/CMBS/MBS* ​ ​ 345,072 ​ ​ (2) ​ ​ 1,367 ​ ​ (26,376) ​ ​ 320,061 Corporate ​ ​ 1,310,888 ​ ​ (226) ​ ​ 3,620 ​ ​ (63,502) ​ ​ 1,250,780 Municipal ​ ​ 595,370 ​ ​ — ​ ​ 1,069 ​ ​ (89,365) ​ ​ 507,074 Total Fixed Income ​ $ 3,217,866 ​ $ (228) ​ $ 7,555 ​ $ (235,666) ​ $ 2,989,527 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2023 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 312,632 ​ $ — ​ $ 1,257 ​ $ (5,858) ​ $ 308,031 U.S. agency ​ ​ 60,763 ​ ​ — ​ ​ 652 ​ ​ (1,589) ​ ​ 59,826 Non-U.S. government & agency ​ ​ 4,800 ​ ​ — ​ ​ — ​ ​ (918) ​ ​ 3,882 Agency MBS ​ ​ 460,551 ​ ​ — ​ ​ 2,636 ​ ​ (37,902) ​ ​ 425,285 ABS/CMBS/MBS* ​ ​ 308,458 ​ ​ (3) ​ ​ 611 ​ ​ (27,884) ​ ​ 281,182 Corporate ​ ​ 1,273,187 ​ ​ (303) ​ ​ 8,766 ​ ​ (56,631) ​ ​ 1,225,019 Municipal ​ ​ 634,000 ​ ​ — ​ ​ 2,238 ​ ​ (83,614) ​ ​ 552,624 Total Fixed Income ​ $ 3,054,391 ​ $ (306) ​ $ 16,160 ​ $ (214,396) ​ $ 2,855,849 * Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities ​ Allowance for Credit Losses and Unrealized Losses on Fixed Income Securities ​ A reversable allowance for credit losses is recognized on available-for-sale fixed income securities. Several criteria are reviewed to determine if securities in the fixed income portfolio should be included in the allowance for expected credit loss evaluation, including: ​ ● Changes in technology that may impair the earnings potential of the investment, ​ ● The discontinuance of a segment of business that may affect future earnings potential, ​ ● Reduction of or non-payment of interest and/or principal, ​ ● Specific concerns related to the issuer’s industry or geographic area of operation, ​ ● Significant or recurring operating losses, poor cash flows and/or deteriorating liquidity ratios and ​ ● Downgrades in credit quality by a major rating agency. ​ If changes in interest rates and credit spreads do not reasonably explain the unrealized loss for an available-for-sale security, or if any of the criteria above indicate a potential credit loss, the security is subjected to a discounted cash flow analysis. Inputs into the discounted cash flow analysis include prepayment assumptions for structured securities, default rates and recoverability rates based on credit rating. The allowance for any security is limited to the amount that the security’s fair value is below amortized cost. As of June 30, 2024, the discounted cash flow analysis resulted in an allowance for credit losses on 9 securities. The following table presents changes in the allowance for expected credit losses on available-for-sale securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, ​ Six Months Ended June 30, (in thousands) 2024 2023 2024 2023 Beginning balance ​ $ 237 ​ $ 465 ​ $ 306 ​ $ 339 Increase to allowance from securities for which credit losses were not previously recorded ​ ​ — ​ ​ 2 ​ ​ — ​ ​ 25 Reduction from securities sold during the period ​ ​ (27) ​ ​ — ​ ​ (89) ​ ​ — Net increase (decrease) from securities that had an allowance at the beginning of the period ​ ​ 18 ​ ​ (33) ​ ​ 11 ​ ​ 70 Balance as of June 30, ​ $ 228 ​ $ 434 ​ $ 228 ​ $ 434 ​ We recognized $2 million of losses on securities for which we no longer had the intent to hold until recovery during the first six months of 2023. No such losses were recognized during the first six months of 2024. ​ As of June 30, 2024, in addition to the securities included in the allowance for credit losses, the fixed income portfolio contained 1,366 securities with an unrealized loss position for which an allowance for credit losses had not been recorded. The $236 million in associated unrealized losses represents 7 percent of the fixed income portfolio’s cost basis and 6 percent of total invested assets. Isolated to these securities, unrealized losses increased slightly through the first six months of 2024, as interest rates increased during the period. Of the total 1,366 securities, 1,156 have been in an unrealized loss position for 12 consecutive months or longer. The following table illustrates the total value of fixed income securities that were in an unrealized loss position as of June 30, 2024 and December 31, 2023 after factoring in the allowance for credit losses. All fixed income securities continue to pay the expected coupon payments and we believe we will recover the amortized cost basis of available-for-sale securities that remain in an unrealized loss position. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2024 ​ December 31, 2023 (in thousands) < 12 Mos. 12 Mos. & Greater Total < 12 Mos. 12 Mos. & Greater Total U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 157,918 ​ $ 227,774 ​ $ 385,692 ​ $ 37,718 ​ $ 204,556 ​ $ 242,274 Amortized cost ​ ​ 159,088 ​ ​ 234,796 ​ ​ 393,884 ​ ​ 37,950 ​ ​ 210,182 ​ ​ 248,132 Unrealized loss ​ $ (1,170) ​ $ (7,022) ​ $ (8,192) ​ $ (232) ​ $ (5,626) ​ $ (5,858) U.S. agency ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 11,369 ​ $ 35,039 ​ $ 46,408 ​ $ 8,736 ​ $ 29,632 ​ $ 38,368 Amortized cost ​ ​ 11,507 ​ ​ 36,976 ​ ​ 48,483 ​ ​ 8,790 ​ ​ 31,167 ​ ​ 39,957 Unrealized loss ​ $ (138) ​ $ (1,937) ​ $ (2,075) ​ $ (54) ​ $ (1,535) ​ $ (1,589) Non-U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ — ​ $ 3,828 ​ $ 3,828 ​ $ — ​ $ 3,882 ​ $ 3,882 Amortized cost ​ ​ — ​ ​ 4,800 ​ ​ 4,800 ​ ​ — ​ ​ 4,800 ​ ​ 4,800 Unrealized Loss ​ $ — ​ $ (972) ​ $ (972) ​ $ — ​ $ (918) ​ $ (918) Agency MBS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 47,461 ​ $ 312,936 ​ $ 360,397 ​ $ 61,196 ​ $ 275,707 ​ $ 336,903 Amortized cost ​ ​ 47,832 ​ ​ 357,749 ​ ​ 405,581 ​ ​ 61,714 ​ ​ 313,091 ​ ​ 374,805 Unrealized loss ​ $ (371) ​ $ (44,813) ​ $ (45,184) ​ $ (518) ​ $ (37,384) ​ $ (37,902) ABS/CMBS/MBS* ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 20,533 ​ $ 178,161 ​ $ 198,694 ​ $ 12,240 ​ $ 211,436 ​ $ 223,676 Amortized cost ​ ​ 20,571 ​ ​ 204,499 ​ ​ 225,070 ​ ​ 12,367 ​ ​ 239,193 ​ ​ 251,560 Unrealized loss ​ $ (38) ​ $ (26,338) ​ $ (26,376) ​ $ (127) ​ $ (27,757) ​ $ (27,884) Corporate ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 228,328 ​ $ 801,030 ​ $ 1,029,358 ​ $ 67,402 ​ $ 822,731 ​ $ 890,133 Amortized cost ​ ​ 233,642 ​ ​ 859,218 ​ ​ 1,092,860 ​ ​ 68,345 ​ ​ 878,419 ​ ​ 946,764 Unrealized loss ​ $ (5,314) ​ $ (58,188) ​ $ (63,502) ​ $ (943) ​ $ (55,688) ​ $ (56,631) Municipal ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 54,876 ​ $ 416,438 ​ $ 471,314 ​ $ 61,218 ​ $ 391,361 ​ $ 452,579 Amortized cost ​ ​ 55,562 ​ ​ 505,117 ​ ​ 560,679 ​ ​ 61,697 ​ ​ 474,496 ​ ​ 536,193 Unrealized loss ​ $ (686) ​ $ (88,679) ​ $ (89,365) ​ $ (479) ​ $ (83,135) ​ $ (83,614) Total fixed income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 520,485 ​ $ 1,975,206 ​ $ 2,495,691 ​ $ 248,510 ​ $ 1,939,305 ​ $ 2,187,815 Amortized cost ​ ​ 528,202 ​ ​ 2,203,155 ​ ​ 2,731,357 ​ ​ 250,863 ​ ​ 2,151,348 ​ ​ 2,402,211 Unrealized loss ​ $ (7,717) ​ $ (227,949) ​ $ (235,666) ​ $ (2,353) ​ $ (212,043) ​ $ (214,396) * Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities ​ The following table shows the composition of the fixed income securities in unrealized loss positions, after factoring in the allowance for credit losses, at June 30, 2024 by the National Association of Insurance Commissioners (NAIC) rating and the generally equivalent Standard & Poor’s (S&P) and Moody’s ratings. The vast majority of the securities are rated by S&P and/or Moody’s. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equivalent ​ Equivalent ​ (dollars in thousands) ​ ​ ​ NAIC S&P Moody’s ​ Amortized ​ ​ ​ ​ Unrealized ​ Percent ​ Rating Rating Rating Cost Fair Value Loss to Total ​ 1 ​ AAA/AA/A ​ Aaa/Aa/A ​ $ 2,292,580 ​ $ 2,086,894 ​ $ (205,686) ​ 87.3 % 2 ​ BBB ​ Baa ​ ​ 388,103 ​ ​ 361,830 ​ ​ (26,273) ​ 11.1 % 3 ​ BB ​ Ba ​ ​ 30,171 ​ ​ 28,674 ​ ​ (1,497) ​ 0.6 % 4 ​ B ​ B ​ ​ 16,562 ​ ​ 15,259 ​ ​ (1,303) ​ 0.6 % 5 ​ CCC ​ Caa ​ ​ 3,121 ​ ​ 2,646 ​ ​ (475) ​ 0.2 % 6 ​ CC or lower ​ Ca or lower ​ ​ 820 ​ ​ 388 ​ ​ (432) ​ 0.2 % ​ ​ ​ ​ Total ​ $ 2,731,357 ​ $ 2,495,691 ​ $ (235,666) ​ 100.0 % ​ Other Invested Assets ​ We had $55 million of other invested assets at June 30, 2024, compared to $59 million at December 31, 2023. Other invested assets include investments in low income housing tax credit partnerships (LIHTC) and historic tax credit partnerships (HTC), membership in the Federal Home Loan Bank of Chicago (FHLBC), and investments in private funds. Our LIHTC and HTC investments are carried at amortized cost and our investment in FHLBC stock is carried at cost. Due to the nature of the LIHTC, HTC and our membership in the FHLBC, their carrying amounts approximate fair value. The private funds are carried at fair value, using each investment’s net asset value. ​ Our LIHTC interests had a balance of $9 million at June 30, 2024, compared to $10 million on December 31, 2023. Our LIHTC interests recognized amortization of $1 million as a component of income tax expense and a total tax benefit of $1 million during the second quarter of 2024 and 2023. For the six-months ended June 30, 2024, our LIHTC interests recognized amortization of $1 million and a total tax benefit of $1 million, compared to $2 million of amortization and $2 million of tax benefit for the same period in 2023. Our unfunded commitment for our LIHTC investments was less than $1 million at June 30, 2024 and will be paid out in installments through 2035. ​ Our HTC investment had a balance of $11 million at June 30, 2024, compared to $13 million at December 31, 2023. Our HTC investment recognized $1 million of amortization as a component of income tax expense and a total tax benefit of $1 million during the second quarter of 2024 and 2023. For the six-months ended June 30, 2024 and 2023, our HTC investment recognized amortization of $2 million and a total tax benefit of $3 million. ​ As of June 30, 2024, $57 million of investments ​ Our investments in private funds totaled $25 million as of June 30, 2024, down from $28 million as of December 31, 2023, and had $4 million of associated unfunded commitments at June 30, 2024. Our interest in private funds is generally restricted from being transferred or otherwise redeemed without prior consent by the respective entities, and the timed dissolution of the partnerships would trigger redemption. ​ Investments in Unconsolidated Investees ​ We had $67 million of investments in unconsolidated investees at June 30, 2024, compared to $57 million at December 31, 2023. At June 30, 2024, our investment in Prime Holdings Insurance Services, Inc. (Prime) was $67 million and other investments in unconsolidated investees totaled less than $1 million. ​ Cash and Short-Term Investments ​ Cash consists of uninvested balances in bank accounts. Short-term investments consist of investments with original maturities of 90 days or less, primarily AAA-rated government money market funds. Short-term investments are carried at cost. We had a cash and short-term investment balance of $50 million and $126 million, respectively, at June 30, 2024, compared to $36 million and $135 million, respectively, at December 31, 2023.

