RLI (RLI) 10-Q 26 Jul 23 2023 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2023	Jul. 17, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2023
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		45,596,196
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Statement [Abstract]
Net premiums earned	$ 322,280	$ 282,810	$ 630,003	$ 551,962
Net investment income	28,788	18,472	55,872	36,355
Net realized gains	5,580	12,804	20,200	18,392
Net unrealized gains (losses) on equity securities	25,214	(100,994)	40,710	(128,804)
Consolidated revenue	381,862	213,092	746,785	477,905
Losses and settlement expenses	153,943	117,914	268,431	223,438
Policy acquisition costs	102,626	89,615	204,070	174,902
Insurance operating expenses	24,510	19,325	48,411	38,188
Interest expense on debt	2,047	2,011	4,055	4,021
General corporate expenses	4,219	2,435	8,433	5,798
Total expenses	287,345	231,300	533,400	446,347
Equity in earnings of unconsolidated investees	1,514	11,654	5,437	20,413
Earnings (loss) before income taxes	96,031	(6,554)	218,822	51,971
Income tax expense (benefit)	18,379	(4,315)	42,359	6,287
Net earnings (loss)	77,652	(2,239)	176,463	45,684
Other comprehensive earnings (loss), net of tax	(19,721)	(97,563)	17,986	(213,144)
Comprehensive earnings (loss)	$ 57,931	$ (99,802)	$ 194,449	$ (167,460)
Basic net earnings (loss) per share	$ 1.70	$ (0.05)	$ 3.87	$ 1.01
Diluted net earnings (loss) per share	$ 1.69	$ (0.05)	$ 3.83	$ 1
Weighted average number of common shares outstanding:
Basic	45,591	45,354	45,560	45,330
Diluted	46,044	45,354	46,045	45,748

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
ASSETS
Available-for-sale, at fair value (amortized cost of $2,946,920 and allowance for credit losses of $434 at 6/30/23) (amortized cost of $2,945,273 and allowance for credit losses of $339 at 12/31/22)	$ 2,689,100	$ 2,666,950
Equity securities, at fair value (cost - $340,184 at 6/30/23 and $328,019 at 12/31/22)	552,566	498,382
Short-term investments, at cost which approximates fair value	271,296	36,229
Other invested assets	60,907	47,922
Cash	16,707	22,818
Total investments and cash	3,590,576	3,272,301
Accrued investment income	22,525	21,259
Premiums and reinsurance balances receivable, net of allowances for uncollectible amounts of $18,768 at 6/30/23 and $18,696 at 12/31/22	229,471	189,501
Ceded unearned premium	112,353	138,457
Reinsurance balances recoverable on unpaid losses and settlement expenses, net of allowances for uncollectible amounts of $10,251 at 6/30/23 and $11,250 at 12/31/22	720,858	740,089
Deferred policy acquisition costs	148,336	127,859
Property and equipment, at cost, net of accumulated depreciation of $72,404 at 6/30/23 and $68,633 at 12/31/22	48,358	49,573
Investment in unconsolidated investees	55,250	58,275
Goodwill and intangibles	53,562	53,562
Income taxes-deferred	29,864	40,269
Other assets	54,693	75,923
TOTAL ASSETS	5,065,846	4,767,068
Liabilities
Unpaid losses and settlement expenses	2,361,577	2,315,637
Unearned premiums	891,103	785,085
Reinsurance balances payable	35,931	61,100
Funds held	102,429	101,144
Income taxes-current	5,326
Current portion of long-term debt	199,956	199,863
Accrued expenses	70,220	94,869
Other liabilities	47,392	32,029
TOTAL LIABILITIES	3,713,934	3,589,727
Shareholders' Equity
Common stock ($0.01 par value) (Shares authorized - 200,000,000) (68,526,410 shares issued, 45,596,196 shares outstanding at 6/30/23) (68,399,966 shares issued, 45,469,752 shares outstanding at 12/31/22)	685	684
Paid-in capital	357,656	352,391
Accumulated other comprehensive earnings (loss)	(211,090)	(229,076)
Retained earnings	1,597,660	1,446,341
Deferred compensation	12,507	12,015
Treasury shares, at cost (22,930,214 shares at 6/30/23 and 12/31/22)	(405,506)	(405,014)
TOTAL SHAREHOLDERS' EQUITY	1,351,912	1,177,341
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 5,065,846	$ 4,767,068

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Statement Of Financial Position [Abstract]
Available-for-sale, amortized cost	$ 2,946,920	$ 2,945,273
Available-for-sale, allowance for credit losses	434	339
Equity securities, cost	340,184	328,019
Premiums and reinsurance balances receivable, allowances for uncollectible amounts	18,768	18,696
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	10,251	11,250
Property and equipment, accumulated depreciation	$ 72,404	$ 68,633
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)	68,526,410	68,399,966
Common stock, shares outstanding (in shares)	45,596,196	45,469,752
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
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2021	$ 682	$ 343,742	$ 49,826		$ 1,228,110	$ 9,642	$ (402,641)		$ 1,229,361
Shares, Outstanding, Beginning Balance at Dec. 31, 2021	45,289,337
Increase Decrease In Stockholders Equity Roll Forward
Net Income (Loss)					47,923				47,923
Other comprehensive earnings (loss), net of tax			(115,581)						(115,581)
Deferred compensation						(973)	973
Share-based compensation		3,049							3,049
Share-based compensation (in shares)	26,605
Dividends and dividend equivalents					(11,330)				(11,330)
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2022	$ 682	346,791	(65,755)		1,264,703	8,669	(401,668)		1,153,422
Shares, Outstanding, Ending Balance at Mar. 31, 2022	45,315,942
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2021	$ 682	343,742	49,826		1,228,110	9,642	(402,641)		1,229,361
Shares, Outstanding, Beginning Balance at Dec. 31, 2021	45,289,337
Increase Decrease In Stockholders Equity Roll Forward
Net Income (Loss)									45,684
Other comprehensive earnings (loss), net of tax									(213,144)
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2022	$ 683	349,161	(163,318)		1,250,661	8,945	(401,944)		1,044,188
Shares, Outstanding, Ending Balance at Jun. 30, 2022	45,368,804
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2022	$ 682	346,791	(65,755)		1,264,703	8,669	(401,668)		1,153,422
Shares, Outstanding, Beginning Balance at Mar. 31, 2022	45,315,942
Increase Decrease In Stockholders Equity Roll Forward
Net Income (Loss)					(2,239)				(2,239)
Other comprehensive earnings (loss), net of tax			(97,563)						(97,563)
Deferred compensation						276	(276)
Share-based compensation	$ 1	2,370							2,371
Share-based compensation (in shares)	52,862
Dividends and dividend equivalents					(11,803)				(11,803)
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2022	$ 683	349,161	(163,318)		1,250,661	8,945	(401,944)		1,044,188
Shares, Outstanding, Ending Balance at Jun. 30, 2022	45,368,804
Stockholders' 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 Stockholders 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)
Stockholders' 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
Stockholders' 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 Stockholders Equity Roll Forward
Net Income (Loss)									176,463
Other comprehensive earnings (loss), net of tax									17,986
Stockholders' 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
Stockholders' 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 Stockholders 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)
Stockholders' 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

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022
Statement Of Stockholders Equity [Abstract]
Cash dividends paid per common share	$ 0.27	$ 0.26	$ 0.26	$ 0.25

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Statement Of Cash Flows [Abstract]
Net cash provided by operating activities	$ 243,595	$ 170,645
Purchase of:
Fixed income securities, available-for-sale	(365,976)	(292,056)
Equity securities	(25,454)	(36,605)
Property and equipment	(2,790)	(3,024)
Other	(2,669)	(6,326)
Proceeds from sale of:
Fixed income securities - available-for-sale	19,490	20,892
Equity securities	22,029	53,525
Equity method investments	14,134
Other	473	1,172
Proceeds from call or maturity of:
Fixed income securities - available-for-sale	349,714	137,476
Net proceeds from sale (purchase) of short-term investments	(235,067)
Net cash used in investing activities	(226,116)	(124,946)
Cash Flows from Financing Activities
Cash dividends paid	(24,172)	(23,115)
Proceeds from stock option exercises	582	1,656
Net cash used in financing activities	(23,590)	(21,459)
Net increase in cash	(6,111)	24,240
Cash at the beginning of the period	22,818	88,804
Cash at June 30	$ 16,707	$ 113,044