Historical Loss And LAE Develop

Historical Loss And LAE Development	6 Months Ended
	Jun. 30, 2024
Historical Loss And L A E Development Disclosure [Abstract]
Historical Loss And LAE Development	3. HISTORICAL LOSS AND LAE DEVELOPMENT ​ The following table is a reconciliation of our unpaid losses and settlement expenses (LAE) for the first six months of 2024 and 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ ​ Ended June 30, (in thousands) 2024 2023 Unpaid losses and LAE at beginning of year ​ ​ ​ ​ ​ ​ Gross ​ $ 2,446,025 ​ $ 2,315,637 Ceded ​ ​ (757,349) ​ ​ (740,089) Net ​ $ 1,688,676 ​ $ 1,575,548 ​ ​ ​ ​ ​ ​ ​ Increase (decrease) in incurred losses and LAE ​ ​ ​ ​ ​ ​ Current accident year ​ $ 376,546 ​ $ 339,951 Prior accident years ​ ​ (64,923) ​ ​ (71,520) Total incurred ​ $ 311,623 ​ $ 268,431 ​ ​ ​ ​ ​ ​ ​ Loss and LAE payments for claims incurred ​ ​ ​ ​ ​ ​ Current accident year ​ $ (40,078) ​ $ (30,978) Prior accident years ​ ​ (197,887) ​ ​ (172,282) Total paid ​ $ (237,965) ​ $ (203,260) ​ ​ ​ ​ ​ ​ ​ Net unpaid losses and LAE at June 30, ​ $ 1,762,334 ​ $ 1,640,719 ​ ​ ​ ​ ​ ​ ​ Unpaid losses and LAE at June 30, ​ ​ ​ ​ ​ ​ Gross ​ $ 2,544,622 ​ $ 2,361,577 Ceded ​ ​ (782,288) ​ ​ (720,858) Net ​ $ 1,762,334 ​ $ 1,640,719 ​ For the first six months of 2024, incurred losses and LAE included $65 million of favorable development on prior years’ loss reserves, largely from accident years 2016, 2017, 2019, 2020, 2022 and 2023. Marine, surety, general liability, commercial property, executive products, personal umbrella, professional services and commercial excess were drivers of the favorable development. No products experienced significant adverse development. ​ For the first six months of 2023, incurred losses and LAE included $72 million of favorable development on prior years’ loss reserves, largely from accident years 2018 through 2022. Commercial excess, professional services, surety, general liability, personal umbrella, marine and commercial property were drivers of the favorable development. No products experienced significant adverse development.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2024
Income Tax Disclosure
Income Taxes	4. INCOME TAXES ​ Our effective tax rate for the three and six months ended June 30, 2024 was 20.6 percent and 20.3 percent, respectively, compared to 19.1 percent and 19.4 percent, respectively, for the same periods in 2023. Effective rates are dependent upon components of pretax earnings and the related tax effects. The effective tax rate was higher for the three and six-month periods in 2024 due to lower levels of tax-favored adjustments and higher levels of pretax income, which decreased the percentage impact of tax-favored adjustments. ​ Income tax expense attributable to income from operations for the three and six-month periods ended June 30, 2024 and 2023 differed from the amounts computed by applying the U.S. federal tax rate of 21 percent to pretax income by the items detailed in the table below. In interim periods, income taxes are adjusted to reflect the effective tax rate we anticipate for the year, with adjustments flowing through the other items, net line. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months Ended June 30, ​ For the Six Months Ended June 30, 2024 ​ ​ ​ 2024 ​ 2023 ​ 2024 ​ 2023 ​ (in thousands) Amount % Amount % Amount % Amount % ​ Provision for income taxes at the statutory rate of 21% ​ $ 21,694 ​ 21.0 % $ 20,167 ​ 21.0 % $ 55,292 ​ 21.0 % $ 45,953 ​ 21.0 % Increase (reduction) in taxes resulting from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Excess tax benefit on share-based compensation ​ ​ (422) ​ (0.4) % ​ (878) ​ (0.9) % ​ (2,297) ​ (0.8) % ​ (2,868) ​ (1.3) % Tax exempt interest income ​ ​ (249) ​ (0.2) % ​ (274) ​ (0.3) % ​ (509) ​ (0.2) % ​ (557) ​ (0.3) % Dividends received deduction ​ ​ (234) ​ (0.2) % ​ (209) ​ (0.2) % ​ (468) ​ (0.2) % ​ (433) ​ (0.2) % Tax credit ​ ​ (768) ​ (0.8) % ​ (780) ​ (0.8) % ​ (1,536) ​ (0.6) % ​ (1,559) ​ (0.7) % ESOP dividends paid deduction ​ ​ (151) ​ (0.2) % ​ (144) ​ (0.2) % ​ (290) ​ (0.1) % ​ (281) ​ (0.1) % Nondeductible expenses ​ ​ 946 ​ 0.9 % ​ 745 ​ 0.8 % ​ 1,659 ​ 0.6 % ​ 1,346 ​ 0.6 % Other items, net ​ ​ 495 ​ 0.5 % ​ (248) ​ (0.3) % ​ 1,551 ​ 0.6 % ​ 758 ​ 0.4 % Total tax expense ​ $ 21,311 ​ 20.6 % $ 18,379 ​ 19.1 % $ 53,402 ​ 20.3 % $ 42,359 ​ 19.4 % ​ We have recorded our deferred tax assets and liabilities using the statutory federal tax rate of 21 percent. We believe it is more likely than not that all deferred tax assets will be recovered, given the carry back availability as well as the result of future operations, which we believe will generate sufficient taxable income to realize the deferred tax asset.

Stock Based Compensation

Stock Based Compensation	6 Months Ended
	Jun. 30, 2024
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Based Compensation	5. STOCK BASED COMPENSATION ​ Our RLI Corp. Long-Term Incentive Plan (2015 LTIP) was in place from 2015 to 2023. The 2015 LTIP provided for equity-based compensation, including stock options and restricted stock units, up to a maximum of 4,000,000 shares of common stock (subject to adjustment for changes in our capitalization and other events). Between 2015 and 2023, we granted 3,291,388 awards under the 2015 LTIP. The 2015 LTIP was replaced in 2023. ​ In 2023, our shareholders approved the 2023 RLI Corp. Long-Term Incentive Plan (2023, LTIP), which provides for equity-based compensation. In conjunction with the adoption of the 2023 LTIP, effective May 4, 2023, awards are no longer granted under the 2015 LTIP. Awards under the 2023 LTIP may be in the form of restricted stock, restricted stock units, stock options (incentive or non-qualified), stock appreciation rights, performance units as well as other stock-based awards. Eligibility under the 2023 LTIP is limited to employees, directors, consultants and independent contractors of the Company or any affiliate. The granting of awards under the 2023 LTIP is solely at the discretion of the Human Capital and Compensation Committee of the board of directors or its delegate. The maximum number of shares of common stock available for distribution under the 2023 LTIP is 4,004,891 shares (subject to adjustment for changes in our capitalization and other events). Since the plan’s approval in 2023, we have granted 357,001 awards under the 2023 LTIP, including 161,463 thus far in 2024. ​ Compensation expense is based on the probable number of awards expected to vest. The total compensation expense related to equity awards was $2.2 million and $4.0 million in the three and six-month periods ended June 30, 2024, respectively, compared to $2.2 million and $4.7 million, respectively, for the same periods in 2023. The total income tax benefit was $0.3 million and $0.6 million for the three and six-month periods ended June 30, 2024, compared to $0.3 million and $0.8 million, respectively, for the same periods in 2023. Total unrecognized compensation expense relating to outstanding and unvested awards was $9 million, which will be recognized over the weighted average vesting period of 2.74 years. ​ Stock Options ​ Under the 2023 LTIP, as under the 2015 LTIP, we grant stock options for shares with an exercise price equal to the fair market value of the shares at the date of grant (subject to adjustments for changes in our capitalization, special dividends and other events as set forth in such plans). Options generally vest and become exercisable over a five-year period and expire eight years after grant. ​ For most participants, the requisite service period and vesting period will be the same. For participants who are retirement eligible, defined by the plan as those individuals whose age and years of service equals 75 or greater, the requisite service period is deemed to be met and options are immediately expensed on the date of grant. For participants who will become retirement eligible during the vesting period, the requisite service period over which expense is recognized is the period between the grant date and the attainment of retirement eligibility. Shares issued upon option exercise are newly issued shares. ​ The following tables summarize option activity for the six-month period ended June 30, 2024: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ Aggregate ​ ​ ​ ​ Weighted ​ Average ​ Intrinsic ​ ​ ​ ​ Average ​ Remaining ​ Value ​ Options Exercise Price Contractual Life (in 000’s) Outstanding options at January 1, 2024 ​ 1,641,710 ​ $ 92.62 ​ ​ ​ ​ ​ Options granted ​ 141,932 ​ ​ 141.73 ​ ​ ​ ​ ​ Options exercised ​ (120,940) ​ ​ 67.25 ​ ​ ​ ​ ​ Options canceled/forfeited ​ (6,900) ​ ​ 105.93 ​ ​ ​ ​ ​ Outstanding options at June 30, 2024 ​ 1,655,802 ​ $ 98.62 ​ 4.51 ​ $ 69,933 Exercisable options at June 30, 2024 ​ 983,166 ​ $ 85.13 ​ 3.39 ​ $ 54,623 ​ The intrinsic value of options exercised, which is the difference between the fair value and the exercise price, was $9 million and $16 million during the first six months of 2024 and 2023, respectively. ​ The fair value of options was estimated using a Black-Scholes based option pricing model with the following weighted average grant-date assumptions and weighted average fair values as of June 30: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2024 2023 ​ Weighted-average fair value of grants ​ $ 31.09 ​ $ 26.79 ​ Risk-free interest rates ​ ​ 4.91 % ​ 3.44 % Dividend yield ​ ​ 2.30 % ​ 2.29 % Expected volatility ​ ​ 23.08 % ​ 22.95 % Expected option life ​ ​ 5.00 years ​ 4.94 years ​ The risk-free rate was determined based on U.S. treasury yields that most closely approximated the options’ expected life. The dividend yield was determined based on the average annualized quarterly dividends paid during the most recent five-year period and incorporated a consideration for special dividends paid in recent history. The expected volatility was calculated based on the median of the rolling volatilities for the expected life of the options. The expected option life was determined based on historical exercise behavior and the assumption that all outstanding options will be exercised at the midpoint of the current date and remaining contractual term, adjusted for the demographics of the current year’s grant. ​ Restricted Stock Units ​ In addition to stock options, restricted stock units (RSUs) are granted with a value equal to the closing stock price of the Company’s stock on the dates the units are granted. For employees, these units generally have a three-year cliff vesting, but have an accelerated vesting feature for participants who are retirement eligible, defined by the plan as those individuals whose age and years of service equals 75 or greater. For directors, these units vest on the earlier of one year from the date of grant or the next annual shareholders meeting. In addition, the RSUs have dividend participation, which accrue as additional units and are settled with granted stock units at the end of the vesting period. The total fair value of restricted stock units that vested was $2 million and $1 million during the first six months of 2024 and 2023, respectively. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ RSUs Fair Value Nonvested at January 1, 2024 ​ 45,093 ​ $ 125.16 Granted ​ 19,531 ​ ​ 142.83 Reinvested ​ 179 ​ ​ 143.82 Vested ​ (17,198) ​ ​ 122.96 Forfeited ​ (606) ​ ​ 132.42 Nonvested at June 30, 2024 ​ 46,999 ​ $ 133.29 ​

Operating Segment Information

Operating Segment Information	6 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Operating Segment Information	6. OPERATING SEGMENT INFORMATION Selected information by operating segment is presented in the table below. Additionally, the table reconciles segment totals to total earnings and total revenues. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months Revenues ​ Ended June 30, ​ Ended June 30, (in thousands) 2024 2023 2024 2023 Casualty ​ $ 209,100 ​ $ 187,048 ​ $ 407,376 ​ $ 373,079 Property ​ ​ 134,097 ​ ​ 101,841 ​ ​ 263,508 ​ ​ 190,608 Surety ​ ​ 35,868 ​ ​ 33,391 ​ ​ 68,857 ​ ​ 66,316 Net premiums earned ​ $ 379,065 ​ $ 322,280 ​ $ 739,741 ​ $ 630,003 Net investment income ​ ​ 33,961 ​ ​ 28,788 ​ ​ 66,808 ​ ​ 55,872 Net realized gains (losses) ​ ​ (192) ​ ​ 5,580 ​ ​ 5,802 ​ ​ 20,200 Net unrealized gains on equity securities ​ ​ 3,608 ​ ​ 25,214 ​ ​ 48,922 ​ ​ 40,710 Total consolidated revenue ​ $ 416,442 ​ $ 381,862 ​ $ 861,273 ​ $ 746,785 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Earnings ​ ​ ​ ​ ​ ​ (in thousands) 2024 2023 2024 2023 Casualty ​ $ 10,315 ​ $ 6,977 ​ $ 23,989 ​ $ 38,808 Property ​ ​ 53,180 ​ ​ 25,877 ​ ​ 110,896 ​ ​ 54,260 Surety ​ ​ 6,529 ​ ​ 8,347 ​ ​ 12,834 ​ ​ 16,023 Net underwriting income ​ $ 70,024 ​ $ 41,201 ​ $ 147,719 ​ $ 109,091 Net investment income ​ ​ 33,961 ​ ​ 28,788 ​ ​ 66,808 ​ ​ 55,872 Net realized gains (losses) ​ ​ (192) ​ ​ 5,580 ​ ​ 5,802 ​ ​ 20,200 Net unrealized gains on equity securities ​ ​ 3,608 ​ ​ 25,214 ​ ​ 48,922 ​ ​ 40,710 General corporate expense and interest on debt ​ ​ (5,744) ​ ​ (6,266) ​ ​ (12,372) ​ ​ (12,488) Equity in earnings of unconsolidated investees ​ ​ 1,646 ​ ​ 1,514 ​ ​ 6,415 ​ ​ 5,437 Earnings before income taxes ​ $ 103,303 ​ $ 96,031 ​ $ 263,294 ​ $ 218,822 Income tax expense ​ ​ 21,311 ​ ​ 18,379 ​ ​ 53,402 ​ ​ 42,359 Net earnings ​ $ 81,992 ​ $ 77,652 ​ $ 209,892 ​ $ 176,463 ​ The following table further summarizes revenues by major product type within each operating segment: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months Net Premiums Earned ​ Ended June 30, ​ Ended June 30, (in thousands) 2024 2023 2024 2023 Casualty ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial excess and personal umbrella ​ $ 85,986 ​ $ 69,261 ​ $ 166,021 ​ $ 136,843 Commercial transportation ​ ​ 29,323 ​ ​ 25,398 ​ ​ 56,624 ​ ​ 50,630 General liability ​ ​ 26,104 ​ ​ 26,016 ​ ​ 51,516 ​ ​ 51,916 Professional services ​ ​ 26,000 ​ ​ 24,602 ​ ​ 51,085 ​ ​ 48,959 Small commercial ​ ​ 19,459 ​ ​ 18,455 ​ ​ 37,796 ​ ​ 36,396 Executive products ​ ​ 5,448 ​ ​ 6,153 ​ ​ 11,363 ​ ​ 12,506 Other casualty ​ ​ 16,780 ​ ​ 17,163 ​ ​ 32,971 ​ ​ 35,829 Total ​ $ 209,100 ​ $ 187,048 ​ $ 407,376 ​ $ 373,079 Property ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial property ​ $ 87,400 ​ $ 60,219 ​ $ 175,005 ​ $ 109,481 Marine ​ ​ 37,069 ​ ​ 32,412 ​ ​ 69,637 ​ ​ 63,048 Other property ​ ​ 9,628 ​ ​ 9,210 ​ ​ 18,866 ​ ​ 18,079 Total ​ $ 134,097 ​ $ 101,841 ​ $ 263,508 ​ $ 190,608 Surety ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Transactional ​ $ 12,308 ​ $ 11,887 ​ $ 24,416 ​ $ 23,934 Commercial ​ ​ 12,700 ​ ​ 12,505 ​ ​ 23,325 ​ ​ 24,923 Contract ​ ​ 10,860 ​ ​ 8,999 ​ ​ 21,116 ​ ​ 17,459 Total ​ $ 35,868 ​ $ 33,391 ​ $ 68,857 ​ $ 66,316 Grand Total ​ $ 379,065 ​ $ 322,280 ​ $ 739,741 ​ $ 630,003 ​