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTES TO UNAUDITED CONDENSED CONSOLIDATED INTERIM FINANCIAL STATEMENTS ​ 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES ​ A. BASIS OF PRESENTATION ​ The unaudited condensed consolidated interim financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (GAAP) for interim financial reporting and with the instructions to Form 10-Q and Regulation S-X. Accordingly, they do not include all the disclosures required by GAAP for complete financial statements. As such, these unaudited condensed consolidated interim financial statements should be read in conjunction with our 2022 Annual Report on Form 10-K. Management believes that the disclosures are adequate to make the information presented not misleading, and all normal and recurring adjustments necessary to present fairly the financial position at June 30, 2023 and the results of operations of RLI Corp. (the Company) and subsidiaries for all periods presented have been made. The results of operations for any interim period are not necessarily indicative of the operating results for a full year. Certain reclassifications were made to 2022 to conform to the classifications used in the current year. ​ The preparation of the unaudited condensed consolidated interim 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 interim 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 ​ 2023-02—Investments – Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Method ​ The amendments in this ASU permit the use of the proportional amortization method for investments in tax credits if certain conditions are met. Under the proportional amortization method, the initial cost of an investment is amortized in proportion to the amount of tax credits and other tax benefits received, with the amortization and tax credits presented as a component of income tax expense. Under previous guidance, equity investments in tax credit structures, other than qualified affordable housing projects, were accounted for using the equity method of accounting, which required the presentation of income, gains and losses, and tax credits in their respective line items of the statement of earnings. This ASU allows entities to make an accounting policy election on an individual tax credit program basis for all equity investments whose primary purpose is receiving income tax credits or other income tax benefits. When the proportional amortization method is selected, this amendment also requires a liability be recognized for delayed equity contributions that are unconditional or for contingent contributions when the contingent event becomes probable. ​ We adopted ASU 2023-02 ​ C. PROSPECTIVE ACCOUNTING STANDARDS ​ There are no prospective accounting standards which would have a material impact on our financial statements as of June 30, 2023. ​ 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. In addition, we subject our reinsurance recoverables 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 each 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 recoverables for the reinsurer are specifically identified and written off through 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 recoverables were $16.2 million and $10.3 million, respectively, at June 30, 2023. At December 31, 2022, the amounts were $16.1 million and $11.3 million, respectively. 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 or recoveries were applied to the allowances in the first six months of 2023. We have no receivables with a due date that extends beyond one year that are not included in our allowance for uncollectible amounts. ​ E. INTANGIBLE ASSETS ​ The composition of goodwill and intangible assets at June 30, 2023 and December 31, 2022 is detailed in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (in thousands) 2023 2022 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 2023. Based upon these reviews, none of the assets were impaired. In addition, there were no triggering events as of June 30, 2023 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 interim financial statements: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Three Months ​ ​ Ended June 30, 2023 ​ Ended June 30, 2022 ​ ​ 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 ​ $ 77,652 ​ 45,591 ​ $ 1.70 ​ $ (2,239) ​ 45,354 ​ $ (0.05) Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 453 ​ ​ ​ ​ ​ — ​ — ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 77,652 ​ 46,044 ​ $ 1.69 ​ $ (2,239) ​ 45,354 ​ $ (0.05) Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ 736 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ For the Six Months ​ ​ Ended June 30, 2023 ​ Ended June 30, 2022 ​ ​ 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 ​ $ 176,463 ​ 45,560 ​ $ 3.87 ​ $ 45,684 ​ 45,330 ​ $ 1.01 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 485 ​ ​ ​ ​ ​ — ​ 418 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 176,463 ​ 46,045 ​ $ 3.83 ​ $ 45,684 ​ 45,748 ​ $ 1.00 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ 436 ​ ​ ​ ​ 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 $5 million for the second quarter of 2023, compared to $26 million of tax benefit for the same period in 2022. For the six-month period ended June 30, 2023, other comprehensive earnings (loss) is net of tax expense of $5 million, compared to $57 million of tax benefit for the same period in 2022. ​ Unrealized gains, net of tax, recognized in other comprehensive earnings (loss) were $18 million for the first six months of 2023, compared to $213 million of unrealized losses, net of tax, during the same period last year. The unrealized gains in 2023 were attributable to a decline in interest rates, which increased the fair value of securities held in the fixed income portfolio, compared to rising interest rates during 2022, which decreased the fair value of fixed income securities. ​ 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 interim 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 2023 2022 2023 2022 Beginning balance ​ $ (191,369) ​ $ (65,755) ​ $ (229,076) ​ $ 49,826 Other comprehensive earnings (loss) before reclassifications ​ ​ (20,347) ​ ​ (97,894) ​ ​ 15,908 ​ ​ (213,636) Amounts reclassified from accumulated other comprehensive earnings ​ ​ 626 ​ ​ 331 ​ ​ 2,078 ​ ​ 492 Net current-period other comprehensive earnings (loss) ​ $ (19,721) ​ $ (97,563) ​ $ 17,986 ​ $ (213,144) Ending balance ​ $ (211,090) ​ $ (163,318) ​ $ (211,090) ​ $ (163,318) Balance of securities for which an allowance for credit losses has been recognized in net earnings ​ ​ ​ ​ ​ ​ ​ $ 1,053 ​ $ 1,083 ​ 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) 2023 2022 2023 2022 ​ Statement of Earnings Unrealized gains and losses on available-for-sale securities ​ $ (824) ​ $ (722) ​ $ (2,536) ​ $ (772) ​ ​ Net realized gains (losses) ​ ​ ​ 31 ​ ​ 303 ​ ​ (95) ​ ​ 149 ​ ​ Credit gains presented within net realized gains ​ ​ $ (793) ​ $ (419) ​ $ (2,631) ​ $ (623) ​ ​ Earnings (loss) before income taxes ​ ​ ​ 167 ​ ​ 88 ​ ​ 553 ​ ​ 131 ​ ​ Income tax (expense) benefit ​ ​ $ (626) ​ $ (331) ​ $ (2,078) ​ $ (492) ​ ​ 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. ​ I. RISKS AND UNCERTAINTIES ​ Certain risks and uncertainties are inherent in our day-to-day operations. Adverse changes in the economy, including inflation; rising interest rates; volatile equity markets; and ongoing supply chain disruptions, could lower demand for our insurance products, result in increased levels of loss costs that we could not anticipate at the time we priced our coverages, or negatively impact our investment results, all of which could have an adverse effect on the profitability of our operations. ​ Catastrophe Exposures ​ Our catastrophe reinsurance treaty renewed on January 1, 2023. We purchased limits of $700 million in excess of $25 million first-dollar retention for earthquakes in California, $700 million in excess of $50 million first-dollar retention for earthquakes outside of California and $600 million in excess of $50 million first-dollar retention for all other perils, including wind. These amounts are subject to certain co-participations by the Company on losses in excess of the first-dollar retentions. On June 1, 2023, we purchased $150 million of additional catastrophe reinsurance protection on top of the previously described coverage. This increases the limits to $850 million in excess of $25 million first-dollar retention for earthquakes in California, $850 million in excess of $50 million first-dollar retention for earthquakes outside of California and $750 million in excess of $50 million first-dollar retention for all other perils, including wind, all of which are still subject to certain co-participations in excess of the retentions.

Investments

Investments	6 Months Ended
	Jun. 30, 2023
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 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, 2023 and 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Sales ​ Proceeds ​ Gross Realized ​ Net Realized (in thousands) From Sales Gains Losses Gain (Loss) 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 20,729 ​ $ 99 ​ $ (910) ​ $ (811) Equity securities ​ ​ 22,029 ​ ​ 8,841 ​ ​ (101) ​ ​ 8,740 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 19,390 ​ $ 215 ​ $ (432) ​ $ (217) Equity securities ​ ​ 53,525 ​ ​ 19,244 ​ ​ (15) ​ ​ 19,229 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Calls/Maturities ​ ​ ​ ​ Gross Realized ​ Net Realized (in thousands) Proceeds Gains Losses Gain (Loss) 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 349,734 ​ $ 37 ​ $ (43) ​ $ (6) 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 137,499 ​ $ 76 ​ $ (55) ​ $ 21 ​ FAIR VALUE MEASUREMENTS ​ Assets measured at fair value on a recurring basis as of June 30, 2023 and December 31, 2022 are summarized below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of June 30, 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 ​ $ — ​ $ 315,976 ​ $ — ​ $ 315,976 U.S. agency ​ ​ — ​ ​ 43,719 ​ ​ — ​ ​ 43,719 Non-U.S. government & agency ​ ​ — ​ ​ 3,960 ​ ​ — ​ ​ 3,960 Agency MBS ​ ​ — ​ ​ 372,030 ​ ​ — ​ ​ 372,030 ABS/CMBS/MBS* ​ ​ — ​ ​ 252,330 ​ ​ — ​ ​ 252,330 Corporate ​ ​ — ​ ​ 1,095,038 ​ ​ 52,466 ​ ​ 1,147,504 Municipal ​ ​ — ​ ​ 553,581 ​ ​ — ​ ​ 553,581 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,636,634 ​ $ 52,466 ​ $ 2,689,100 Equity securities ​ ​ 550,986 ​ ​ — ​ ​ 1,580 ​ ​ 552,566 Total ​ $ 550,986 ​ $ 2,636,634 ​ $ 54,046 ​ $ 3,241,666 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2022 ​ ​ 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 ​ $ — ​ $ 454,021 ​ $ — ​ $ 454,021 U.S. agency ​ ​ — ​ ​ 73,063 ​ ​ — ​ ​ 73,063 Non-U.S. government & agency ​ ​ — ​ ​ 5,847 ​ ​ — ​ ​ 5,847 Agency MBS ​ ​ — ​ ​ 331,806 ​ ​ — ​ ​ 331,806 ABS/CMBS/MBS* ​ ​ — ​ ​ 240,736 ​ ​ — ​ ​ 240,736 Corporate ​ ​ — ​ ​ 980,676 ​ ​ 53,654 ​ ​ 1,034,330 Municipal ​ ​ — ​ ​ 527,147 ​ ​ — ​ ​ 527,147 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,613,296 ​ $ 53,654 ​ $ 2,666,950 Equity securities ​ ​ 496,731 ​ ​ 39 ​ ​ 1,612 ​ ​ 498,382 Total ​ $ 496,731 ​ $ 2,613,335 ​ $ 55,266 ​ $ 3,165,332 * 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, 2023 ​ $ 55,266 Net realized and unrealized gains (losses) ​ ​ ​ Included in other comprehensive earnings (loss) ​ ​ 551 Sales / Calls / Maturities ​ ​ (1,771) Balance as of June 30, 2023 ​ $ 54,046 Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - included in other comprehensive earnings (loss) ​ $ 551 ​ The amortized cost and fair value of available-for-sale fixed income securities by contractual maturity as of June 30, 2023 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2023 (in thousands) Amortized Cost Fair Value Due in one year or less ​ $ 195,245 ​ $ 193,554 Due after one year through five years ​ ​ 910,005 ​ ​ 861,351 Due after five years through 10 years ​ ​ 567,327 ​ ​ 529,864 Due after 10 years ​ ​ 573,985 ​ ​ 479,971 ABS/CMBS/MBS* ​ ​ 700,358 ​ ​ 624,360 Total available-for-sale ​ $ 2,946,920 ​ $ 2,689,100 * Asset-backed, commercial mortgage-backed and mortgage-backed securities ​ The amortized cost and fair value of available-for-sale securities at June 30, 2023 and December 31, 2022 are presented in the tables below. Amortized cost does not include the $22 million and $20 million of accrued interest receivable as of June 30, 2023 and December 31, 2022, respectively. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2023 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 325,893 ​ $ — ​ $ — ​ $ (9,917) ​ $ 315,976 U.S. agency ​ ​ 45,937 ​ ​ — ​ ​ — ​ ​ (2,218) ​ ​ 43,719 Non-U.S. government & agency ​ ​ 4,799 ​ ​ — ​ ​ — ​ ​ (839) ​ ​ 3,960 Agency MBS ​ ​ 414,503 ​ ​ — ​ ​ 206 ​ ​ (42,679) ​ ​ 372,030 ABS/CMBS/MBS* ​ ​ 285,855 ​ ​ (5) ​ ​ 78 ​ ​ (33,598) ​ ​ 252,330 Corporate ​ ​ 1,227,628 ​ ​ (429) ​ ​ 1,872 ​ ​ (81,567) ​ ​ 1,147,504 Municipal ​ ​ 642,305 ​ ​ — ​ ​ 1,397 ​ ​ (90,121) ​ ​ 553,581 Total Fixed Income ​ $ 2,946,920 ​ $ (434) ​ $ 3,553 ​ $ (260,939) ​ $ 2,689,100 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 462,884 ​ $ — ​ $ 8 ​ $ (8,871) ​ $ 454,021 U.S. agency ​ ​ 75,074 ​ ​ — ​ ​ 26 ​ ​ (2,037) ​ ​ 73,063 Non-U.S. government & agency ​ ​ 6,798 ​ ​ — ​ ​ — ​ ​ (951) ​ ​ 5,847 Agency MBS ​ ​ 373,687 ​ ​ — ​ ​ 336 ​ ​ (42,217) ​ ​ 331,806 ABS/CMBS/MBS* ​ ​ 276,126 ​ ​ (8) ​ ​ 62 ​ ​ (35,444) ​ ​ 240,736 Corporate ​ ​ 1,122,097 ​ ​ (331) ​ ​ 541 ​ ​ (87,977) ​ ​ 1,034,330 Municipal ​ ​ 628,607 ​ ​ — ​ ​ 1,265 ​ ​ (102,725) ​ ​ 527,147 Total Fixed Income ​ $ 2,945,273 ​ $ (339) ​ $ 2,238 ​ $ (280,222) ​ $ 2,666,950 * 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, 2023, the discounted cash flow analysis resulted in an allowance for credit losses on 18 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) 2023 2022 2023 2022 Beginning balance ​ $ 465 ​ $ 594 ​ $ 339 ​ $ 441 Increase to allowance from securities for which credit losses were not previously recorded ​ ​ 2 ​ ​ 149 ​ ​ 25 ​ ​ 223 Reduction from securities sold during the period ​ ​ — ​ ​ (433) ​ ​ — ​ ​ (433) Reductions from intent to sell securities ​ ​ — ​ ​ — ​ ​ — ​ ​ (17) Net increase (decrease) from securities that had an allowance at the beginning of the period ​ ​ (33) ​ ​ (18) ​ ​ 70 ​ ​ 78 Balance as of June 30, ​ $ 434 ​ $ 292 ​ $ 434 ​ $ 292 ​ During the first six months of 2023, net realized gains included $1.7 million of losses on fixed income securities for which the cost basis was written down to fair value due to a credit event and restructurings. We recognized $0.1 million of losses on securities for which we no longer had the intent to hold until recovery during the first six months of 2022. ​ As of June 30, 2023, in addition to the securities included in the allowance for credit losses, the fixed income portfolio contained 1,474 securities with an unrealized loss position for which an allowance for credit losses had not been recorded. The $261 million in associated unrealized losses represents 9 percent of the fixed income portfolio’s cost basis and 7 percent of total invested assets. Isolated to these securities, unrealized losses decreased through the first six months of 2023, as credit spreads have tightened modestly while interest rates stayed flat during the period. Of the total 1,474 securities, 995 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, 2023 and December 31, 2022 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, 2023 ​ December 31, 2022 (in thousands) < 12 Mos. 12 Mos. & Greater Total < 12 Mos. 12 Mos. & Greater Total U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 220,227 ​ $ 95,748 ​ $ 315,975 ​ $ 399,361 ​ $ 8,828 ​ $ 408,189 Amortized cost ​ ​ 225,987 ​ ​ 99,905 ​ ​ 325,892 ​ ​ 407,340 ​ ​ 9,720 ​ ​ 417,060 Unrealized loss ​ $ (5,760) ​ $ (4,157) ​ $ (9,917) ​ $ (7,979) ​ $ (892) ​ $ (8,871) U.S. agency ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 33,951 ​ $ 9,768 ​ $ 43,719 ​ $ 32,987 ​ $ 2,170 ​ $ 35,157 Amortized cost ​ ​ 34,975 ​ ​ 10,962 ​ ​ 45,937 ​ ​ 34,627 ​ ​ 2,567 ​ ​ 37,194 Unrealized loss ​ $ (1,024) ​ $ (1,194) ​ $ (2,218) ​ $ (1,640) ​ $ (397) ​ $ (2,037) Non-U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 658 ​ $ 3,302 ​ $ 3,960 ​ $ 3,626 ​ $ 2,221 ​ $ 5,847 Amortized cost ​ ​ 702 ​ ​ 4,097 ​ ​ 4,799 ​ ​ 3,798 ​ ​ 3,000 ​ ​ 6,798 Unrealized Loss ​ $ (44) ​ $ (795) ​ $ (839) ​ $ (172) ​ $ (779) ​ $ (951) Agency MBS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 141,545 ​ $ 216,878 ​ $ 358,423 ​ $ 197,252 ​ $ 117,851 ​ $ 315,103 Amortized cost ​ ​ 146,150 ​ ​ 254,952 ​ ​ 401,102 ​ ​ 212,776 ​ ​ 144,544 ​ ​ 357,320 Unrealized loss ​ $ (4,605) ​ $ (38,074) ​ $ (42,679) ​ $ (15,524) ​ $ (26,693) ​ $ (42,217) ABS/CMBS/MBS* ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 20,483 ​ $ 219,639 ​ $ 240,122 ​ $ 96,754 ​ $ 136,149 ​ $ 232,903 Amortized cost ​ ​ 21,028 ​ ​ 252,692 ​ ​ 273,720 ​ ​ 104,724 ​ ​ 163,623 ​ ​ 268,347 Unrealized loss ​ $ (545) ​ $ (33,053) ​ $ (33,598) ​ $ (7,970) ​ $ (27,474) ​ $ (35,444) Corporate ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 429,215 ​ $ 607,324 ​ $ 1,036,539 ​ $ 660,830 ​ $ 323,337 ​ $ 984,167 Amortized cost ​ ​ 441,843 ​ ​ 676,263 ​ ​ 1,118,106 ​ ​ 697,437 ​ ​ 374,707 ​ ​ 1,072,144 Unrealized loss ​ $ (12,628) ​ $ (68,939) ​ $ (81,567) ​ $ (36,607) ​ $ (51,370) ​ $ (87,977) Municipal ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 131,486 ​ $ 362,776 ​ $ 494,262 ​ $ 228,827 ​ $ 204,324 ​ $ 433,151 Amortized cost ​ ​ 133,340 ​ ​ 451,043 ​ ​ 584,383 ​ ​ 255,240 ​ ​ 280,636 ​ ​ 535,876 Unrealized loss ​ $ (1,854) ​ $ (88,267) ​ $ (90,121) ​ $ (26,413) ​ $ (76,312) ​ $ (102,725) Total fixed income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 977,565 ​ $ 1,515,435 ​ $ 2,493,000 ​ $ 1,619,637 ​ $ 794,880 ​ $ 2,414,517 Amortized cost ​ ​ 1,004,025 ​ ​ 1,749,914 ​ ​ 2,753,939 ​ ​ 1,715,942 ​ ​ 978,797 ​ ​ 2,694,739 Unrealized loss ​ $ (26,460) ​ $ (234,479) ​ $ (260,939) ​ $ (96,305) ​ $ (183,917) ​ $ (280,222) * 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, 2023 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 ​ $ 2,269,819 ​ $ 2,052,151 ​ $ (217,668) ​ 83.4 % 2 ​ BBB ​ Baa ​ ​ 404,162 ​ ​ 366,729 ​ ​ (37,433) ​ 14.4 % 3 ​ BB ​ Ba ​ ​ 45,298 ​ ​ 41,464 ​ ​ (3,834) ​ 1.5 % 4 ​ B ​ B ​ ​ 32,264 ​ ​ 30,844 ​ ​ (1,420) ​ 0.5 % 5 ​ CCC ​ Caa ​ ​ 2,396 ​ ​ 1,812 ​ ​ (584) ​ 0.2 % 6 ​ CC or lower ​ Ca or lower ​ ​ — ​ ​ — ​ ​ — ​ 0.0 % ​ ​ ​ ​ Total ​ $ 2,753,939 ​ $ 2,493,000 ​ $ (260,939) ​ 100.0 % ​ Other Invested Assets ​ We had $61 million of other invested assets at June 30, 2023, compared to $48 million at December 31, 2022. 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 $12 million at June 30, 2023, compared to $13 million on December 31, 2022. Our LIHTC interests recognized amortization of $0.8 million as a component of income tax expense and a total tax benefit of $0.8 million during the second quarter of 2023, compared to $0.8 million of amortization and $0.9 million of tax benefit during the same period in 2022. For the six-months ended June 30, 2023, our LIHTC interest recognized amortization of $1.6 million and a total benefit of $1.6 million, compared to $1.7 million of amortization and $1.7 million of tax benefit for the same period in 2022. Our unfunded commitment for our LIHTC investments totaled $1 million at June 30, 2023 and will be paid out in installments through 2035. ​ Our HTC investment had a balance of $15 million at June 30, 2023, compared to $11 million at December 31, 2022. Through 2022, the investment was accounted for as an investment in unconsolidated investee. Due to the adoption of ASU 2023-02, Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method ​ As of June 30, 2023, $56 million of investments were pledged as collateral with the FHLBC to ensure timely access to the secured lending facility that ownership of FHLBC stock provides. As of June 30, 2023, $50 million of borrowings were outstanding with the FHLBC. ​ Our investments in private funds totaled $27 million as of June 30, 2023, down from $28 million as of December 31, 2022, and had $5 million of associated unfunded commitments at June 30, 2023. 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 $55 million of investments in unconsolidated investees at June 30, 2023, compared to $58 million at December 31, 2022. At June 30, 2023, our investment in Prime Holdings Insurance Services, Inc. (Prime) was $55 million and other investments in unconsolidated investees totaled less than $1 million. Through December 31, 2022, our $11 million HTC investment was accounted for as an unconsolidated investee, but was reclassified as an other invested asset during 2023 due to the adoption of ASU 2023-02. ​ 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 $17 million and $271 million, respectively, at June 30, 2023, compared to $23 million and $36 million, respectively, at December 31, 2022.