Leases

Leases	6 Months Ended
	Jun. 30, 2024
Leases [Abstract]
Leases	7. LEASES ​ Right-of-use (ROU) assets are included in the other assets line item and lease liabilities are included in the other liabilities line item of the consolidated balance sheet. We determine if a contract contains a lease at inception and recognize operating lease ROU assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the commencement date in determining the present value of future payments. Lease agreements may include options to extend or terminate. The options are exercised at our discretion and are included in operating lease liabilities if it is reasonably certain the option will be exercised. Lease agreements have lease and non-lease components, which are accounted for as a single lease component. Operating lease costs for future minimum lease payments are recognized on a straight-line basis over the lease terms. Variable lease costs are expensed in the period in which the obligations are incurred. Sublease income is recognized on a straight-line basis over the sublease term. ​ The Company’s operating lease obligations are for branch office facilities. The components of lease expense and other lease information as of and during the three and six-month periods ended June 30, 2024 and 2023 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months ​ ​ Ended June 30, ​ Ended June 30, (in thousands) 2024 2023 2024 2023 Operating lease cost ​ $ 1,153 ​ $ 1,239 ​ $ 2,334 ​ $ 2,508 Variable lease cost ​ ​ 260 ​ ​ 444 ​ ​ 508 ​ ​ 882 Sublease income ​ ​ (42) ​ ​ (139) ​ ​ (85) ​ ​ (277) Total lease cost ​ $ 1,371 ​ $ 1,544 ​ $ 2,757 ​ $ 3,113 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash paid for amounts included in measurement of lease liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating cash outflows from operating leases ​ $ 1,105 ​ $ 1,357 ​ $ 2,168 ​ $ 2,755 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ 333 ​ $ 943 ​ $ 3,789 ​ $ 984 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reduction to ROU assets resulting from reduction to lease liabilities ​ $ — ​ $ — ​ $ — ​ $ 200 ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) June 30, 2024 December 31, 2023 ​ Operating lease ROU assets ​ $ 15,417 ​ $ 13,666 ​ Operating lease liabilities ​ $ 16,783 ​ $ 14,880 ​ Weighted-average remaining lease term - operating leases ​ ​ 6.14 years ​ 6.08 years Weighted-average discount rate - operating leases ​ ​ 3.56 % ​ 3.21 % ​ Future minimum lease payments under non-cancellable leases as of June 30, 2024 were as follows: ​ ​ ​ ​ ​ (in thousands) June 30, 2024 2024 ​ $ 1,994 2025 ​ ​ 4,197 2026 ​ ​ 3,473 2027 ​ ​ 2,107 2028 ​ ​ 1,537 2029 ​ ​ 1,443 Thereafter ​ ​ 4,489 Total future minimum lease payments ​ $ 19,240 Less imputed interest ​ ​ (2,457) Total operating lease liability ​ $ 16,783 ​

Acquisitions and Dispositions

Acquisitions and Dispositions	6 Months Ended
	Jun. 30, 2024
Business Combination and Asset Acquisition [Abstract]
Acquisitions and Dispositions	8. ACQUISITONS AND DISPOSTIONS ​ On September 30, 2022, RLI Corp. completed the sale of its equity method investment in Maui Jim, Inc. to Kering Eyewear. During the first quarter of 2023, the payout of the working capital escrow resulted in the recognition of a $14 million gain that was recorded in the net realized gain line item of the statement of earnings.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ 81,992	$ 127,900	$ 77,652	$ 98,811	$ 209,892	$ 176,463

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 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

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation	A. BASIS OF PRESENTATION ​ The unaudited interim condensed consolidated financial statements of RLI Corp. (the Company) and subsidiaries have been prepared in accordance with generally accepted accounting principles in the United States of America (GAAP). These condensed consolidated financial statements do not include all the disclosures required by GAAP for annual financial statements and should be read in conjunction with our 2023 Annual Report on Form 10-K. In the opinion of the Company’s management, the condensed consolidated financial statements reflect all adjustments, of a normal and recurring nature, that are necessary for fair financial statement presentation. The results of operations for any interim period are not necessarily indicative of the operating results for a full year. ​ The preparation of the unaudited condensed consolidated financial statements requires management to make estimates and assumptions relating to the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of revenue and expenses during the period. These estimates are inherently subject to change and actual results could differ significantly from these estimates.
Adopted Accounting Standards	B. ADOPTED ACCOUNTING STANDARDS ​ No new accounting standards applicable in 2024 materially impact our financial statements.
Prospective Accounting Standards	​ C. PROSPECTIVE ACCOUNTING STANDARDS ​ 2023-07—Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures ​ The guidance in ASU 2023-07 was designed to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. This ASU is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Although the Company continues to evaluate the impact of adopting this new accounting standard, the amendments are disclosure-related and should not have a material impact on our financial statements. ​ 2023-09—Income Taxes (Topic 740): Improvements to Income Tax Disclosures ​ The guidance in ASU 2023-09 was designed to increase transparency about income tax information through improvements to the rate reconciliation and disclosure of income taxes paid. This ASU is effective for fiscal years beginning after December 15, 2024. Although the Company continues to evaluate the impact of adopting this new accounting standard, the amendments are disclosure-related and should not have a material impact on our financial statements.
Reinsurance	​ D. REINSURANCE ​ Ceded unearned premiums and reinsurance balances recoverable on unpaid losses and settlement expenses are reported separately as an asset, rather than being netted with the related liability, since reinsurance does not relieve the Company of our liability to policyholders. Such balances are subject to the credit risk associated with the individual reinsurer. We continually monitor the financial condition of our reinsurers and actively follow up on any past due or disputed amounts. As part of our monitoring efforts, we review reinsurers’ annual financial statements and Securities and Exchange Commission filings for those that are publicly traded. We also review insurance industry developments that may impact the financial condition of our reinsurers. We analyze the credit risk associated with our reinsurance balances recoverable by monitoring the AM Best and Standard & Poor’s (S&P) ratings of our reinsurers. We subject our reinsurance balances recoverable to detailed recoverability tests, including a segment-based analysis using the average default rating percentage by S&P rating, which assists the Company in assessing the sufficiency of its allowance. Additionally, we perform an in-depth reinsurer financial condition analysis prior to the renewal of our reinsurance placements. ​ Our policy is to charge to earnings, in the form of an allowance, an estimate of unrecoverable amounts from reinsurers. This allowance is reviewed on an ongoing basis to ensure that the amount makes a reasonable provision for reinsurance balances that we may be unable to recover. Once regulatory action (such as receivership, finding of insolvency, order of conservation or order of liquidation) is taken against a reinsurer, the paid and unpaid recoverable balances for the reinsurer are specifically identified and written off through the use of our allowance for estimated unrecoverable amounts from reinsurers. When we write-off such a balance, it is done in full. We then re-evaluate the overall allowance and determine whether the balance is sufficient and, if needed, an additional allowance is recognized. ​ The allowances for uncollectible amounts on paid and unpaid reinsurance balances recoverable were $16 million and $11 million, respectively, at June 30, 2024 and December 31, 2023. Changes in the allowances were due to changes in the amount of reinsurance balances outstanding, the composition of reinsurers from whom the balances were recoverable and their associated S&P default ratings. No write-offs were applied to the allowances in the first six months of 2024 and less than $1 million was recovered. ​
Intangible Assets	E. INTANGIBLE ASSETS ​ The composition of goodwill and intangible assets at June 30, 2024 and December 31, 2023 is detailed in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (in thousands) 2024 2023 Goodwill ​ ​ ​ ​ ​ ​ Surety ​ $ 40,816 ​ $ 40,816 Casualty ​ ​ 5,246 ​ ​ 5,246 Total goodwill ​ $ 46,062 ​ $ 46,062 Indefinite-lived intangibles ​ ​ 7,500 ​ ​ 7,500 Total goodwill and intangibles ​ $ 53,562 ​ $ 53,562 ​ Annual impairment assessments were performed on our goodwill and state insurance license indefinite-lived intangible assets during the second quarter of 2024. Based upon these reviews, none of the assets were impaired. In addition, there were no triggering events as of June 30, 2024 that would suggest an updated impairment test would be needed for our goodwill and intangible assets.
Earnings Per Share	F. EARNINGS PER SHARE ​ Basic earnings per share (EPS) is computed by dividing income available to common shareholders by the weighted-average number of common shares outstanding for the period. Diluted EPS reflects the dilution that could occur if securities or other contracts to issue common stock or common stock equivalents were exercised or converted into common stock. When inclusion of these items increases the earnings per share or reduces the loss per share, the effect on earnings is anti-dilutive. Under these circumstances, the diluted net earnings or net loss per share is computed excluding these items. The following represents a reconciliation of the numerator and denominator of the basic and diluted EPS computations contained in the unaudited condensed consolidated financial statements: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Three Months ​ ​ Ended June 30, 2024 ​ Ended June 30, 2023 ​ ​ Income ​ Shares ​ Per Share ​ Income ​ Shares ​ Per Share (in thousands, except per share data) (Numerator) (Denominator) Amount (Numerator) (Denominator) Amount Basic EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 81,992 ​ 45,737 ​ $ 1.79 ​ $ 77,652 ​ 45,591 ​ $ 1.70 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 442 ​ ​ ​ ​ ​ — ​ 453 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 81,992 ​ 46,179 ​ $ 1.78 ​ $ 77,652 ​ 46,044 ​ $ 1.69 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ For the Six Months ​ ​ Ended June 30, 2024 ​ Ended June 30, 2023 ​ ​ Income ​ Shares ​ Per Share ​ Income ​ Shares ​ Per Share (in thousands, except per share data) (Numerator) (Denominator) Amount (Numerator) (Denominator) Amount Basic EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 209,892 ​ 45,709 ​ $ 4.59 ​ $ 176,463 ​ 45,560 ​ $ 3.87 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 460 ​ ​ ​ ​ ​ — ​ 485 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 209,892 ​ 46,169 ​ $ 4.55 ​ $ 176,463 ​ 46,045 ​ $ 3.83 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 114 ​ ​ ​ ​ ​ ​ ​ ​ 118 ​ ​ ​ ​
Comprehensive Earnings	G. COMPREHENSIVE EARNINGS ​ Our comprehensive earnings include net earnings plus after-tax unrealized gains and losses on our available-for-sale fixed income portfolio. In reporting the components of comprehensive earnings, we used the federal statutory tax rate of 21 percent. Other comprehensive earnings (loss), as shown in the consolidated statements of earnings and comprehensive earnings, is net of tax benefit of $2 million for the second quarter of 2024, compared to $5 million of tax benefit for the same period in 2023. For the six-month period ended June 30, 2024, other comprehensive earnings (loss) is net of tax benefit of $5 million, compared to $5 million of tax expense for the same period in 2023. ​ Unrealized losses, net of tax, recognized in other comprehensive earnings (loss) were $21 million for the first six months of 2024, compared to $18 million of unrealized gains, net of tax, during the same period last year. The unrealized losses in 2024 were attributable to an increase in interest rates, which decreased the fair value of securities held in the fixed income portfolio. During 2023, modestly tighter credit spreads on relatively steady interest rates increased the fair value of securities held in the fixed income portfolio. ​ The following table illustrates the changes in the balance of each component of accumulated other comprehensive earnings (loss) for each period presented in the unaudited condensed consolidated financial statements: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ For the Three Months ​ For the Six Months ​ ​ Ended June 30, ​ Ended June 30, Unrealized Gains/Losses on Available-for-Sale Securities 2024 2023 2024 2023 Beginning balance ​ $ (178,974) ​ $ (191,369) ​ $ (166,303) ​ $ (229,076) Other comprehensive earnings (loss) before reclassifications ​ ​ (8,571) ​ ​ (20,347) ​ ​ (21,846) ​ ​ 15,908 Amounts reclassified from accumulated other comprehensive earnings ​ ​ 728 ​ ​ 626 ​ ​ 1,332 ​ ​ 2,078 Net current-period other comprehensive earnings (loss) ​ $ (7,843) ​ $ (19,721) ​ $ (20,514) ​ $ 17,986 Ending balance ​ $ (186,817) ​ $ (211,090) ​ $ (186,817) ​ $ (211,090) Balance of securities for which an allowance for credit losses has been recognized in net earnings ​ ​ ​ ​ ​ ​ ​ $ 1,463 ​ $ 1,053 ​ Credit losses on or the sale of an available-for-sale security results in amounts being reclassified from accumulated other comprehensive earnings (loss) to current period net earnings. The effects of reclassifications out of accumulated other comprehensive earnings (loss) by the respective line items of net earnings are presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amount Reclassified from Accumulated Other ​ ​ ​ (in thousands) ​ Comprehensive Earnings (Loss) ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months ​ ​ ​ Component of Accumulated ​ Ended June 30, ​ Ended June 30, ​ ​ Affected line item in the Other Comprehensive Earnings (Loss) 2024 2023 2024 2023 Statement of Earnings Unrealized gains and losses on available-for-sale securities ​ $ (931) ​ $ (824) ​ $ (1,765) ​ $ (2,536) ​ ​ Net realized gains (losses) ​ ​ ​ 9 ​ ​ 31 ​ ​ 79 ​ ​ (95) ​ ​ Credit gains (losses) presented within net realized gains ​ ​ $ (922) ​ $ (793) ​ $ (1,686) ​ $ (2,631) ​ ​ Earnings (loss) before income taxes ​ ​ ​ 194 ​ ​ 167 ​ ​ 354 ​ ​ 553 ​ ​ Income tax (expense) benefit ​ ​ $ (728) ​ $ (626) ​ $ (1,332) ​ $ (2,078) ​ ​ Net earnings (loss) ​
Fair Value Measurements	H. FAIR VALUE MEASUREMENTS ​ Fair value is defined as the price in the principal market that would be received for an asset to facilitate an orderly transaction between market participants on the measurement date. We determined the fair value of certain financial instruments based on their underlying characteristics and relevant transactions in the marketplace. We maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. ​ The following are the levels of the fair value hierarchy and a brief description of the type of valuation inputs that are used to establish each level. Financial assets are classified based upon the lowest level of significant input that is used to determine fair value. ​ Level 1 ​ Level 2 ​ Level 3 ​ As a part of management’s process to determine fair value, we utilize widely recognized, third-party pricing sources to determine our fair values. We have obtained an understanding of the third-party pricing sources’ valuation methodologies and inputs. The following is a description of the valuation techniques used for financial assets that are measured at fair value, including the general classification of such assets pursuant to the fair value hierarchy. ​ Corporate, Agencies, Government and Municipal Bonds: ​ Mortgage-backed Securities (MBS)/Commercial Mortgage-backed Securities (CMBS) and Asset-backed Securities (ABS): ​ Regulation D Private Placement Securities: observable and unobservable inputs. Observable inputs include public corporate spread matrices classified by sector, rating and average life, as well as investment and non-investment grade matrices created from fixed income indices. Unobservable inputs include a liquidity spread premium calculated based on public corporate spread and private corporate spread matrices. The quantitative detail of the liquidity spread premium is neither provided nor reasonably available to the Company. An increase to the credit spread assumptions would result in a lower fair value. ​ For all of our fixed income securities classified as Level 2, we periodically conduct a review to assess the reasonableness of the fair values provided by our pricing services. Our review consists of a two-pronged approach. First, we compare prices provided by our pricing services to those provided by an additional source. In some cases, we obtain prices from securities brokers and compare them to the prices provided by our pricing services. If discrepancies are found in our comparisons, we compare our prices to actual reported trade data for like securities. No changes to the fair values supplied by our pricing services have occurred as a result of our reviews. Based on these assessments, we have determined that the fair values of our Level 2 fixed income securities provided by our pricing services are reasonable. ​ Equity Securities: ​ Due to the relatively short-term nature of cash, short-term investments, accounts receivable and accounts payable, their carrying amounts are reasonable estimates of fair value. Our investments in private funds, classified as other invested assets, are measured using the investments’ net asset value per share and are not categorized within the fair value hierarchy.