Historical Loss And LAE Develop

Historical Loss And LAE Development	6 Months Ended
	Jun. 30, 2023
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 2023 and 2022: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ ​ Ended June 30, (in thousands) 2023 2022 Unpaid losses and LAE at beginning of year ​ ​ ​ ​ ​ ​ Gross ​ $ 2,315,637 ​ $ 2,043,555 Ceded ​ ​ (740,089) ​ ​ (608,086) Net ​ $ 1,575,548 ​ $ 1,435,469 ​ ​ ​ ​ ​ ​ ​ Increase (decrease) in incurred losses and LAE ​ ​ ​ ​ ​ ​ Current accident year ​ $ 339,951 ​ $ 293,158 Prior accident years ​ ​ (71,520) ​ ​ (69,720) Total incurred ​ $ 268,431 ​ $ 223,438 ​ ​ ​ ​ ​ ​ ​ Loss and LAE payments for claims incurred ​ ​ ​ ​ ​ ​ Current accident year ​ $ (30,978) ​ $ (21,628) Prior accident years ​ ​ (172,282) ​ ​ (153,490) Total paid ​ $ (203,260) ​ $ (175,118) ​ ​ ​ ​ ​ ​ ​ Net unpaid losses and LAE at June 30, ​ $ 1,640,719 ​ $ 1,483,789 ​ ​ ​ ​ ​ ​ ​ Unpaid losses and LAE at June 30, ​ ​ ​ ​ ​ ​ Gross ​ $ 2,361,577 ​ $ 2,150,519 Ceded ​ ​ (720,858) ​ ​ (666,730) Net ​ $ 1,640,719 ​ $ 1,483,789 ​ 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. ​ For the first six months of 2022, incurred losses and LAE included $70 million of favorable development on prior years’ loss reserves, largely from accident years 2018 through 2021. General liability, professional services, transportation, marine and surety were drivers of the favorable development. No products experienced significant adverse development.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	4. INCOME TAXES ​ Our effective tax rate for the three and six months ended June 30, 2023 was 19.1 percent and 19.4 percent, respectively, compared to 65.8 percent and 12.1 percent, respectively, for the same period in 2022. Effective rates are dependent upon components of pretax earnings and the related tax effects. Tax-favored adjustments acting on pretax earnings resulted in a lower effective tax rate for the second quarter of 2023. The effective tax rate was higher for the six-month period in 2023, as higher pretax income decreased the percentage impact of tax-favored adjustments. ​ Income tax expense attributable to income from operations for the three and six-month period ended June 30, 2023 and 2022 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 below table. 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, 2023 ​ For the Six Months Ended June 30, 2023 ​ ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 ​ (in thousands) Amount % Amount % Amount % Amount % ​ Provision for income taxes at the statutory rate of 21% ​ $ 20,167 ​ 21.0 % $ (1,376) ​ 21.0 % $ 45,953 ​ 21.0 % $ 10,914 ​ 21.0 % Increase (reduction) in taxes resulting from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Excess tax benefit on share-based compensation ​ ​ (878) ​ (0.9) % ​ (761) ​ 11.6 % ​ (2,868) ​ (1.3) % ​ (2,175) ​ (4.2) % Tax exempt interest income ​ ​ (274) ​ (0.3) % ​ (288) ​ 4.4 % ​ (557) ​ (0.3) % ​ (570) ​ (1.1) % Dividends received deduction ​ ​ (209) ​ (0.2) % ​ (163) ​ 2.5 % ​ (433) ​ (0.2) % ​ (434) ​ (0.8) % Tax credit ​ ​ (780) ​ (0.8) % ​ (1,461) ​ 22.3 % ​ (1,559) ​ (0.7) % ​ (2,922) ​ (5.6) % ESOP dividends paid deduction ​ ​ (144) ​ (0.2) % ​ (138) ​ 2.1 % ​ (281) ​ (0.1) % ​ (268) ​ (0.5) % Nondeductible expenses ​ ​ 745 ​ 0.8 % ​ 258 ​ (3.9) % ​ 1,346 ​ 0.6 % ​ 574 ​ 1.1 % Other items, net ​ ​ (248) ​ (0.3) % ​ (386) ​ 5.8 % ​ 758 ​ 0.4 % ​ 1,168 ​ 2.2 % Total tax expense ​ $ 18,379 ​ 19.1 % $ (4,315) ​ 65.8 % $ 42,359 ​ 19.4 % $ 6,287 ​ 12.1 % ​ 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 will generate sufficient taxable income to realize the deferred tax asset.

Stock Based Compensation

Stock Based Compensation	6 Months Ended
	Jun. 30, 2023
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 135,838 awards under the 2023 LTIP. ​ 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 $4.7 million in the three and six-month periods ended June 30, 2023, respectively, compared to $2.3 million and $3.7 million, respectively, for the same period in 2022. The total income tax benefit was $0.3 million and $0.8 million for the three and six-month periods ended June 30, 2023, compared to $0.4 million and $0.6 million, respectively, for the same periods in 2022. Total unrecognized compensation expense relating to outstanding and unvested awards was $8 million, which will be recognized over the weighted average vesting period of 2.77 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, 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ Aggregate ​ ​ ​ ​ Weighted ​ Average ​ Intrinsic ​ ​ ​ ​ Average ​ Remaining ​ Value ​ Options Exercise Price Contractual Life (in 000’s) Outstanding options at January 1, 2023 ​ 1,695,660 ​ $ 82.42 ​ ​ ​ ​ ​ Options granted ​ 144,375 ​ ​ 135.72 ​ ​ ​ ​ ​ Options exercised ​ (199,145) ​ ​ 56.17 ​ ​ ​ ​ ​ Options canceled/forfeited ​ (1,000) ​ ​ 40.61 ​ ​ ​ ​ ​ Outstanding options at June 30, 2023 ​ 1,639,890 ​ $ 90.33 ​ 5.01 ​ $ 75,687 Exercisable options at June 30, 2023 ​ 806,436 ​ $ 75.52 ​ 3.78 ​ $ 49,154 ​ The intrinsic value, which is the difference between the fair value and the exercise price, of options exercised was $16 million and $5 million during the first six months of 2023 and 2022, 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: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2023 2022 ​ Weighted-average fair value of grants ​ $ 26.79 ​ $ 21.05 ​ Risk-free interest rates ​ ​ 3.44 % ​ 2.84 % Dividend yield ​ ​ 2.29 % ​ 2.50 % Expected volatility ​ ​ 22.95 % ​ 22.89 % Expected option life ​ ​ 4.94 years ​ 5.06 years ​ The risk-free rate was determined based on U.S. treasury yields that most closely approximated the option’s 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 $1 million and $2 million during the first six months of 2023 and 2022, respectively. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ RSUs Fair Value Nonvested at January 1, 2023 ​ 44,208 ​ $ 109.51 Granted ​ 19,063 ​ ​ 136.33 Reinvested ​ 206 ​ ​ 129.72 Vested ​ (6,748) ​ ​ 118.66 Forfeited ​ (732) ​ ​ 136.58 Nonvested at June 30, 2023 ​ 55,997 ​ $ 117.49 ​

Operating Segment Information

Operating Segment Information	6 Months Ended
	Jun. 30, 2023
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) 2023 2022 2023 2022 Casualty ​ $ 187,048 ​ $ 177,123 ​ $ 373,079 ​ $ 348,879 Property ​ ​ 101,841 ​ ​ 74,690 ​ ​ 190,608 ​ ​ 142,130 Surety ​ ​ 33,391 ​ ​ 30,997 ​ ​ 66,316 ​ ​ 60,953 Net premiums earned ​ $ 322,280 ​ $ 282,810 ​ $ 630,003 ​ $ 551,962 Net investment income ​ ​ 28,788 ​ ​ 18,472 ​ ​ 55,872 ​ ​ 36,355 Net realized gains ​ ​ 5,580 ​ ​ 12,804 ​ ​ 20,200 ​ ​ 18,392 Net unrealized gains (losses) on equity securities ​ ​ 25,214 ​ ​ (100,994) ​ ​ 40,710 ​ ​ (128,804) Total consolidated revenue ​ $ 381,862 ​ $ 213,092 ​ $ 746,785 ​ $ 477,905 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Earnings ​ ​ ​ ​ ​ ​ (in thousands) 2023 2022 2023 2022 Casualty ​ $ 6,977 ​ $ 21,442 ​ $ 38,808 ​ $ 49,089 Property ​ ​ 25,877 ​ ​ 26,105 ​ ​ 54,260 ​ ​ 48,581 Surety ​ ​ 8,347 ​ ​ 8,409 ​ ​ 16,023 ​ ​ 17,764 Net underwriting income ​ $ 41,201 ​ $ 55,956 ​ $ 109,091 ​ $ 115,434 Net investment income ​ ​ 28,788 ​ ​ 18,472 ​ ​ 55,872 ​ ​ 36,355 Net realized gains ​ ​ 5,580 ​ ​ 12,804 ​ ​ 20,200 ​ ​ 18,392 Net unrealized gains (losses) on equity securities ​ ​ 25,214 ​ ​ (100,994) ​ ​ 40,710 ​ ​ (128,804) General corporate expense and interest on debt ​ ​ (6,266) ​ ​ (4,446) ​ ​ (12,488) ​ ​ (9,819) Equity in earnings of unconsolidated investees ​ ​ 1,514 ​ ​ 11,654 ​ ​ 5,437 ​ ​ 20,413 Earnings (loss) before income taxes ​ $ 96,031 ​ $ (6,554) ​ $ 218,822 ​ $ 51,971 Income tax expense (benefit) ​ ​ 18,379 ​ ​ (4,315) ​ ​ 42,359 ​ ​ 6,287 Net earnings (loss) ​ $ 77,652 ​ $ (2,239) ​ $ 176,463 ​ $ 45,684 ​ 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) 2023 2022 2023 2022 Casualty ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial excess and personal umbrella ​ $ 69,261 ​ $ 62,463 ​ $ 136,843 ​ $ 122,535 General liability ​ ​ 26,016 ​ ​ 25,106 ​ ​ 51,916 ​ ​ 48,846 Commercial transportation ​ ​ 25,398 ​ ​ 23,941 ​ ​ 50,630 ​ ​ 47,569 Professional services ​ ​ 24,602 ​ ​ 23,861 ​ ​ 48,959 ​ ​ 47,416 Small commercial ​ ​ 18,455 ​ ​ 16,813 ​ ​ 36,396 ​ ​ 33,458 Executive products ​ ​ 6,153 ​ ​ 7,075 ​ ​ 12,506 ​ ​ 13,652 Other casualty ​ ​ 17,163 ​ ​ 17,864 ​ ​ 35,829 ​ ​ 35,403 Total ​ $ 187,048 ​ $ 177,123 ​ $ 373,079 ​ $ 348,879 Property ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial property ​ $ 60,219 ​ $ 38,929 ​ $ 109,481 ​ $ 72,218 Marine ​ ​ 32,412 ​ ​ 28,178 ​ ​ 63,048 ​ ​ 54,907 Other property ​ ​ 9,210 ​ ​ 7,583 ​ ​ 18,079 ​ ​ 15,005 Total ​ $ 101,841 ​ $ 74,690 ​ $ 190,608 ​ $ 142,130 Surety ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial ​ $ 12,505 ​ $ 11,663 ​ $ 24,923 ​ $ 23,366 Miscellaneous ​ ​ 11,887 ​ ​ 11,587 ​ ​ 23,934 ​ ​ 22,940 Contract ​ ​ 8,999 ​ ​ 7,747 ​ ​ 17,459 ​ ​ 14,647 Total ​ $ 33,391 ​ $ 30,997 ​ $ 66,316 ​ $ 60,953 Grand Total ​ $ 322,280 ​ $ 282,810 ​ $ 630,003 ​ $ 551,962 ​