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Schedule of Goodwill and Intangible Assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (in thousands) 2024 2023 Goodwill ​ ​ ​ ​ ​ ​ Surety ​ $ 40,816 ​ $ 40,816 Casualty ​ ​ 5,246 ​ ​ 5,246 Total goodwill ​ $ 46,062 ​ $ 46,062 Indefinite-lived intangibles ​ ​ 7,500 ​ ​ 7,500 Total goodwill and intangibles ​ $ 53,562 ​ $ 53,562
Schedule of Reconciliation of Numerator and Denominator of the Basic and Diluted Earnings Per Share Computations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Three Months ​ ​ Ended June 30, 2024 ​ Ended June 30, 2023 ​ ​ Income ​ Shares ​ Per Share ​ Income ​ Shares ​ Per Share (in thousands, except per share data) (Numerator) (Denominator) Amount (Numerator) (Denominator) Amount Basic EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 81,992 ​ 45,737 ​ $ 1.79 ​ $ 77,652 ​ 45,591 ​ $ 1.70 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 442 ​ ​ ​ ​ ​ — ​ 453 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 81,992 ​ 46,179 ​ $ 1.78 ​ $ 77,652 ​ 46,044 ​ $ 1.69 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ For the Six Months ​ ​ Ended June 30, 2024 ​ Ended June 30, 2023 ​ ​ Income ​ Shares ​ Per Share ​ Income ​ Shares ​ Per Share (in thousands, except per share data) (Numerator) (Denominator) Amount (Numerator) (Denominator) Amount Basic EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 209,892 ​ 45,709 ​ $ 4.59 ​ $ 176,463 ​ 45,560 ​ $ 3.87 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 460 ​ ​ ​ ​ ​ — ​ 485 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 209,892 ​ 46,169 ​ $ 4.55 ​ $ 176,463 ​ 46,045 ​ $ 3.83 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 114 ​ ​ ​ ​ ​ ​ ​ ​ 118 ​ ​ ​ ​
Schedule of Changes in the Balance of Each Component of Accumulated Other Comprehensive Earnings (Loss)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ For the Three Months ​ For the Six Months ​ ​ Ended June 30, ​ Ended June 30, Unrealized Gains/Losses on Available-for-Sale Securities 2024 2023 2024 2023 Beginning balance ​ $ (178,974) ​ $ (191,369) ​ $ (166,303) ​ $ (229,076) Other comprehensive earnings (loss) before reclassifications ​ ​ (8,571) ​ ​ (20,347) ​ ​ (21,846) ​ ​ 15,908 Amounts reclassified from accumulated other comprehensive earnings ​ ​ 728 ​ ​ 626 ​ ​ 1,332 ​ ​ 2,078 Net current-period other comprehensive earnings (loss) ​ $ (7,843) ​ $ (19,721) ​ $ (20,514) ​ $ 17,986 Ending balance ​ $ (186,817) ​ $ (211,090) ​ $ (186,817) ​ $ (211,090) Balance of securities for which an allowance for credit losses has been recognized in net earnings ​ ​ ​ ​ ​ ​ ​ $ 1,463 ​ $ 1,053
Schedule of Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Loss)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amount Reclassified from Accumulated Other ​ ​ ​ (in thousands) ​ Comprehensive Earnings (Loss) ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months ​ ​ ​ Component of Accumulated ​ Ended June 30, ​ Ended June 30, ​ ​ Affected line item in the Other Comprehensive Earnings (Loss) 2024 2023 2024 2023 Statement of Earnings Unrealized gains and losses on available-for-sale securities ​ $ (931) ​ $ (824) ​ $ (1,765) ​ $ (2,536) ​ ​ Net realized gains (losses) ​ ​ ​ 9 ​ ​ 31 ​ ​ 79 ​ ​ (95) ​ ​ Credit gains (losses) presented within net realized gains ​ ​ $ (922) ​ $ (793) ​ $ (1,686) ​ $ (2,631) ​ ​ Earnings (loss) before income taxes ​ ​ ​ 194 ​ ​ 167 ​ ​ 354 ​ ​ 553 ​ ​ Income tax (expense) benefit ​ ​ $ (728) ​ $ (626) ​ $ (1,332) ​ $ (2,078) ​ ​ Net earnings (loss)