Leases

Leases	6 Months Ended
	Jun. 30, 2023
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 cost for future minimum lease payments is recognized on a straight-line basis over the lease term. Variable lease cost is expensed in the period in which the obligation is 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, 2023 and 2022 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Six Months ​ ​ Ended June 30, ​ Ended June 30, (in thousands) 2023 2022 2023 2022 Operating lease cost ​ $ 1,239 ​ $ 1,256 ​ $ 2,508 ​ $ 2,414 Variable lease cost ​ ​ 444 ​ ​ 349 ​ ​ 882 ​ ​ 695 Sublease income ​ ​ (139) ​ ​ (139) ​ ​ (277) ​ ​ (277) Total lease cost ​ $ 1,544 ​ $ 1,466 ​ $ 3,113 ​ $ 2,832 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash paid for amounts included in measurement of lease liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating cash outflows from operating leases ​ $ 1,357 ​ $ 1,278 ​ $ 2,755 ​ $ 2,600 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ 943 ​ $ 2,431 ​ $ 984 ​ $ 2,431 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reduction to ROU assets resulting from reduction to lease liabilities ​ $ — ​ $ — ​ $ 200 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other non-cash reductions to ROU assets ​ $ — ​ $ — ​ $ — ​ $ 73 ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) June 30, 2023 December 31, 2022 ​ Operating lease ROU assets ​ $ 11,185 ​ $ 12,766 ​ Operating lease liabilities ​ $ 12,635 ​ $ 14,499 ​ Weighted-average remaining lease term - operating leases ​ ​ 4.18 years ​ 4.21 years Weighted-average discount rate - operating leases ​ ​ 1.97 % ​ 2.11 % ​ Future minimum lease payments under non-cancellable leases as of June 30, 2023 were as follows: ​ ​ ​ ​ ​ (in thousands) June 30, 2023 2023 ​ $ 2,636 2024 ​ ​ 3,827 2025 ​ ​ 2,551 2026 ​ ​ 1,646 2027 ​ ​ 997 2028 ​ ​ 704 Thereafter ​ ​ 883 Total future minimum lease payments ​ $ 13,244 Less imputed interest ​ ​ (609) Total operating lease liability ​ $ 12,635 ​

Acquisitions and Dispositions

Acquisitions and Dispositions	6 Months Ended
	Jun. 30, 2023
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 for cash proceeds of $687 million. A net realized gain of $571 million was recognized during 2022 and the payout of the working capital escrow during the first quarter of 2023 resulted in the recognition of an additional $14 million realized gain. The gains were recorded in the net realized gain line item of the statement of earnings.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	A. BASIS OF PRESENTATION ​ The unaudited condensed consolidated interim financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (GAAP) for interim financial reporting and with the instructions to Form 10-Q and Regulation S-X. Accordingly, they do not include all the disclosures required by GAAP for complete financial statements. As such, these unaudited condensed consolidated interim financial statements should be read in conjunction with our 2022 Annual Report on Form 10-K. Management believes that the disclosures are adequate to make the information presented not misleading, and all normal and recurring adjustments necessary to present fairly the financial position at June 30, 2023 and the results of operations of RLI Corp. (the Company) and subsidiaries for all periods presented have been made. The results of operations for any interim period are not necessarily indicative of the operating results for a full year. Certain reclassifications were made to 2022 to conform to the classifications used in the current year. ​ The preparation of the unaudited condensed consolidated interim 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 interim 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 ​ 2023-02—Investments – Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Method ​ The amendments in this ASU permit the use of the proportional amortization method for investments in tax credits if certain conditions are met. Under the proportional amortization method, the initial cost of an investment is amortized in proportion to the amount of tax credits and other tax benefits received, with the amortization and tax credits presented as a component of income tax expense. Under previous guidance, equity investments in tax credit structures, other than qualified affordable housing projects, were accounted for using the equity method of accounting, which required the presentation of income, gains and losses, and tax credits in their respective line items of the statement of earnings. This ASU allows entities to make an accounting policy election on an individual tax credit program basis for all equity investments whose primary purpose is receiving income tax credits or other income tax benefits. When the proportional amortization method is selected, this amendment also requires a liability be recognized for delayed equity contributions that are unconditional or for contingent contributions when the contingent event becomes probable. ​ We adopted ASU 2023-02
Prospective Accounting Standards	​ C. PROSPECTIVE ACCOUNTING STANDARDS ​ There are no prospective accounting standards which would have a material impact on our financial statements as of June 30, 2023.
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. In addition, we subject our reinsurance recoverables 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 each 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 recoverables for the reinsurer are specifically identified and written off through 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 recoverables were $16.2 million and $10.3 million, respectively, at June 30, 2023. At December 31, 2022, the amounts were $16.1 million and $11.3 million, respectively. 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 or recoveries were applied to the allowances in the first six months of 2023. We have no receivables with a due date that extends beyond one year that are not included in our allowance for uncollectible amounts. ​
Goodwill and Intangible Assets	E. INTANGIBLE ASSETS ​ The composition of goodwill and intangible assets at June 30, 2023 and December 31, 2022 is detailed in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (in thousands) 2023 2022 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 2023. Based upon these reviews, none of the assets were impaired. In addition, there were no triggering events as of June 30, 2023 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 interim financial statements: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months ​ For the Three Months ​ ​ Ended June 30, 2023 ​ Ended June 30, 2022 ​ ​ 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 ​ $ 77,652 ​ 45,591 ​ $ 1.70 ​ $ (2,239) ​ 45,354 ​ $ (0.05) Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 453 ​ ​ ​ ​ ​ — ​ — ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 77,652 ​ 46,044 ​ $ 1.69 ​ $ (2,239) ​ 45,354 ​ $ (0.05) Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ 736 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ For the Six Months ​ ​ Ended June 30, 2023 ​ Ended June 30, 2022 ​ ​ 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 ​ $ 176,463 ​ 45,560 ​ $ 3.87 ​ $ 45,684 ​ 45,330 ​ $ 1.01 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 485 ​ ​ ​ ​ ​ — ​ 418 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 176,463 ​ 46,045 ​ $ 3.83 ​ $ 45,684 ​ 45,748 ​ $ 1.00 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ 436 ​ ​ ​ ​
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 $5 million for the second quarter of 2023, compared to $26 million of tax benefit for the same period in 2022. For the six-month period ended June 30, 2023, other comprehensive earnings (loss) is net of tax expense of $5 million, compared to $57 million of tax benefit for the same period in 2022. ​ Unrealized gains, net of tax, recognized in other comprehensive earnings (loss) were $18 million for the first six months of 2023, compared to $213 million of unrealized losses, net of tax, during the same period last year. The unrealized gains in 2023 were attributable to a decline in interest rates, which increased the fair value of securities held in the fixed income portfolio, compared to rising interest rates during 2022, which decreased the fair value of fixed income securities. ​ 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 interim 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 2023 2022 2023 2022 Beginning balance ​ $ (191,369) ​ $ (65,755) ​ $ (229,076) ​ $ 49,826 Other comprehensive earnings (loss) before reclassifications ​ ​ (20,347) ​ ​ (97,894) ​ ​ 15,908 ​ ​ (213,636) Amounts reclassified from accumulated other comprehensive earnings ​ ​ 626 ​ ​ 331 ​ ​ 2,078 ​ ​ 492 Net current-period other comprehensive earnings (loss) ​ $ (19,721) ​ $ (97,563) ​ $ 17,986 ​ $ (213,144) Ending balance ​ $ (211,090) ​ $ (163,318) ​ $ (211,090) ​ $ (163,318) Balance of securities for which an allowance for credit losses has been recognized in net earnings ​ ​ ​ ​ ​ ​ ​ $ 1,053 ​ $ 1,083 ​ 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) 2023 2022 2023 2022 ​ Statement of Earnings Unrealized gains and losses on available-for-sale securities ​ $ (824) ​ $ (722) ​ $ (2,536) ​ $ (772) ​ ​ Net realized gains (losses) ​ ​ ​ 31 ​ ​ 303 ​ ​ (95) ​ ​ 149 ​ ​ Credit gains presented within net realized gains ​ ​ $ (793) ​ $ (419) ​ $ (2,631) ​ $ (623) ​ ​ Earnings (loss) before income taxes ​ ​ ​ 167 ​ ​ 88 ​ ​ 553 ​ ​ 131 ​ ​ Income tax (expense) benefit ​ ​ $ (626) ​ $ (331) ​ $ (2,078) ​ $ (492) ​ ​ Net earnings (loss)
Fair Value Disclosures	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.
Risks and Uncertainties	I. RISKS AND UNCERTAINTIES ​ Certain risks and uncertainties are inherent in our day-to-day operations. Adverse changes in the economy, including inflation; rising interest rates; volatile equity markets; and ongoing supply chain disruptions, could lower demand for our insurance products, result in increased levels of loss costs that we could not anticipate at the time we priced our coverages, or negatively impact our investment results, all of which could have an adverse effect on the profitability of our operations. ​ Catastrophe Exposures ​ Our catastrophe reinsurance treaty renewed on January 1, 2023. We purchased limits of $700 million in excess of $25 million first-dollar retention for earthquakes in California, $700 million in excess of $50 million first-dollar retention for earthquakes outside of California and $600 million in excess of $50 million first-dollar retention for all other perils, including wind. These amounts are subject to certain co-participations by the Company on losses in excess of the first-dollar retentions. On June 1, 2023, we purchased $150 million of additional catastrophe reinsurance protection on top of the previously described coverage. This increases the limits to $850 million in excess of $25 million first-dollar retention for earthquakes in California, $850 million in excess of $50 million first-dollar retention for earthquakes outside of California and $750 million in excess of $50 million first-dollar retention for all other perils, including wind, all of which are still subject to certain co-participations in excess of the retentions.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Schedule of Goodwill and Intangible Assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (in thousands) 2023 2022 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, 2023 ​ Ended June 30, 2022 ​ ​ 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 ​ $ 77,652 ​ 45,591 ​ $ 1.70 ​ $ (2,239) ​ 45,354 ​ $ (0.05) Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 453 ​ ​ ​ ​ ​ — ​ — ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 77,652 ​ 46,044 ​ $ 1.69 ​ $ (2,239) ​ 45,354 ​ $ (0.05) Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ 736 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Six Months ​ For the Six Months ​ ​ Ended June 30, 2023 ​ Ended June 30, 2022 ​ ​ 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 ​ $ 176,463 ​ 45,560 ​ $ 3.87 ​ $ 45,684 ​ 45,330 ​ $ 1.01 Effect of Dilutive Securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock options and restricted stock units ​ ​ — ​ 485 ​ ​ ​ ​ ​ — ​ 418 ​ ​ ​ Diluted EPS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings available to common shareholders ​ $ 176,463 ​ 46,045 ​ $ 3.83 ​ $ 45,684 ​ 45,748 ​ $ 1.00 Anti-dilutive securities excluded from diluted EPS ​ ​ ​ ​ ​ 118 ​ ​ ​ ​ ​ ​ ​ ​ 436 ​ ​ ​ ​
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 2023 2022 2023 2022 Beginning balance ​ $ (191,369) ​ $ (65,755) ​ $ (229,076) ​ $ 49,826 Other comprehensive earnings (loss) before reclassifications ​ ​ (20,347) ​ ​ (97,894) ​ ​ 15,908 ​ ​ (213,636) Amounts reclassified from accumulated other comprehensive earnings ​ ​ 626 ​ ​ 331 ​ ​ 2,078 ​ ​ 492 Net current-period other comprehensive earnings (loss) ​ $ (19,721) ​ $ (97,563) ​ $ 17,986 ​ $ (213,144) Ending balance ​ $ (211,090) ​ $ (163,318) ​ $ (211,090) ​ $ (163,318) Balance of securities for which an allowance for credit losses has been recognized in net earnings ​ ​ ​ ​ ​ ​ ​ $ 1,053 ​ $ 1,083
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) 2023 2022 2023 2022 ​ Statement of Earnings Unrealized gains and losses on available-for-sale securities ​ $ (824) ​ $ (722) ​ $ (2,536) ​ $ (772) ​ ​ Net realized gains (losses) ​ ​ ​ 31 ​ ​ 303 ​ ​ (95) ​ ​ 149 ​ ​ Credit gains presented within net realized gains ​ ​ $ (793) ​ $ (419) ​ $ (2,631) ​ $ (623) ​ ​ Earnings (loss) before income taxes ​ ​ ​ 167 ​ ​ 88 ​ ​ 553 ​ ​ 131 ​ ​ Income tax (expense) benefit ​ ​ $ (626) ​ $ (331) ​ $ (2,078) ​ $ (492) ​ ​ Net earnings (loss)

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2023
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) 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 20,729 ​ $ 99 ​ $ (910) ​ $ (811) Equity securities ​ ​ 22,029 ​ ​ 8,841 ​ ​ (101) ​ ​ 8,740 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 19,390 ​ $ 215 ​ $ (432) ​ $ (217) Equity securities ​ ​ 53,525 ​ ​ 19,244 ​ ​ (15) ​ ​ 19,229 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Calls/Maturities ​ ​ ​ ​ Gross Realized ​ Net Realized (in thousands) Proceeds Gains Losses Gain (Loss) 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 349,734 ​ $ 37 ​ $ (43) ​ $ (6) 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fixed income securities - available-for-sale ​ $ 137,499 ​ $ 76 ​ $ (55) ​ $ 21
Fair Value, Assets Measured on Recurring Basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of June 30, 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 ​ $ — ​ $ 315,976 ​ $ — ​ $ 315,976 U.S. agency ​ ​ — ​ ​ 43,719 ​ ​ — ​ ​ 43,719 Non-U.S. government & agency ​ ​ — ​ ​ 3,960 ​ ​ — ​ ​ 3,960 Agency MBS ​ ​ — ​ ​ 372,030 ​ ​ — ​ ​ 372,030 ABS/CMBS/MBS* ​ ​ — ​ ​ 252,330 ​ ​ — ​ ​ 252,330 Corporate ​ ​ — ​ ​ 1,095,038 ​ ​ 52,466 ​ ​ 1,147,504 Municipal ​ ​ — ​ ​ 553,581 ​ ​ — ​ ​ 553,581 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,636,634 ​ $ 52,466 ​ $ 2,689,100 Equity securities ​ ​ 550,986 ​ ​ — ​ ​ 1,580 ​ ​ 552,566 Total ​ $ 550,986 ​ $ 2,636,634 ​ $ 54,046 ​ $ 3,241,666 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2022 ​ ​ 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 ​ $ — ​ $ 454,021 ​ $ — ​ $ 454,021 U.S. agency ​ ​ — ​ ​ 73,063 ​ ​ — ​ ​ 73,063 Non-U.S. government & agency ​ ​ — ​ ​ 5,847 ​ ​ — ​ ​ 5,847 Agency MBS ​ ​ — ​ ​ 331,806 ​ ​ — ​ ​ 331,806 ABS/CMBS/MBS* ​ ​ — ​ ​ 240,736 ​ ​ — ​ ​ 240,736 Corporate ​ ​ — ​ ​ 980,676 ​ ​ 53,654 ​ ​ 1,034,330 Municipal ​ ​ — ​ ​ 527,147 ​ ​ — ​ ​ 527,147 Total fixed income securities - available-for-sale ​ $ — ​ $ 2,613,296 ​ $ 53,654 ​ $ 2,666,950 Equity securities ​ ​ 496,731 ​ ​ 39 ​ ​ 1,612 ​ ​ 498,382 Total ​ $ 496,731 ​ $ 2,613,335 ​ $ 55,266 ​ $ 3,165,332 * 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, 2023 ​ $ 55,266 Net realized and unrealized gains (losses) ​ ​ ​ Included in other comprehensive earnings (loss) ​ ​ 551 Sales / Calls / Maturities ​ ​ (1,771) Balance as of June 30, 2023 ​ $ 54,046 Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - included in other comprehensive earnings (loss) ​ $ 551
Schedule of Contractual Maturity of Securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2023 (in thousands) Amortized Cost Fair Value Due in one year or less ​ $ 195,245 ​ $ 193,554 Due after one year through five years ​ ​ 910,005 ​ ​ 861,351 Due after five years through 10 years ​ ​ 567,327 ​ ​ 529,864 Due after 10 years ​ ​ 573,985 ​ ​ 479,971 ABS/CMBS/MBS* ​ ​ 700,358 ​ ​ 624,360 Total available-for-sale ​ $ 2,946,920 ​ $ 2,689,100 * Asset-backed, commercial mortgage-backed and mortgage-backed securities
Schedule of Amortized Cost and Fair Value of Available-for-sale Securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2023 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 325,893 ​ $ — ​ $ — ​ $ (9,917) ​ $ 315,976 U.S. agency ​ ​ 45,937 ​ ​ — ​ ​ — ​ ​ (2,218) ​ ​ 43,719 Non-U.S. government & agency ​ ​ 4,799 ​ ​ — ​ ​ — ​ ​ (839) ​ ​ 3,960 Agency MBS ​ ​ 414,503 ​ ​ — ​ ​ 206 ​ ​ (42,679) ​ ​ 372,030 ABS/CMBS/MBS* ​ ​ 285,855 ​ ​ (5) ​ ​ 78 ​ ​ (33,598) ​ ​ 252,330 Corporate ​ ​ 1,227,628 ​ ​ (429) ​ ​ 1,872 ​ ​ (81,567) ​ ​ 1,147,504 Municipal ​ ​ 642,305 ​ ​ — ​ ​ 1,397 ​ ​ (90,121) ​ ​ 553,581 Total Fixed Income ​ $ 2,946,920 ​ $ (434) ​ $ 3,553 ​ $ (260,939) ​ $ 2,689,100 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 ​ ​ Cost or ​ Allowance ​ Gross ​ Gross ​ ​ ​ ​ ​ Amortized ​ for Credit ​ Unrealized ​ Unrealized ​ Fair (in thousands) Cost Losses Gains Losses Value U.S. government ​ $ 462,884 ​ $ — ​ $ 8 ​ $ (8,871) ​ $ 454,021 U.S. agency ​ ​ 75,074 ​ ​ — ​ ​ 26 ​ ​ (2,037) ​ ​ 73,063 Non-U.S. government & agency ​ ​ 6,798 ​ ​ — ​ ​ — ​ ​ (951) ​ ​ 5,847 Agency MBS ​ ​ 373,687 ​ ​ — ​ ​ 336 ​ ​ (42,217) ​ ​ 331,806 ABS/CMBS/MBS* ​ ​ 276,126 ​ ​ (8) ​ ​ 62 ​ ​ (35,444) ​ ​ 240,736 Corporate ​ ​ 1,122,097 ​ ​ (331) ​ ​ 541 ​ ​ (87,977) ​ ​ 1,034,330 Municipal ​ ​ 628,607 ​ ​ — ​ ​ 1,265 ​ ​ (102,725) ​ ​ 527,147 Total Fixed Income ​ $ 2,945,273 ​ $ (339) ​ $ 2,238 ​ $ (280,222) ​ $ 2,666,950 * 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) 2023 2022 2023 2022 Beginning balance ​ $ 465 ​ $ 594 ​ $ 339 ​ $ 441 Increase to allowance from securities for which credit losses were not previously recorded ​ ​ 2 ​ ​ 149 ​ ​ 25 ​ ​ 223 Reduction from securities sold during the period ​ ​ — ​ ​ (433) ​ ​ — ​ ​ (433) Reductions from intent to sell securities ​ ​ — ​ ​ — ​ ​ — ​ ​ (17) Net increase (decrease) from securities that had an allowance at the beginning of the period ​ ​ (33) ​ ​ (18) ​ ​ 70 ​ ​ 78 Balance as of June 30, ​ $ 434 ​ $ 292 ​ $ 434 ​ $ 292
Schedule of Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2023 ​ December 31, 2022 (in thousands) < 12 Mos. 12 Mos. & Greater Total < 12 Mos. 12 Mos. & Greater Total U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 220,227 ​ $ 95,748 ​ $ 315,975 ​ $ 399,361 ​ $ 8,828 ​ $ 408,189 Amortized cost ​ ​ 225,987 ​ ​ 99,905 ​ ​ 325,892 ​ ​ 407,340 ​ ​ 9,720 ​ ​ 417,060 Unrealized loss ​ $ (5,760) ​ $ (4,157) ​ $ (9,917) ​ $ (7,979) ​ $ (892) ​ $ (8,871) U.S. agency ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 33,951 ​ $ 9,768 ​ $ 43,719 ​ $ 32,987 ​ $ 2,170 ​ $ 35,157 Amortized cost ​ ​ 34,975 ​ ​ 10,962 ​ ​ 45,937 ​ ​ 34,627 ​ ​ 2,567 ​ ​ 37,194 Unrealized loss ​ $ (1,024) ​ $ (1,194) ​ $ (2,218) ​ $ (1,640) ​ $ (397) ​ $ (2,037) Non-U.S. government ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 658 ​ $ 3,302 ​ $ 3,960 ​ $ 3,626 ​ $ 2,221 ​ $ 5,847 Amortized cost ​ ​ 702 ​ ​ 4,097 ​ ​ 4,799 ​ ​ 3,798 ​ ​ 3,000 ​ ​ 6,798 Unrealized Loss ​ $ (44) ​ $ (795) ​ $ (839) ​ $ (172) ​ $ (779) ​ $ (951) Agency MBS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 141,545 ​ $ 216,878 ​ $ 358,423 ​ $ 197,252 ​ $ 117,851 ​ $ 315,103 Amortized cost ​ ​ 146,150 ​ ​ 254,952 ​ ​ 401,102 ​ ​ 212,776 ​ ​ 144,544 ​ ​ 357,320 Unrealized loss ​ $ (4,605) ​ $ (38,074) ​ $ (42,679) ​ $ (15,524) ​ $ (26,693) ​ $ (42,217) ABS/CMBS/MBS* ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 20,483 ​ $ 219,639 ​ $ 240,122 ​ $ 96,754 ​ $ 136,149 ​ $ 232,903 Amortized cost ​ ​ 21,028 ​ ​ 252,692 ​ ​ 273,720 ​ ​ 104,724 ​ ​ 163,623 ​ ​ 268,347 Unrealized loss ​ $ (545) ​ $ (33,053) ​ $ (33,598) ​ $ (7,970) ​ $ (27,474) ​ $ (35,444) Corporate ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 429,215 ​ $ 607,324 ​ $ 1,036,539 ​ $ 660,830 ​ $ 323,337 ​ $ 984,167 Amortized cost ​ ​ 441,843 ​ ​ 676,263 ​ ​ 1,118,106 ​ ​ 697,437 ​ ​ 374,707 ​ ​ 1,072,144 Unrealized loss ​ $ (12,628) ​ $ (68,939) ​ $ (81,567) ​ $ (36,607) ​ $ (51,370) ​ $ (87,977) Municipal ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 131,486 ​ $ 362,776 ​ $ 494,262 ​ $ 228,827 ​ $ 204,324 ​ $ 433,151 Amortized cost ​ ​ 133,340 ​ ​ 451,043 ​ ​ 584,383 ​ ​ 255,240 ​ ​ 280,636 ​ ​ 535,876 Unrealized loss ​ $ (1,854) ​ $ (88,267) ​ $ (90,121) ​ $ (26,413) ​ $ (76,312) ​ $ (102,725) Total fixed income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value ​ $ 977,565 ​ $ 1,515,435 ​ $ 2,493,000 ​ $ 1,619,637 ​ $ 794,880 ​ $ 2,414,517 Amortized cost ​ ​ 1,004,025 ​ ​ 1,749,914 ​ ​ 2,753,939 ​ ​ 1,715,942 ​ ​ 978,797 ​ ​ 2,694,739 Unrealized loss ​ $ (26,460) ​ $ (234,479) ​ $ (260,939) ​ $ (96,305) ​ $ (183,917) ​ $ (280,222) * 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 ​ $ 2,269,819 ​ $ 2,052,151 ​ $ (217,668) ​ 83.4 % 2 ​ BBB ​ Baa ​ ​ 404,162 ​ ​ 366,729 ​ ​ (37,433) ​ 14.4 % 3 ​ BB ​ Ba ​ ​ 45,298 ​ ​ 41,464 ​ ​ (3,834) ​ 1.5 % 4 ​ B ​ B ​ ​ 32,264 ​ ​ 30,844 ​ ​ (1,420) ​ 0.5 % 5 ​ CCC ​ Caa ​ ​ 2,396 ​ ​ 1,812 ​ ​ (584) ​ 0.2 % 6 ​ CC or lower ​ Ca or lower ​ ​ — ​ ​ — ​ ​ — ​ 0.0 % ​ ​ ​ ​ Total ​ $ 2,753,939 ​ $ 2,493,000 ​ $ (260,939) ​ 100.0 %