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2024
Investments Debt And Equity Securities [Abstract]
Schedule of Disposition of Fixed Income and Equity Securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Sales ​ Proceeds ​ Gross Realized ​ Net Realized (in thousands) From Sales Gains Losses Gain (Loss) 2024 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 41,543 ​ $ 357 ​ $ (1,139) ​ $ (782) Equity securities ​ ​ 31,473 ​ ​ 13,344 ​ ​ (340) ​ ​ 13,004 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 20,729 ​ $ 99 ​ $ (910) ​ $ (811) Equity securities ​ ​ 22,029 ​ ​ 8,841 ​ ​ (101) ​ ​ 8,740 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Calls/Maturities ​ ​ ​ ​ Gross Realized ​ Net Realized (in thousands) Proceeds Gains Losses Gain (Loss) 2024 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 158,472 ​ $ 79 ​ $ (856) ​ $ (777) 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 349,734 ​ $ 37 ​ $ (43) ​ $ (6)
Fair Value, Assets Measured on Recurring Basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of June 30, 2024 ​ ​ Quoted Prices in ​ Significant Other ​ Significant ​ ​ ​ ​ ​ Active Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ ​ ​ (in thousands) (Level 1) (Level 2) (Level 3) Total Fixed income securities - available-for-sale ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. government ​ $ — ​ $ 434,800 ​ $ — ​ $ 434,800 U.S. agency ​ ​ — ​ ​ 58,309 ​ ​ — ​ ​ 58,309 Non-U.S. government & agency ​ ​ — ​ ​ 3,828 ​ ​ — ​ ​ 3,828 Agency MBS ​ ​ — ​ ​ 414,675 ​ ​ — ​ ​ 414,675 ABS/CMBS/MBS* ​ ​ — ​ ​ 320,061 ​ ​ — ​ ​ 320,061 Corporate ​ ​ — ​ ​ 1,182,685 ​ ​ 68,095 ​ ​ 1,250,780 Municipal ​ ​ — ​ ​ 507,074 ​ ​ — ​ ​ 507,074 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,921,432 ​ $ 68,095 ​ $ 2,989,527 Equity securities ​ ​ 661,978 ​ ​ — ​ ​ 4,585 ​ ​ 666,563 Total ​ $ 661,978 ​ $ 2,921,432 ​ $ 72,680 ​ $ 3,656,090 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2023 ​ ​ Quoted Prices in ​ Significant Other ​ Significant ​ ​ ​ ​ ​ Active Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ ​ ​ (in thousands) (Level 1) (Level 2) (Level 3) Total Fixed income securities - available-for-sale ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. government ​ $ — ​ $ 308,031 ​ $ — ​ $ 308,031 U.S. agency ​ ​ — ​ ​ 59,826 ​ ​ — ​ ​ 59,826 Non-U.S. government & agency ​ ​ — ​ ​ 3,882 ​ ​ — ​ ​ 3,882 Agency MBS ​ ​ — ​ ​ 425,285 ​ ​ — ​ ​ 425,285 ABS/CMBS/MBS* ​ ​ — ​ ​ 281,182 ​ ​ — ​ ​ 281,182 Corporate ​ ​ — ​ ​ 1,164,548 ​ ​ 60,471 ​ ​ 1,225,019 Municipal ​ ​ — ​ ​ 552,624 ​ ​ — ​ ​ 552,624 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,795,378 ​ $ 60,471 ​ $ 2,855,849 Equity securities ​ ​ 588,416 ​ ​ — ​ ​ 1,625 ​ ​ 590,041 Total ​ $ 588,416 ​ $ 2,795,378 ​ $ 62,096 ​ $ 3,445,890 * Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities ​
Summary of Changes in Balance of Level 3 Securities	​ ​ ​ ​ ​ (in thousands) Level 3 Securities Balance as of January 1, 2024 ​ $ 62,096 Net realized and unrealized gains (losses) ​ ​ ​ Included in other comprehensive earnings (loss) ​ ​ (315) Purchases ​ ​ 12,310 Sales / Calls / Maturities ​ ​ (1,411) Balance as of June 30, 2024 ​ $ 72,680 Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - included in other comprehensive earnings (loss) ​ $ (315)
Schedule of Contractual Maturity of Securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2024 (in thousands) Amortized Cost Fair Value Due in one year or less ​ $ 242,522 ​ $ 239,183 Due after one year through five years ​ ​ 847,005 ​ ​ 815,300 Due after five years through 10 years ​ ​ 775,964 ​ ​ 745,887 Due after 10 years ​ ​ 548,359 ​ ​ 454,421 ABS/CMBS/MBS* ​ ​ 804,016 ​ ​ 734,736 Total available-for-sale ​ $ 3,217,866 ​ $ 2,989,527 * Asset-backed, commercial mortgage-backed and mortgage-backed securities
Schedule of Amortized Cost and Fair Value of Available-for-sale Securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2024 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 442,734 ​ $ — ​ $ 258 ​ $ (8,192) ​ $ 434,800 U.S. agency ​ ​ 60,058 ​ ​ — ​ ​ 326 ​ ​ (2,075) ​ ​ 58,309 Non-U.S. government & agency ​ ​ 4,800 ​ ​ — ​ ​ — ​ ​ (972) ​ ​ 3,828 Agency MBS ​ ​ 458,944 ​ ​ — ​ ​ 915 ​ ​ (45,184) ​ ​ 414,675 ABS/CMBS/MBS* ​ ​ 345,072 ​ ​ (2) ​ ​ 1,367 ​ ​ (26,376) ​ ​ 320,061 Corporate ​ ​ 1,310,888 ​ ​ (226) ​ ​ 3,620 ​ ​ (63,502) ​ ​ 1,250,780 Municipal ​ ​ 595,370 ​ ​ — ​ ​ 1,069 ​ ​ (89,365) ​ ​ 507,074 Total Fixed Income ​ $ 3,217,866 ​ $ (228) ​ $ 7,555 ​ $ (235,666) ​ $ 2,989,527 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2023 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 312,632 ​ $ — ​ $ 1,257 ​ $ (5,858) ​ $ 308,031 U.S. agency ​ ​ 60,763 ​ ​ — ​ ​ 652 ​ ​ (1,589) ​ ​ 59,826 Non-U.S. government & agency ​ ​ 4,800 ​ ​ — ​ ​ — ​ ​ (918) ​ ​ 3,882 Agency MBS ​ ​ 460,551 ​ ​ — ​ ​ 2,636 ​ ​ (37,902) ​ ​ 425,285 ABS/CMBS/MBS* ​ ​ 308,458 ​ ​ (3) ​ ​ 611 ​ ​ (27,884) ​ ​ 281,182 Corporate ​ ​ 1,273,187 ​ ​ (303) ​ ​ 8,766 ​ ​ (56,631) ​ ​ 1,225,019 Municipal ​ ​ 634,000 ​ ​ — ​ ​ 2,238 ​ ​ (83,614) ​ ​ 552,624 Total Fixed Income ​ $ 3,054,391 ​ $ (306) ​ $ 16,160 ​ $ (214,396) ​ $ 2,855,849 * Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities
Schedule of Debt Securities Available-for-sale Allowance for Credit Loss	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, ​ Six Months Ended June 30, (in thousands) 2024 2023 2024 2023 Beginning balance ​ $ 237 ​ $ 465 ​ $ 306 ​ $ 339 Increase to allowance from securities for which credit losses were not previously recorded ​ ​ — ​ ​ 2 ​ ​ — ​ ​ 25 Reduction from securities sold during the period ​ ​ (27) ​ ​ — ​ ​ (89) ​ ​ — Net increase (decrease) from securities that had an allowance at the beginning of the period ​ ​ 18 ​ ​ (33) ​ ​ 11 ​ ​ 70 Balance as of June 30, ​ $ 228 ​ $ 434 ​ $ 228 ​ $ 434
Schedule of Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2024 ​ December 31, 2023 (in thousands) < 12 Mos. 12 Mos. & Greater Total < 12 Mos. 12 Mos. & Greater Total U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 157,918 ​ $ 227,774 ​ $ 385,692 ​ $ 37,718 ​ $ 204,556 ​ $ 242,274 Amortized cost ​ ​ 159,088 ​ ​ 234,796 ​ ​ 393,884 ​ ​ 37,950 ​ ​ 210,182 ​ ​ 248,132 Unrealized loss ​ $ (1,170) ​ $ (7,022) ​ $ (8,192) ​ $ (232) ​ $ (5,626) ​ $ (5,858) U.S. agency ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 11,369 ​ $ 35,039 ​ $ 46,408 ​ $ 8,736 ​ $ 29,632 ​ $ 38,368 Amortized cost ​ ​ 11,507 ​ ​ 36,976 ​ ​ 48,483 ​ ​ 8,790 ​ ​ 31,167 ​ ​ 39,957 Unrealized loss ​ $ (138) ​ $ (1,937) ​ $ (2,075) ​ $ (54) ​ $ (1,535) ​ $ (1,589) Non-U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ — ​ $ 3,828 ​ $ 3,828 ​ $ — ​ $ 3,882 ​ $ 3,882 Amortized cost ​ ​ — ​ ​ 4,800 ​ ​ 4,800 ​ ​ — ​ ​ 4,800 ​ ​ 4,800 Unrealized Loss ​ $ — ​ $ (972) ​ $ (972) ​ $ — ​ $ (918) ​ $ (918) Agency MBS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 47,461 ​ $ 312,936 ​ $ 360,397 ​ $ 61,196 ​ $ 275,707 ​ $ 336,903 Amortized cost ​ ​ 47,832 ​ ​ 357,749 ​ ​ 405,581 ​ ​ 61,714 ​ ​ 313,091 ​ ​ 374,805 Unrealized loss ​ $ (371) ​ $ (44,813) ​ $ (45,184) ​ $ (518) ​ $ (37,384) ​ $ (37,902) ABS/CMBS/MBS* ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 20,533 ​ $ 178,161 ​ $ 198,694 ​ $ 12,240 ​ $ 211,436 ​ $ 223,676 Amortized cost ​ ​ 20,571 ​ ​ 204,499 ​ ​ 225,070 ​ ​ 12,367 ​ ​ 239,193 ​ ​ 251,560 Unrealized loss ​ $ (38) ​ $ (26,338) ​ $ (26,376) ​ $ (127) ​ $ (27,757) ​ $ (27,884) Corporate ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 228,328 ​ $ 801,030 ​ $ 1,029,358 ​ $ 67,402 ​ $ 822,731 ​ $ 890,133 Amortized cost ​ ​ 233,642 ​ ​ 859,218 ​ ​ 1,092,860 ​ ​ 68,345 ​ ​ 878,419 ​ ​ 946,764 Unrealized loss ​ $ (5,314) ​ $ (58,188) ​ $ (63,502) ​ $ (943) ​ $ (55,688) ​ $ (56,631) Municipal ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 54,876 ​ $ 416,438 ​ $ 471,314 ​ $ 61,218 ​ $ 391,361 ​ $ 452,579 Amortized cost ​ ​ 55,562 ​ ​ 505,117 ​ ​ 560,679 ​ ​ 61,697 ​ ​ 474,496 ​ ​ 536,193 Unrealized loss ​ $ (686) ​ $ (88,679) ​ $ (89,365) ​ $ (479) ​ $ (83,135) ​ $ (83,614) Total fixed income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 520,485 ​ $ 1,975,206 ​ $ 2,495,691 ​ $ 248,510 ​ $ 1,939,305 ​ $ 2,187,815 Amortized cost ​ ​ 528,202 ​ ​ 2,203,155 ​ ​ 2,731,357 ​ ​ 250,863 ​ ​ 2,151,348 ​ ​ 2,402,211 Unrealized loss ​ $ (7,717) ​ $ (227,949) ​ $ (235,666) ​ $ (2,353) ​ $ (212,043) ​ $ (214,396) * Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities
Schedule of Credit Quality Indicators for Investments in Unrealized Loss Positions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equivalent ​ Equivalent ​ (dollars in thousands) ​ ​ ​ NAIC S&P Moody’s ​ Amortized ​ ​ ​ ​ Unrealized ​ Percent ​ Rating Rating Rating Cost Fair Value Loss to Total ​ 1 ​ AAA/AA/A ​ Aaa/Aa/A ​ $ 2,292,580 ​ $ 2,086,894 ​ $ (205,686) ​ 87.3 % 2 ​ BBB ​ Baa ​ ​ 388,103 ​ ​ 361,830 ​ ​ (26,273) ​ 11.1 % 3 ​ BB ​ Ba ​ ​ 30,171 ​ ​ 28,674 ​ ​ (1,497) ​ 0.6 % 4 ​ B ​ B ​ ​ 16,562 ​ ​ 15,259 ​ ​ (1,303) ​ 0.6 % 5 ​ CCC ​ Caa ​ ​ 3,121 ​ ​ 2,646 ​ ​ (475) ​ 0.2 % 6 ​ CC or lower ​ Ca or lower ​ ​ 820 ​ ​ 388 ​ ​ (432) ​ 0.2 % ​ ​ ​ ​ Total ​ $ 2,731,357 ​ $ 2,495,691 ​ $ (235,666) ​ 100.0 %

Historical Loss And LAE Devel_2

Historical Loss And LAE Development (Tables)	6 Months Ended
	Jun. 30, 2024
Historical Loss And L A E Development Disclosure [Abstract]
Schedule of Reconciliation of Unpaid Losses and Settlement Expenses (LAE)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ ​ Ended June 30, (in thousands) 2024 2023 Unpaid losses and LAE at beginning of year ​ ​ ​ ​ ​ ​ Gross ​ $ 2,446,025 ​ $ 2,315,637 Ceded ​ ​ (757,349) ​ ​ (740,089) Net ​ $ 1,688,676 ​ $ 1,575,548 ​ ​ ​ ​ ​ ​ ​ Increase (decrease) in incurred losses and LAE ​ ​ ​ ​ ​ ​ Current accident year ​ $ 376,546 ​ $ 339,951 Prior accident years ​ ​ (64,923) ​ ​ (71,520) Total incurred ​ $ 311,623 ​ $ 268,431 ​ ​ ​ ​ ​ ​ ​ Loss and LAE payments for claims incurred ​ ​ ​ ​ ​ ​ Current accident year ​ $ (40,078) ​ $ (30,978) Prior accident years ​ ​ (197,887) ​ ​ (172,282) Total paid ​ $ (237,965) ​ $ (203,260) ​ ​ ​ ​ ​ ​ ​ Net unpaid losses and LAE at June 30, ​ $ 1,762,334 ​ $ 1,640,719 ​ ​ ​ ​ ​ ​ ​ Unpaid losses and LAE at June 30, ​ ​ ​ ​ ​ ​ Gross ​ $ 2,544,622 ​ $ 2,361,577 Ceded ​ ​ (782,288) ​ ​ (720,858) Net ​ $ 1,762,334 ​ $ 1,640,719

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2024
Income Tax Disclosure
Schedule of Reconciliation of Income Tax Expense Attributable to Income from Operations with Amounts Computed by Applying U.S. Federal Tax Rate to Pretax Income from Continuing Operations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months Ended June 30, ​ For the Six Months Ended June 30, 2024 ​ ​ ​ 2024 ​ 2023 ​ 2024 ​ 2023 ​ (in thousands) Amount % Amount % Amount % Amount % ​ Provision for income taxes at the statutory rate of 21% ​ $ 21,694 ​ 21.0 % $ 20,167 ​ 21.0 % $ 55,292 ​ 21.0 % $ 45,953 ​ 21.0 % Increase (reduction) in taxes resulting from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Excess tax benefit on share-based compensation ​ ​ (422) ​ (0.4) % ​ (878) ​ (0.9) % ​ (2,297) ​ (0.8) % ​ (2,868) ​ (1.3) % Tax exempt interest income ​ ​ (249) ​ (0.2) % ​ (274) ​ (0.3) % ​ (509) ​ (0.2) % ​ (557) ​ (0.3) % Dividends received deduction ​ ​ (234) ​ (0.2) % ​ (209) ​ (0.2) % ​ (468) ​ (0.2) % ​ (433) ​ (0.2) % Tax credit ​ ​ (768) ​ (0.8) % ​ (780) ​ (0.8) % ​ (1,536) ​ (0.6) % ​ (1,559) ​ (0.7) % ESOP dividends paid deduction ​ ​ (151) ​ (0.2) % ​ (144) ​ (0.2) % ​ (290) ​ (0.1) % ​ (281) ​ (0.1) % Nondeductible expenses ​ ​ 946 ​ 0.9 % ​ 745 ​ 0.8 % ​ 1,659 ​ 0.6 % ​ 1,346 ​ 0.6 % Other items, net ​ ​ 495 ​ 0.5 % ​ (248) ​ (0.3) % ​ 1,551 ​ 0.6 % ​ 758 ​ 0.4 % Total tax expense ​ $ 21,311 ​ 20.6 % $ 18,379 ​ 19.1 % $ 53,402 ​ 20.3 % $ 42,359 ​ 19.4 %

Stock Based Compensation (Table

Stock Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2024
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Option Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ Aggregate ​ ​ ​ ​ Weighted ​ Average ​ Intrinsic ​ ​ ​ ​ Average ​ Remaining ​ Value ​ Options Exercise Price Contractual Life (in 000’s) Outstanding options at January 1, 2024 ​ 1,641,710 ​ $ 92.62 ​ ​ ​ ​ ​ Options granted ​ 141,932 ​ ​ 141.73 ​ ​ ​ ​ ​ Options exercised ​ (120,940) ​ ​ 67.25 ​ ​ ​ ​ ​ Options canceled/forfeited ​ (6,900) ​ ​ 105.93 ​ ​ ​ ​ ​ Outstanding options at June 30, 2024 ​ 1,655,802 ​ $ 98.62 ​ 4.51 ​ $ 69,933 Exercisable options at June 30, 2024 ​ 983,166 ​ $ 85.13 ​ 3.39 ​ $ 54,623
Summary of Weighted Average Grant-date Assumptions and Weighted Average Fair Values	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2024 2023 ​ Weighted-average fair value of grants ​ $ 31.09 ​ $ 26.79 ​ Risk-free interest rates ​ ​ 4.91 % ​ 3.44 % Dividend yield ​ ​ 2.30 % ​ 2.29 % Expected volatility ​ ​ 23.08 % ​ 22.95 % Expected option life ​ ​ 5.00 years ​ 4.94 years
Schedule of Restricted Stock Units Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ RSUs Fair Value Nonvested at January 1, 2024 ​ 45,093 ​ $ 125.16 Granted ​ 19,531 ​ ​ 142.83 Reinvested ​ 179 ​ ​ 143.82 Vested ​ (17,198) ​ ​ 122.96 Forfeited ​ (606) ​ ​ 132.42 Nonvested at June 30, 2024 ​ 46,999 ​ $ 133.29 ​

Operating Segment Information (

Operating Segment Information (Tables)	6 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Summary of Selected Information by Operating Segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months Revenues ​ Ended June 30, ​ Ended June 30, (in thousands) 2024 2023 2024 2023 Casualty ​ $ 209,100 ​ $ 187,048 ​ $ 407,376 ​ $ 373,079 Property ​ ​ 134,097 ​ ​ 101,841 ​ ​ 263,508 ​ ​ 190,608 Surety ​ ​ 35,868 ​ ​ 33,391 ​ ​ 68,857 ​ ​ 66,316 Net premiums earned ​ $ 379,065 ​ $ 322,280 ​ $ 739,741 ​ $ 630,003 Net investment income ​ ​ 33,961 ​ ​ 28,788 ​ ​ 66,808 ​ ​ 55,872 Net realized gains (losses) ​ ​ (192) ​ ​ 5,580 ​ ​ 5,802 ​ ​ 20,200 Net unrealized gains on equity securities ​ ​ 3,608 ​ ​ 25,214 ​ ​ 48,922 ​ ​ 40,710 Total consolidated revenue ​ $ 416,442 ​ $ 381,862 ​ $ 861,273 ​ $ 746,785 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Earnings ​ ​ ​ ​ ​ ​ (in thousands) 2024 2023 2024 2023 Casualty ​ $ 10,315 ​ $ 6,977 ​ $ 23,989 ​ $ 38,808 Property ​ ​ 53,180 ​ ​ 25,877 ​ ​ 110,896 ​ ​ 54,260 Surety ​ ​ 6,529 ​ ​ 8,347 ​ ​ 12,834 ​ ​ 16,023 Net underwriting income ​ $ 70,024 ​ $ 41,201 ​ $ 147,719 ​ $ 109,091 Net investment income ​ ​ 33,961 ​ ​ 28,788 ​ ​ 66,808 ​ ​ 55,872 Net realized gains (losses) ​ ​ (192) ​ ​ 5,580 ​ ​ 5,802 ​ ​ 20,200 Net unrealized gains on equity securities ​ ​ 3,608 ​ ​ 25,214 ​ ​ 48,922 ​ ​ 40,710 General corporate expense and interest on debt ​ ​ (5,744) ​ ​ (6,266) ​ ​ (12,372) ​ ​ (12,488) Equity in earnings of unconsolidated investees ​ ​ 1,646 ​ ​ 1,514 ​ ​ 6,415 ​ ​ 5,437 Earnings before income taxes ​ $ 103,303 ​ $ 96,031 ​ $ 263,294 ​ $ 218,822 Income tax expense ​ ​ 21,311 ​ ​ 18,379 ​ ​ 53,402 ​ ​ 42,359 Net earnings ​ $ 81,992 ​ $ 77,652 ​ $ 209,892 ​ $ 176,463
Summary of Revenue by Major Product Type	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months Net Premiums Earned ​ Ended June 30, ​ Ended June 30, (in thousands) 2024 2023 2024 2023 Casualty ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial excess and personal umbrella ​ $ 85,986 ​ $ 69,261 ​ $ 166,021 ​ $ 136,843 Commercial transportation ​ ​ 29,323 ​ ​ 25,398 ​ ​ 56,624 ​ ​ 50,630 General liability ​ ​ 26,104 ​ ​ 26,016 ​ ​ 51,516 ​ ​ 51,916 Professional services ​ ​ 26,000 ​ ​ 24,602 ​ ​ 51,085 ​ ​ 48,959 Small commercial ​ ​ 19,459 ​ ​ 18,455 ​ ​ 37,796 ​ ​ 36,396 Executive products ​ ​ 5,448 ​ ​ 6,153 ​ ​ 11,363 ​ ​ 12,506 Other casualty ​ ​ 16,780 ​ ​ 17,163 ​ ​ 32,971 ​ ​ 35,829 Total ​ $ 209,100 ​ $ 187,048 ​ $ 407,376 ​ $ 373,079 Property ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial property ​ $ 87,400 ​ $ 60,219 ​ $ 175,005 ​ $ 109,481 Marine ​ ​ 37,069 ​ ​ 32,412 ​ ​ 69,637 ​ ​ 63,048 Other property ​ ​ 9,628 ​ ​ 9,210 ​ ​ 18,866 ​ ​ 18,079 Total ​ $ 134,097 ​ $ 101,841 ​ $ 263,508 ​ $ 190,608 Surety ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Transactional ​ $ 12,308 ​ $ 11,887 ​ $ 24,416 ​ $ 23,934 Commercial ​ ​ 12,700 ​ ​ 12,505 ​ ​ 23,325 ​ ​ 24,923 Contract ​ ​ 10,860 ​ ​ 8,999 ​ ​ 21,116 ​ ​ 17,459 Total ​ $ 35,868 ​ $ 33,391 ​ $ 68,857 ​ $ 66,316 Grand Total ​ $ 379,065 ​ $ 322,280 ​ $ 739,741 ​ $ 630,003 ​

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2024
Leases [Abstract]
Schedule of Components of Lease Expense and Other lease Information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months ​ ​ Ended June 30, ​ Ended June 30, (in thousands) 2024 2023 2024 2023 Operating lease cost ​ $ 1,153 ​ $ 1,239 ​ $ 2,334 ​ $ 2,508 Variable lease cost ​ ​ 260 ​ ​ 444 ​ ​ 508 ​ ​ 882 Sublease income ​ ​ (42) ​ ​ (139) ​ ​ (85) ​ ​ (277) Total lease cost ​ $ 1,371 ​ $ 1,544 ​ $ 2,757 ​ $ 3,113 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash paid for amounts included in measurement of lease liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating cash outflows from operating leases ​ $ 1,105 ​ $ 1,357 ​ $ 2,168 ​ $ 2,755 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ 333 ​ $ 943 ​ $ 3,789 ​ $ 984 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reduction to ROU assets resulting from reduction to lease liabilities ​ $ — ​ $ — ​ $ — ​ $ 200 ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) June 30, 2024 December 31, 2023 ​ Operating lease ROU assets ​ $ 15,417 ​ $ 13,666 ​ Operating lease liabilities ​ $ 16,783 ​ $ 14,880 ​ Weighted-average remaining lease term - operating leases ​ ​ 6.14 years ​ 6.08 years Weighted-average discount rate - operating leases ​ ​ 3.56 % ​ 3.21 % ​
Schedule of Future Minimum Lease Payments under Non-cancellable Leases	​ ​ ​ ​ ​ (in thousands) June 30, 2024 2024 ​ $ 1,994 2025 ​ ​ 4,197 2026 ​ ​ 3,473 2027 ​ ​ 2,107 2028 ​ ​ 1,537 2029 ​ ​ 1,443 Thereafter ​ ​ 4,489 Total future minimum lease payments ​ $ 19,240 Less imputed interest ​ ​ (2,457) Total operating lease liability ​ $ 16,783 ​

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies - Reinsurance - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Reinsurance
Amount of allowance for uncollectible amounts on paid recoverables	$ 16,000,000	$ 16,000,000
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	11,025,000	$ 10,608,000
Financing receivable, allowance for credit Loss, write-off	0
Maximum
Reinsurance
Financing receivable, allowance for credit loss, recovery	$ 1,000,000

Basis of Presentation and Sum_5

Basis of Presentation and Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details) - USD ($)	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Business Acquisition
Goodwill	$ 46,062,000	$ 46,062,000
Indefinite-lived intangibles	7,500,000	7,500,000
Total goodwill and intangibles	53,562,000	53,562,000
Goodwill and intangible asset impairment	0
Surety
Business Acquisition
Goodwill	40,816,000	40,816,000
Casualty
Business Acquisition
Goodwill	$ 5,246,000	$ 5,246,000

Summary of Significant Accounti

Summary of Significant Accounting Policies - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Basic EPS, Income (Numerator)
Income available to common shareholders	$ 81,992	$ 77,652	$ 209,892	$ 176,463
Diluted EPS, Income (Numerator)
Income available to common shareholders	$ 81,992	$ 77,652	$ 209,892	$ 176,463
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	45,737	45,591	45,709	45,560
Effect of Dilutive Securities, Shares (Denominator)
Stock options and restricted stock units	442	453	460	485
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	46,179	46,044	46,169	46,045
Earnings Per Share, Diluted, Other Disclosures
Anti-dilutive securities excluded from diluted EPS		118	114	118
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)	$ 1.79	$ 1.70	$ 4.59	$ 3.87
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.78	$ 1.69	$ 4.55	$ 3.83

Basis of Presentation and Sum_6

Basis of Presentation and Summary of Significant Accounting Policies - Comprehensive Earnings (Loss) - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
COMPREHENSIVE EARNINGS (LOSS)
Tax rate used (as a percent)	21%		21%		21%	21%
Other comprehensive earnings (loss), tax (benefit)	$ (2,000)		$ (5,000)		$ (5,000)	$ 5,000
Other comprehensive earnings (loss), net of tax	$ (7,843)	$ (12,671)	$ (19,721)	$ 37,707	$ (20,514)	$ 17,986

Summary of Significant Accoun_2

Summary of Significant Accounting Policies - Changes in the Balance of Each Component of Accumulated Other Comprehensive Earnings (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Beginning balance		$ (166,303)			$ (166,303)
Other comprehensive earnings (loss)	$ (7,843)	(12,671)	$ (19,721)	$ 37,707	(20,514)	$ 17,986
Ending balance	(186,817)				(186,817)
Unrealized Gains and Losses on Available-for-Sale Securities
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Beginning balance	(178,974)	(166,303)	(191,369)	(229,076)	(166,303)	(229,076)
Other comprehensive earnings (loss) before reclassifications	(8,571)		(20,347)		(21,846)	15,908
Amounts reclassified from accumulated other comprehensive earnings	728		626		1,332	2,078
Other comprehensive earnings (loss)	(7,843)		(19,721)		(20,514)	17,986
Ending balance	(186,817)	$ (178,974)	(211,090)	$ (191,369)	(186,817)	(211,090)
Balance of securities for which an allowance for credit losses has been recognized in net earnings	$ 1,463		$ 1,053		$ 1,463	$ 1,053

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss)
Earnings (loss) before income taxes	$ 103,303		$ 96,031		$ 263,294	$ 218,822
Income tax (expense) benefit	(21,311)		(18,379)		(53,402)	(42,359)
Net earnings (loss)	81,992	$ 127,900	77,652	$ 98,811	209,892	176,463
Unrealized Gains and Losses on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss)
Net realized gains (losses) - Available-for-sale	(931)		(824)		(1,765)	(2,536)
Credit gains (losses) presented within net realized gains	9		31		79	(95)
Earnings (loss) before income taxes	(922)		(793)		(1,686)	(2,631)
Income tax (expense) benefit	194		167		354	553
Net earnings (loss)	$ (728)		$ (626)		$ (1,332)	$ (2,078)

Investments - Disposition of Fi

Investments - Disposition of Fixed Income and Equity Securities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Summary of the disposition of fixed income and equity securities
Fixed income securities - available-for-sale	$ 41,543	$ 19,490
Fixed income securities - available-for-sale	159,869	349,714
Net Realized Gain (Loss) - Fixed income securities - available-for-sale	0	(2,000)
SALES
Summary of the disposition of fixed income and equity securities
Fixed income securities - available-for-sale	41,543	20,729
Gross Realized Gains - Fixed income securities - available-for-sale	357	99
Gross Realized Losses - Fixed income securities - available-for-sale	(1,139)	(910)
Net Realized Gain (Loss) - Fixed income securities - available-for-sale	(782)	(811)
Proceeds from Sales - Equity securities	31,473	22,029
Gross Realized Gains - Equity securities	13,344	8,841
Gross Realized Losses - Equity securities	(340)	(101)
Net Realized Gain (Loss) - Equity securities	13,004	8,740
Calls And Maturities Of Marketable Securities
Summary of the disposition of fixed income and equity securities
Fixed income securities - available-for-sale	158,472	349,734
Gross Realized Gains - Fixed income securities - available-for-sale	79	37
Gross Realized Losses - Fixed income securities - available-for-sale	(856)	(43)
Net Realized Gain (Loss) - Fixed income securities - available-for-sale	$ (777)	$ (6)