Historical Loss And LAE Devel_2

Historical Loss And LAE Development (Tables)	6 Months Ended
	Jun. 30, 2023
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) 2023 2022 Unpaid losses and LAE at beginning of year ​ ​ ​ ​ ​ ​ Gross ​ $ 2,315,637 ​ $ 2,043,555 Ceded ​ ​ (740,089) ​ ​ (608,086) Net ​ $ 1,575,548 ​ $ 1,435,469 ​ ​ ​ ​ ​ ​ ​ Increase (decrease) in incurred losses and LAE ​ ​ ​ ​ ​ ​ Current accident year ​ $ 339,951 ​ $ 293,158 Prior accident years ​ ​ (71,520) ​ ​ (69,720) Total incurred ​ $ 268,431 ​ $ 223,438 ​ ​ ​ ​ ​ ​ ​ Loss and LAE payments for claims incurred ​ ​ ​ ​ ​ ​ Current accident year ​ $ (30,978) ​ $ (21,628) Prior accident years ​ ​ (172,282) ​ ​ (153,490) Total paid ​ $ (203,260) ​ $ (175,118) ​ ​ ​ ​ ​ ​ ​ Net unpaid losses and LAE at June 30, ​ $ 1,640,719 ​ $ 1,483,789 ​ ​ ​ ​ ​ ​ ​ Unpaid losses and LAE at June 30, ​ ​ ​ ​ ​ ​ Gross ​ $ 2,361,577 ​ $ 2,150,519 Ceded ​ ​ (720,858) ​ ​ (666,730) Net ​ $ 1,640,719 ​ $ 1,483,789

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2023
Income Tax Disclosure [Abstract]
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, 2023 ​ For the Six Months Ended June 30, 2023 ​ ​ ​ 2023 ​ 2022 ​ 2023 ​ 2022 ​ (in thousands) Amount % Amount % Amount % Amount % ​ Provision for income taxes at the statutory rate of 21% ​ $ 20,167 ​ 21.0 % $ (1,376) ​ 21.0 % $ 45,953 ​ 21.0 % $ 10,914 ​ 21.0 % Increase (reduction) in taxes resulting from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Excess tax benefit on share-based compensation ​ ​ (878) ​ (0.9) % ​ (761) ​ 11.6 % ​ (2,868) ​ (1.3) % ​ (2,175) ​ (4.2) % Tax exempt interest income ​ ​ (274) ​ (0.3) % ​ (288) ​ 4.4 % ​ (557) ​ (0.3) % ​ (570) ​ (1.1) % Dividends received deduction ​ ​ (209) ​ (0.2) % ​ (163) ​ 2.5 % ​ (433) ​ (0.2) % ​ (434) ​ (0.8) % Tax credit ​ ​ (780) ​ (0.8) % ​ (1,461) ​ 22.3 % ​ (1,559) ​ (0.7) % ​ (2,922) ​ (5.6) % ESOP dividends paid deduction ​ ​ (144) ​ (0.2) % ​ (138) ​ 2.1 % ​ (281) ​ (0.1) % ​ (268) ​ (0.5) % Nondeductible expenses ​ ​ 745 ​ 0.8 % ​ 258 ​ (3.9) % ​ 1,346 ​ 0.6 % ​ 574 ​ 1.1 % Other items, net ​ ​ (248) ​ (0.3) % ​ (386) ​ 5.8 % ​ 758 ​ 0.4 % ​ 1,168 ​ 2.2 % Total tax expense ​ $ 18,379 ​ 19.1 % $ (4,315) ​ 65.8 % $ 42,359 ​ 19.4 % $ 6,287 ​ 12.1 %

Stock Based Compensation (Table

Stock Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2023
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, 2023 ​ 1,695,660 ​ $ 82.42 ​ ​ ​ ​ ​ Options granted ​ 144,375 ​ ​ 135.72 ​ ​ ​ ​ ​ Options exercised ​ (199,145) ​ ​ 56.17 ​ ​ ​ ​ ​ Options canceled/forfeited ​ (1,000) ​ ​ 40.61 ​ ​ ​ ​ ​ Outstanding options at June 30, 2023 ​ 1,639,890 ​ $ 90.33 ​ 5.01 ​ $ 75,687 Exercisable options at June 30, 2023 ​ 806,436 ​ $ 75.52 ​ 3.78 ​ $ 49,154
Summary of Weighted Average Grant-date Assumptions and Weighted Average Fair Values	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2023 2022 ​ Weighted-average fair value of grants ​ $ 26.79 ​ $ 21.05 ​ Risk-free interest rates ​ ​ 3.44 % ​ 2.84 % Dividend yield ​ ​ 2.29 % ​ 2.50 % Expected volatility ​ ​ 22.95 % ​ 22.89 % Expected option life ​ ​ 4.94 years ​ 5.06 years
Schedule of Restricted Stock Units Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ RSUs Fair Value Nonvested at January 1, 2023 ​ 44,208 ​ $ 109.51 Granted ​ 19,063 ​ ​ 136.33 Reinvested ​ 206 ​ ​ 129.72 Vested ​ (6,748) ​ ​ 118.66 Forfeited ​ (732) ​ ​ 136.58 Nonvested at June 30, 2023 ​ 55,997 ​ $ 117.49