Investments - Assets Measured a

Investments - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Assets measured at Fair Value
Available-for-sale fixed income	$ 2,989,527	$ 2,855,849
Equity securities	666,563	590,041
U.S. government
Assets measured at Fair Value
Available-for-sale fixed income	434,800	308,031
U.S. Agency
Assets measured at Fair Value
Available-for-sale fixed income	58,309	59,826
Non-U.S. government & agency
Assets measured at Fair Value
Available-for-sale fixed income	3,828	3,882
Agency MBS
Assets measured at Fair Value
Available-for-sale fixed income	414,675	425,285
ABS/CMBS/MBS
Assets measured at Fair Value
Available-for-sale fixed income	320,061	281,182
Corporate Debt
Assets measured at Fair Value
Available-for-sale fixed income	1,250,780	1,225,019
Municipal
Assets measured at Fair Value
Available-for-sale fixed income	507,074	552,624
Fair Value Measured on Recurring Basis
Assets measured at Fair Value
Available-for-sale fixed income	2,989,527	2,855,849
Equity securities	666,563	590,041
Total assets at fair value	3,656,090	3,445,890
Fair Value Measured on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets measured at Fair Value
Equity securities	661,978	588,416
Total assets at fair value	661,978	588,416
Fair Value Measured on Recurring Basis | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	2,921,432	2,795,378
Total assets at fair value	2,921,432	2,795,378
Fair Value Measured on Recurring Basis | Significant Unobservable Inputs (Level 3)
Assets measured at Fair Value
Available-for-sale fixed income	68,095	60,471
Equity securities	4,585	1,625
Total assets at fair value	72,680	62,096
Fair Value Measured on Recurring Basis | U.S. government
Assets measured at Fair Value
Available-for-sale fixed income	434,800	308,031
Fair Value Measured on Recurring Basis | U.S. government | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	434,800	308,031
Fair Value Measured on Recurring Basis | U.S. Agency
Assets measured at Fair Value
Available-for-sale fixed income	58,309	59,826
Fair Value Measured on Recurring Basis | U.S. Agency | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	58,309	59,826
Fair Value Measured on Recurring Basis | Non-U.S. government & agency
Assets measured at Fair Value
Available-for-sale fixed income	3,828	3,882
Fair Value Measured on Recurring Basis | Non-U.S. government & agency | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	3,828	3,882
Fair Value Measured on Recurring Basis | Agency MBS
Assets measured at Fair Value
Available-for-sale fixed income	414,675	425,285
Fair Value Measured on Recurring Basis | Agency MBS | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	414,675	425,285
Fair Value Measured on Recurring Basis | ABS/CMBS/MBS
Assets measured at Fair Value
Available-for-sale fixed income	320,061	281,182
Fair Value Measured on Recurring Basis | ABS/CMBS/MBS | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	320,061	281,182
Fair Value Measured on Recurring Basis | Corporate Debt
Assets measured at Fair Value
Available-for-sale fixed income	1,250,780	1,225,019
Fair Value Measured on Recurring Basis | Corporate Debt | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	1,182,685	1,164,548
Fair Value Measured on Recurring Basis | Corporate Debt | Significant Unobservable Inputs (Level 3)
Assets measured at Fair Value
Available-for-sale fixed income	68,095	60,471
Fair Value Measured on Recurring Basis | Municipal
Assets measured at Fair Value
Available-for-sale fixed income	507,074	552,624
Fair Value Measured on Recurring Basis | Municipal | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	$ 507,074	$ 552,624

Investments - Changes in Balanc

Investments - Changes in Balance of Level 3 Securities (Details) - Significant Unobservable Inputs (Level 3) $ in Thousands	6 Months Ended
	Jun. 30, 2024 USD ($)
Summary of changes in Level 3 securities
Beginning balance	$ 62,096
Included in other comprehensive earnings (loss)	(315)
Purchases	12,310
Sales / Calls / Maturities	(1,411)
Ending balance	72,680
Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - OCI	$ (315)

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 242,522
Due after one year through five years	847,005
Due after five years through 10 years	775,964
Due after 10 years	548,359
ABS/CMBS/MBS	804,016
Total available-for-sale	3,217,866	$ 3,054,391
Fair Value
Due in one year or less	239,183
Due after one year through five years	815,300
Due after five years through 10 years	745,887
Due after 10 years	454,421
ABS/CMBS/MBS	734,736
Total available-for-sale	$ 2,989,527	$ 2,855,849

Investments - Additional Inform

Investments - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2024 USD ($) security	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Investments
Accrued investment income | $	$ 26,683		$ 24,062
Number of debt securities for which there is an allowance for credit losses | security	9
Losses on fixed income securities | $	$ 0	$ 2,000
Number of debt securities in an unrealized loss position for which an allowance for credit losses has not been recorded | security	1,366
Unrealized loss | $	$ 235,666		214,396
Unrealized losses as percentage of fixed income portfolio cost basis	7%
Unrealized losses relative to total invested assets (as a percent)	6%
Number of unrealized loss positions | security	1,366
Number of securities in unrealized loss positions for 12 months or longer | security	1,156
Fixed Income Securities
Investments
Accrued investment income | $	$ 26,000		$ 23,000

Investments - Amortized Cost _2

Investments - Amortized Cost and Fair Value of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Available For Sale Securities
Cost or Amortized Cost	$ 3,217,866		$ 3,054,391
Allowance for Credit Losses	(228)	$ (237)	(306)	$ (434)	$ (465)	$ (339)
Gross Unrealized Gains	7,555		16,160
Gross Unrealized Losses	(235,666)		(214,396)
Fair Value	2,989,527		2,855,849
U.S. government
Available For Sale Securities
Cost or Amortized Cost	442,734		312,632
Gross Unrealized Gains	258		1,257
Gross Unrealized Losses	(8,192)		(5,858)
Fair Value	434,800		308,031
U.S. Agency
Available For Sale Securities
Cost or Amortized Cost	60,058		60,763
Gross Unrealized Gains	326		652
Gross Unrealized Losses	(2,075)		(1,589)
Fair Value	58,309		59,826
Non-U.S. government & agency
Available For Sale Securities
Cost or Amortized Cost	4,800		4,800
Gross Unrealized Losses	(972)		(918)
Fair Value	3,828		3,882
Agency MBS
Available For Sale Securities
Cost or Amortized Cost	458,944		460,551
Gross Unrealized Gains	915		2,636
Gross Unrealized Losses	(45,184)		(37,902)
Fair Value	414,675		425,285
ABS/CMBS/MBS
Available For Sale Securities
Cost or Amortized Cost	345,072		308,458
Allowance for Credit Losses	(2)		(3)
Gross Unrealized Gains	1,367		611
Gross Unrealized Losses	(26,376)		(27,884)
Fair Value	320,061		281,182
Corporate Debt
Available For Sale Securities
Cost or Amortized Cost	1,310,888		1,273,187
Allowance for Credit Losses	(226)		(303)
Gross Unrealized Gains	3,620		8,766
Gross Unrealized Losses	(63,502)		(56,631)
Fair Value	1,250,780		1,225,019
Municipal
Available For Sale Securities
Cost or Amortized Cost	595,370		634,000
Gross Unrealized Gains	1,069		2,238
Gross Unrealized Losses	(89,365)		(83,614)
Fair Value	$ 507,074		$ 552,624

Investments - Debt Securities A

Investments - Debt Securities Available-for-sale Allowance for Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Investments Debt And Equity Securities [Abstract]
Beginning balance	$ 237	$ 465	$ 306	$ 339
Increase to allowance from securities for which credit losses were not previously recorded		2		25
Reduction from securities sold during the period	(27)		(89)
Net increase (decrease) from securities that had an allowance at the beginning of the period	18	(33)	11	70
Ending balance	$ 228	$ 434	$ 228	$ 434

Investments - Securities in an

Investments - Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair value
Less than 12 months	$ 520,485	$ 248,510
12 months and greater	1,975,206	1,939,305
Total Fair Value	2,495,691	2,187,815
Amortized Cost
Amortized cost, less than 12 months	528,202	250,863
12 months and greater	2,203,155	2,151,348
Total Cost or Amortized Cost	2,731,357	2,402,211
Unrealized Loss
Less than 12 months	(7,717)	(2,353)
12 months and greater	(227,949)	(212,043)
Total Unrealized Loss	(235,666)	(214,396)
U.S. government
Fair value
Less than 12 months	157,918	37,718
12 months and greater	227,774	204,556
Total Fair Value	385,692	242,274
Amortized Cost
Amortized cost, less than 12 months	159,088	37,950
12 months and greater	234,796	210,182
Total Cost or Amortized Cost	393,884	248,132
Unrealized Loss
Less than 12 months	(1,170)	(232)
12 months and greater	(7,022)	(5,626)
Total Unrealized Loss	(8,192)	(5,858)
U.S. Agency
Fair value
Less than 12 months	11,369	8,736
12 months and greater	35,039	29,632
Total Fair Value	46,408	38,368
Amortized Cost
Amortized cost, less than 12 months	11,507	8,790
12 months and greater	36,976	31,167
Total Cost or Amortized Cost	48,483	39,957
Unrealized Loss
Less than 12 months	(138)	(54)
12 months and greater	(1,937)	(1,535)
Total Unrealized Loss	(2,075)	(1,589)
Non-U.S. government & agency
Fair value
12 months and greater	3,828	3,882
Total Fair Value	3,828	3,882
Amortized Cost
12 months and greater	4,800	4,800
Total Cost or Amortized Cost	4,800	4,800
Unrealized Loss
12 months and greater	(972)	(918)
Total Unrealized Loss	(972)	(918)
Agency MBS
Fair value
Less than 12 months	47,461	61,196
12 months and greater	312,936	275,707
Total Fair Value	360,397	336,903
Amortized Cost
Amortized cost, less than 12 months	47,832	61,714
12 months and greater	357,749	313,091
Total Cost or Amortized Cost	405,581	374,805
Unrealized Loss
Less than 12 months	(371)	(518)
12 months and greater	(44,813)	(37,384)
Total Unrealized Loss	(45,184)	(37,902)
ABS/CMBS/MBS
Fair value
Less than 12 months	20,533	12,240
12 months and greater	178,161	211,436
Total Fair Value	198,694	223,676
Amortized Cost
Amortized cost, less than 12 months	20,571	12,367
12 months and greater	204,499	239,193
Total Cost or Amortized Cost	225,070	251,560
Unrealized Loss
Less than 12 months	(38)	(127)
12 months and greater	(26,338)	(27,757)
Total Unrealized Loss	(26,376)	(27,884)
Corporate Debt
Fair value
Less than 12 months	228,328	67,402
12 months and greater	801,030	822,731
Total Fair Value	1,029,358	890,133
Amortized Cost
Amortized cost, less than 12 months	233,642	68,345
12 months and greater	859,218	878,419
Total Cost or Amortized Cost	1,092,860	946,764
Unrealized Loss
Less than 12 months	(5,314)	(943)
12 months and greater	(58,188)	(55,688)
Total Unrealized Loss	(63,502)	(56,631)
Municipal
Fair value
Less than 12 months	54,876	61,218
12 months and greater	416,438	391,361
Total Fair Value	471,314	452,579
Amortized Cost
Amortized cost, less than 12 months	55,562	61,697
12 months and greater	505,117	474,496
Total Cost or Amortized Cost	560,679	536,193
Unrealized Loss
Less than 12 months	(686)	(479)
12 months and greater	(88,679)	(83,135)
Total Unrealized Loss	$ (89,365)	$ (83,614)

Investments - Unrealized Losses

Investments - Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,731,357	$ 2,402,211
Fair value
Total Fair Value	2,495,691	2,187,815
Unrealized Loss
Total Unrealized Loss	$ (235,666)	$ (214,396)
Percent to Total	100%
NAIC Rating 1 | AAA/AA/A | Aaa/Aa/A
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,292,580
Fair value
Total Fair Value	2,086,894
Unrealized Loss
Total Unrealized Loss	$ (205,686)
Percent to Total	87.30%
NAIC Rating 2 | BBB | Baa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 388,103
Fair value
Total Fair Value	361,830
Unrealized Loss
Total Unrealized Loss	$ (26,273)
Percent to Total	11.10%
NAIC Rating 3 | BB | Ba
Cost or amortized Cost
Total Cost or Amortized Cost	$ 30,171
Fair value
Total Fair Value	28,674
Unrealized Loss
Total Unrealized Loss	$ (1,497)
Percent to Total	0.60%
NAIC Rating 4 | B | B
Cost or amortized Cost
Total Cost or Amortized Cost	$ 16,562
Fair value
Total Fair Value	15,259
Unrealized Loss
Total Unrealized Loss	$ (1,303)
Percent to Total	0.60%
NAIC Rating 5 | CCC | Caa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 3,121
Fair value
Total Fair Value	2,646
Unrealized Loss
Total Unrealized Loss	$ (475)
Percent to Total	0.20%
NAIC Rating 6 | CC Or Lower | Ca or lower
Cost or amortized Cost
Total Cost or Amortized Cost	$ 820
Fair value
Total Fair Value	388
Unrealized Loss
Total Unrealized Loss	$ (432)
Percent to Total	0.20%

Investments - Debt and Short-te

Investments - Debt and Short-term Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Investments
Other investments	$ 55,364		$ 55,364		$ 59,081
Investment in unconsolidated investees	67,249		67,249		56,966
Cash and Short-term Investments
Cash	50,030		50,030		36,424
Short-term investments	125,865		125,865		134,923
Other Unconsolidated Investees | Maximum
Investments
Investment in unconsolidated investees	1,000		1,000
Prime Holdings Insurance Services, Inc. (Prime)
Investments
Investment in unconsolidated investees	67,000		67,000
FHLBC
Investments
Investments pledged as collateral	$ 57,000		$ 57,000
Investment in federal home loan bank stock	us-gaap:AssetPledgedAsCollateralMember		us-gaap:AssetPledgedAsCollateralMember
Federal home loan bank borrowings fair value disclosure	$ 50,000		$ 50,000
Investment In Low Income Housing Tax Credit Partnerships (LIHTC)
Investments
Other investments	9,000		9,000		10,000
Amortization on low income housing investments	$ 1,000	$ 1,000	$ 1,000	$ 2,000
Amortization of tax credit partnerships, Statement of Income	Income tax expense	Income tax expense	Income tax expense	Income tax expense
Total tax benefit on investments in tax credit partnership	$ 1,000	$ 1,000	$ 1,000	$ 2,000
Investment In Low Income Housing Tax Credit Partnerships (LIHTC) | Maximum
Investments
Qualified affordable housing project investments, unfunded commitment	1,000		1,000
Historic tax credit partnerships (HTC)
Investments
Other investments	11,000		11,000		13,000
Amortization on qualifying equity investments	$ 1,000	$ 1,000	$ 2,000	$ 2,000
Amortization of tax credit partnerships, Statement of Income	Income tax expense	Income tax expense	Income tax expense	Income tax expense
Total tax benefit on investments in tax credit partnership	$ 1,000	$ 1,000	$ 3,000	$ 3,000
Investment in Private Funds
Investments
Other investments	25,000		25,000		$ 28,000
Fair value investments entities that calculate net asset value per share, unfunded commitments	$ 4,000		$ 4,000

Historical Loss and LAE Devel_3

Historical Loss and LAE Development - Reconciliation of Unpaid Losses and Settlement Expenses (LAE) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Unpaid losses and LAE at beginning of year
Gross	$ 2,446,025	$ 2,315,637
Ceded	(757,349)	(740,089)
Net	1,688,676	1,575,548
Increase (decrease) in incurred losses and LAE
Current accident year	376,546	339,951
Prior accident years	(64,923)	(71,520)
Total incurred	311,623	268,431
Loss and LAE payments for claims incurred
Current accident year	(40,078)	(30,978)
Prior accident years	(197,887)	(172,282)
Total paid	(237,965)	(203,260)
Net unpaid losses and LAE at June 30	1,762,334	1,640,719
Unpaid losses and LAE at June 30
Gross	2,544,622	2,361,577
Ceded	(782,288)	(720,858)
Net unpaid losses and LAE at June 30	$ 1,762,334	$ 1,640,719

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Tax Disclosure
Effective income tax rate reconciliation, percent, total	20.60%	19.10%	20.30%	19.40%
U.S. federal tax rate	21%	21%	21%	21%

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Expense (Benefit) Attributable to Income from Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reconciliation of income tax expense reported to amount computed by applying the U.S. federal tax rate
Provision for income taxes at the statutory federal rate	$ 21,694	$ 20,167	$ 55,292	$ 45,953
Increase (reduction) in taxes resulting from:
Excess tax benefit on share-based compensation	(422)	(878)	(2,297)	(2,868)
Tax exempt interest income	(249)	(274)	(509)	(557)
Dividends received deduction	(234)	(209)	(468)	(433)
Tax credit	(768)	(780)	(1,536)	(1,559)
ESOP dividends paid deduction	(151)	(144)	(290)	(281)
Nondeductible expenses	946	745	1,659	1,346
Other items, net	495	(248)	1,551	758
Income tax expense	$ 21,311	$ 18,379	$ 53,402	$ 42,359
Reconciliation of income tax expense rate to the U.S. federal tax rate
Tax rate used (as a percent)	21%	21%	21%	21%
Excess tax benefit on share-based compensation (as a percent)	(0.40%)	(0.90%)	(0.80%)	(1.30%)
Effective rate reduction due to tax exempt interest income (as a percent)	(0.20%)	(0.30%)	(0.20%)	(0.30%)
Effective rate reduction due to dividend received (as a percent)	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Effective rate reduction due to tax credit (as a percent)	(0.80%)	(0.80%)	(0.60%)	(0.70%)
Effective rate reduction due to dividend paid to ESOP (as a percent)	(0.20%)	(0.20%)	(0.10%)	(0.10%)
Effective rate reduction due to nondeductible expenses (as a percent)	0.90%	0.80%	0.60%	0.60%
Effective rate reduction due to other items, net (as a percent)	0.50%	(0.30%)	0.60%	0.40%
Total tax expense (as a percent)	20.60%	19.10%	20.30%	19.40%

Stock Based Compensation - Stoc

Stock Based Compensation - Stock Plans - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		14 Months Ended	96 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	May 03, 2023	May 04, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options granted (in shares)			141,932
Intrinsic value of options			$ 9	$ 16
RLI Corp. Long-Term Incentive Plans
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Stock-based compensation expenses	$ 2.2	$ 2.2	4	4.7
Income tax benefit from stock-based compensation	0.3	$ 0.3	0.6	$ 0.8
Unrecognized stock-based compensation expense	$ 9		$ 9		$ 9
Stock-based compensation expenses, recognition period			2 years 8 months 26 days
RLI Corp. Long-Term Incentive Plans | Employee Stock Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period			5 years
Term of options			8 years
RLI Corp. Long-Term Incentive Plans | Employee Stock Option | Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Age and period of service of the participant to be eligible for retirement			75 years
RLI Corp. Long-Term Incentive Plan (2015 LTIP)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares authorized for grant						4,000,000
Options granted (in shares)						3,291,388
RLI Corp. Long-Term Incentive Plan (2023 LTIP)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares authorized for grant							4,004,891
Options granted (in shares)			161,463		357,001

Stock Based Compensation - Summ

Stock Based Compensation - Summary of Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2024 USD ($) $ / shares shares	Jun. 30, 2023 USD ($)
Weighted Number of Options Outstanding
Outstanding options, Beginning Balance | shares	1,641,710
Options granted (in shares) | shares	141,932
Options exercised | shares	(120,940)
Options canceled/forfeited | shares	(6,900)
Outstanding options, Ending Balance | shares	1,655,802
Exercisable options, Ending Balance | shares	983,166
Weighted Average Exercise Price
Weighted Average Exercise Price, Outstanding options, Beginning Balance | $ / shares	$ 92.62
Weighted Average Exercise Price, Options granted | $ / shares	141.73
Weighted Average Exercise Price, Options exercised | $ / shares	67.25
Weighted Average Exercise Price, Options canceled/forfeited | $ / shares	105.93
Weighted Average Exercise Price, Outstanding options, Ending Balance | $ / shares	98.62
Weighted Average Exercise Price, Exercisable options | $ / shares	$ 85.13
Weighted Average Remaining Contractual Life
Weighted Average Remaining Contractual Life, Outstanding options	4 years 6 months 3 days
Weighted Average Remaining Contractual Life, Exercisable options	3 years 4 months 20 days
Aggregate Intrinsic Value, Options exercised | $	$ 9,000	$ 16,000
Aggregate Intrinsic Value, Outstanding options | $	69,933
Aggregate Intrinsic Value, Exercisable options | $	$ 54,623

Stock Based Compensation - Su_2

Stock Based Compensation - Summary of Weighted Average Grant-date Assumptions and Weighted Average Fair Values (Details) - $ / shares	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Weighted average grant date assumptions and weighted average fair value
Weighted-average fair value of grants	$ 31.09	$ 26.79
Risk-free interest rates	4.91%	3.44%
Dividend yield	2.30%	2.29%
Expected volatility	23.08%	22.95%
Expected option life	5 years	4 years 11 months 8 days

Stock Based Compensation - Rest

Stock Based Compensation - Restricted Stock Units - Additional Information (Details) - Restricted Stock Units (RSUs) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Share Based Compensation
Fair value of restricted stock units vested	$ 2	$ 1
Minimum
Share Based Compensation
Age and period of service of the participant to be eligible for retirement	75 years
Employees
Share Based Compensation
Award vesting period	3 years
Directors
Share Based Compensation
Award vesting period	1 year

Stock Based Compensation - Sche

Stock Based Compensation - Schedule of Restricted Stock Units Activity (Details)	6 Months Ended
	Jun. 30, 2024 $ / shares shares
Number of RSUs
RSUs Nonvested, Beginning Balance | shares	45,093
RSUs Granted | shares	19,531
RSUs Reinvested | shares	179
RSUs Vested | shares	(17,198)
RSUs Forfeited | shares	(606)
RSUs Nonvested, Ending Balance | shares	46,999
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested, Beginning Balance | $ / shares	$ 125.16
Weighted Average Grant Date Fair Value, Granted | $ / shares	142.83
Weighted Average Grant Date Fair Value, Reinvested | $ / shares	143.82
Weighted Average Grant Date Fair Value, Vested | $ / shares	122.96
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	132.42
Weighted Average Grant Date Fair Value, Nonvested, Ending Balance | $ / shares	$ 133.29

Operating Segment Information -

Operating Segment Information - Summary by Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues
Net premiums earned	$ 379,065		$ 322,280		$ 739,741	$ 630,003
Net investment income	33,961		28,788		66,808	55,872
Net realized gains (losses)	(192)		5,580		5,802	20,200
Net unrealized gains on equity securities	3,608		25,214		48,922	40,710
Consolidated revenue	416,442		381,862		861,273	746,785
Net Earnings
Net underwriting income	70,024		41,201		147,719	109,091
Net investment income	33,961		28,788		66,808	55,872
Net realized gains (losses)	(192)		5,580		5,802	20,200
Net unrealized gains on equity securities	3,608		25,214		48,922	40,710
General corporate expense and interest on debt	(5,744)		(6,266)		(12,372)	(12,488)
Equity in earnings of unconsolidated investees	1,646		1,514		6,415	5,437
Earnings (loss) before income taxes	103,303		96,031		263,294	218,822
Income tax expense	21,311		18,379		53,402	42,359
Net earnings (loss)	81,992	$ 127,900	77,652	$ 98,811	209,892	176,463
Casualty Segment
Revenues
Net premiums earned	209,100		187,048		407,376	373,079
Net Earnings
Net underwriting income	10,315		6,977		23,989	38,808
Property Segment
Revenues
Net premiums earned	134,097		101,841		263,508	190,608
Net Earnings
Net underwriting income	53,180		25,877		110,896	54,260
Surety Segment
Revenues
Net premiums earned	35,868		33,391		68,857	66,316
Net Earnings
Net underwriting income	$ 6,529		$ 8,347		$ 12,834	$ 16,023

Operating Segment Information_2

Operating Segment Information - Summary of Revenue by Major Product Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting
Net premiums earned	$ 379,065	$ 322,280	$ 739,741	$ 630,003
Casualty Segment
Segment Reporting
Net premiums earned	209,100	187,048	407,376	373,079
Casualty Segment | Commercial excess and personal umbrella
Segment Reporting
Net premiums earned	85,986	69,261	166,021	136,843
Casualty Segment | Commercial transportation
Segment Reporting
Net premiums earned	29,323	25,398	56,624	50,630
Casualty Segment | General liability
Segment Reporting
Net premiums earned	26,104	26,016	51,516	51,916
Casualty Segment | Professional services
Segment Reporting
Net premiums earned	26,000	24,602	51,085	48,959
Casualty Segment | Small commercial
Segment Reporting
Net premiums earned	19,459	18,455	37,796	36,396
Casualty Segment | Executive products
Segment Reporting
Net premiums earned	5,448	6,153	11,363	12,506
Casualty Segment | Other casualty
Segment Reporting
Net premiums earned	16,780	17,163	32,971	35,829
Property Segment
Segment Reporting
Net premiums earned	134,097	101,841	263,508	190,608
Property Segment | Commercial property
Segment Reporting
Net premiums earned	87,400	60,219	175,005	109,481
Property Segment | Marine
Segment Reporting
Net premiums earned	37,069	32,412	69,637	63,048
Property Segment | Other property
Segment Reporting
Net premiums earned	9,628	9,210	18,866	18,079
Surety Segment
Segment Reporting
Net premiums earned	35,868	33,391	68,857	66,316
Surety Segment | Transactional
Segment Reporting
Net premiums earned	12,308	11,887	24,416	23,934
Surety Segment | Commercial
Segment Reporting
Net premiums earned	12,700	12,505	23,325	24,923
Surety Segment | Contract
Segment Reporting
Net premiums earned	$ 10,860	$ 8,999	$ 21,116	$ 17,459

Leases - Schedule of Components

Leases - Schedule of Components of Lease Expense and Other lease Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Leases [Abstract]
Operating lease cost	$ 1,153	$ 1,239	$ 2,334	$ 2,508
Variable lease cost	260	444	508	882
Sublease income	(42)	(139)	(85)	(277)
Total lease cost	1,371	1,544	2,757	3,113
Cash paid for amounts included in measurement of lease liabilities
Operating cash outflows from operating leases	1,105	1,357	2,168	2,755
ROU assets obtained in exchange for new operating lease liabilities	333	$ 943	3,789	984
Reduction to ROU assets resulting from reduction to lease liabilities				$ 200
Operating lease ROU assets	$ 15,417		$ 15,417		$ 13,666
Operating Lease, Right-of-Use Asset, Statement of Financial Position	Other assets		Other assets		Other assets
Operating lease liabilities	$ 16,783		$ 16,783		$ 14,880
Operating Lease, Liability, Statement of Financial Position	Other liabilities		Other liabilities		Other liabilities
Weighted-average remaining lease term - operating leases	6 years 1 month 20 days		6 years 1 month 20 days		6 years 29 days
Weighted-average discount rate - operating leases	3.56%		3.56%		3.21%

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments under Non-cancellable Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Future minimum lease payments under non-cancellable leases
2024	$ 1,994
2025	4,197
2026	3,473
2027	2,107
2028	1,537
2029	1,443
Thereafter	4,489
Total future minimum lease payments	19,240
Less imputed interest	(2,457)
Operating lease liabilities	$ 16,783	$ 14,880

Acquisitions and Dispositions (

Acquisitions and Dispositions (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2023	Jun. 30, 2023
Dispositions
Cash proceeds from sale		$ 14,134
Maui Jim Inc. | Net Realized Gains
Dispositions
Recognized gain on sale	$ 14,000