Operating Segment Information (

Operating Segment Information (Tables)	6 Months Ended
	Jun. 30, 2023
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) 2023 2022 2023 2022 Casualty ​ $ 187,048 ​ $ 177,123 ​ $ 373,079 ​ $ 348,879 Property ​ ​ 101,841 ​ ​ 74,690 ​ ​ 190,608 ​ ​ 142,130 Surety ​ ​ 33,391 ​ ​ 30,997 ​ ​ 66,316 ​ ​ 60,953 Net premiums earned ​ $ 322,280 ​ $ 282,810 ​ $ 630,003 ​ $ 551,962 Net investment income ​ ​ 28,788 ​ ​ 18,472 ​ ​ 55,872 ​ ​ 36,355 Net realized gains ​ ​ 5,580 ​ ​ 12,804 ​ ​ 20,200 ​ ​ 18,392 Net unrealized gains (losses) on equity securities ​ ​ 25,214 ​ ​ (100,994) ​ ​ 40,710 ​ ​ (128,804) Total consolidated revenue ​ $ 381,862 ​ $ 213,092 ​ $ 746,785 ​ $ 477,905 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Earnings ​ ​ ​ ​ ​ ​ (in thousands) 2023 2022 2023 2022 Casualty ​ $ 6,977 ​ $ 21,442 ​ $ 38,808 ​ $ 49,089 Property ​ ​ 25,877 ​ ​ 26,105 ​ ​ 54,260 ​ ​ 48,581 Surety ​ ​ 8,347 ​ ​ 8,409 ​ ​ 16,023 ​ ​ 17,764 Net underwriting income ​ $ 41,201 ​ $ 55,956 ​ $ 109,091 ​ $ 115,434 Net investment income ​ ​ 28,788 ​ ​ 18,472 ​ ​ 55,872 ​ ​ 36,355 Net realized gains ​ ​ 5,580 ​ ​ 12,804 ​ ​ 20,200 ​ ​ 18,392 Net unrealized gains (losses) on equity securities ​ ​ 25,214 ​ ​ (100,994) ​ ​ 40,710 ​ ​ (128,804) General corporate expense and interest on debt ​ ​ (6,266) ​ ​ (4,446) ​ ​ (12,488) ​ ​ (9,819) Equity in earnings of unconsolidated investees ​ ​ 1,514 ​ ​ 11,654 ​ ​ 5,437 ​ ​ 20,413 Earnings (loss) before income taxes ​ $ 96,031 ​ $ (6,554) ​ $ 218,822 ​ $ 51,971 Income tax expense (benefit) ​ ​ 18,379 ​ ​ (4,315) ​ ​ 42,359 ​ ​ 6,287 Net earnings (loss) ​ $ 77,652 ​ $ (2,239) ​ $ 176,463 ​ $ 45,684
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) 2023 2022 2023 2022 Casualty ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial excess and personal umbrella ​ $ 69,261 ​ $ 62,463 ​ $ 136,843 ​ $ 122,535 General liability ​ ​ 26,016 ​ ​ 25,106 ​ ​ 51,916 ​ ​ 48,846 Commercial transportation ​ ​ 25,398 ​ ​ 23,941 ​ ​ 50,630 ​ ​ 47,569 Professional services ​ ​ 24,602 ​ ​ 23,861 ​ ​ 48,959 ​ ​ 47,416 Small commercial ​ ​ 18,455 ​ ​ 16,813 ​ ​ 36,396 ​ ​ 33,458 Executive products ​ ​ 6,153 ​ ​ 7,075 ​ ​ 12,506 ​ ​ 13,652 Other casualty ​ ​ 17,163 ​ ​ 17,864 ​ ​ 35,829 ​ ​ 35,403 Total ​ $ 187,048 ​ $ 177,123 ​ $ 373,079 ​ $ 348,879 Property ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial property ​ $ 60,219 ​ $ 38,929 ​ $ 109,481 ​ $ 72,218 Marine ​ ​ 32,412 ​ ​ 28,178 ​ ​ 63,048 ​ ​ 54,907 Other property ​ ​ 9,210 ​ ​ 7,583 ​ ​ 18,079 ​ ​ 15,005 Total ​ $ 101,841 ​ $ 74,690 ​ $ 190,608 ​ $ 142,130 Surety ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Commercial ​ $ 12,505 ​ $ 11,663 ​ $ 24,923 ​ $ 23,366 Miscellaneous ​ ​ 11,887 ​ ​ 11,587 ​ ​ 23,934 ​ ​ 22,940 Contract ​ ​ 8,999 ​ ​ 7,747 ​ ​ 17,459 ​ ​ 14,647 Total ​ $ 33,391 ​ $ 30,997 ​ $ 66,316 ​ $ 60,953 Grand Total ​ $ 322,280 ​ $ 282,810 ​ $ 630,003 ​ $ 551,962

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2023
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) 2023 2022 2023 2022 Operating lease cost ​ $ 1,239 ​ $ 1,256 ​ $ 2,508 ​ $ 2,414 Variable lease cost ​ ​ 444 ​ ​ 349 ​ ​ 882 ​ ​ 695 Sublease income ​ ​ (139) ​ ​ (139) ​ ​ (277) ​ ​ (277) Total lease cost ​ $ 1,544 ​ $ 1,466 ​ $ 3,113 ​ $ 2,832 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash paid for amounts included in measurement of lease liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating cash outflows from operating leases ​ $ 1,357 ​ $ 1,278 ​ $ 2,755 ​ $ 2,600 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ 943 ​ $ 2,431 ​ $ 984 ​ $ 2,431 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reduction to ROU assets resulting from reduction to lease liabilities ​ $ — ​ $ — ​ $ 200 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other non-cash reductions to ROU assets ​ $ — ​ $ — ​ $ — ​ $ 73 ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) June 30, 2023 December 31, 2022 ​ Operating lease ROU assets ​ $ 11,185 ​ $ 12,766 ​ Operating lease liabilities ​ $ 12,635 ​ $ 14,499 ​ Weighted-average remaining lease term - operating leases ​ ​ 4.18 years ​ 4.21 years Weighted-average discount rate - operating leases ​ ​ 1.97 % ​ 2.11 % ​
Schedule of Future Minimum Lease Payments under Non-cancellable Leases	​ ​ ​ ​ ​ (in thousands) June 30, 2023 2023 ​ $ 2,636 2024 ​ ​ 3,827 2025 ​ ​ 2,551 2026 ​ ​ 1,646 2027 ​ ​ 997 2028 ​ ​ 704 Thereafter ​ ​ 883 Total future minimum lease payments ​ $ 13,244 Less imputed interest ​ ​ (609) Total operating lease liability ​ $ 12,635

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Adopted Accounting Standards (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Jun. 30, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated investees	$ 58,275	$ 55,250
Other Investments	47,922	60,907
Retained earnings	$ 1,446,341	1,597,660
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible Enumeration]	rli:AccountingStandardsUpdate202302Member
Historic tax credit partnerships (HTC)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated investees	$ 11,000
Other Investments		15,000
Equity investments in tax credit structures, unfunded commitment		$ 4,000
Historic tax credit partnerships (HTC) | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity investments in tax credit structures, unfunded commitment	7,000
Retained earnings	(1,000)
Historic tax credit partnerships (HTC) | Cumulative Effect, Period of Adoption, Adjustment | Other Invested Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Investments	$ 11,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reinsurance - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Amount of allowance for uncollectible amounts on paid recoverables	$ 16,200,000	$ 16,100,000
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	10,251,000	$ 11,250,000
Financing receivable, allowance for credit Loss, write-off	0
Amount of allowance for uncollectible amounts due beyond one year	$ 0
Threshold period for including reinsurance receivables in the allowance for uncollectible amounts	1 year

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Goodwill and Intangible Assets - Schedule of Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Business Acquisition
Goodwill	$ 46,062	$ 46,062
Indefinite-lived intangibles	7,500	7,500
Total goodwill and intangibles	53,562	53,562
Surety
Business Acquisition
Goodwill	40,816	40,816
Casualty
Business Acquisition
Goodwill	$ 5,246	$ 5,246

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Goodwill and Intangible Assets - Additional Information (Details)	3 Months Ended
	Jun. 30, 2023 USD ($)
Accounting Policies [Abstract]
Goodwill and intangible asset impairment	$ 0

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Schedule of Reconciliation of Numerator and Denominator of the Basic and Diluted Earnings Per Share Computations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Basic EPS, Income (Numerator)
Earnings available to common shareholders	$ 77,652	$ (2,239)	$ 176,463	$ 45,684
Diluted EPS, Income (Numerator)
Earnings available to common shareholders	$ 77,652	$ (2,239)	$ 176,463	$ 45,684
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	45,591	45,354	45,560	45,330
Effect of Dilutive Securities, Shares (Denominator)
Stock options and restricted stock units	453		485	418
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	46,044	45,354	46,045	45,748
Earnings Per Share, Diluted, Other Disclosures
Anti-dilutive securities excluded from diluted EPS	118	736	118	436
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)	$ 1.70	$ (0.05)	$ 3.87	$ 1.01
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.69	$ (0.05)	$ 3.83	$ 1

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Comprehensive Earnings (Loss) - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
COMPREHENSIVE EARNINGS (LOSS)
Tax rate used (as a percent)	21%		21%		21%	21%
Other comprehensive earnings (loss), tax (benefit)	$ (5,000)		$ (26,000)		$ 5,000	$ (57,000)
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Other comprehensive earnings (loss), net of tax	$ (19,721)	$ 37,707	$ (97,563)	$ (115,581)	$ 17,986	$ (213,144)

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Schedule of Changes in the Balance of Each Component of Accumulated Other Comprehensive Earnings (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Beginning balance		$ (229,076)			$ (229,076)
Net current-period other comprehensive earnings (loss)	$ (19,721)	37,707	$ (97,563)	$ (115,581)	17,986	$ (213,144)
Ending balance	(211,090)				(211,090)
Unrealized Gains and Losses on Available-for-Sale Securities
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Beginning balance	(191,369)	(229,076)	(65,755)	49,826	(229,076)	49,826
Other comprehensive earnings (loss) before reclassifications	(20,347)		(97,894)		15,908	(213,636)
Amounts reclassified from accumulated other comprehensive earnings	626		331		2,078	492
Net current-period other comprehensive earnings (loss)	(19,721)		(97,563)		17,986	(213,144)
Ending balance	(211,090)	$ (191,369)	(163,318)	$ (65,755)	(211,090)	(163,318)
Balance of securities for which an allowance for credit losses has not been recognized in net earnings	$ 1,053		$ 1,083		$ 1,053	$ 1,083

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Schedule of Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss)
Earnings (loss) before income taxes	$ 96,031		$ (6,554)		$ 218,822	$ 51,971
Income tax (expense) benefit	(18,379)		4,315		(42,359)	(6,287)
Net earnings (loss)	77,652	$ 98,811	(2,239)	$ 47,923	176,463	45,684
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	(824)		(722)		(2,536)	(772)
Credit gains presented within net realized gains	31		303		(95)	149
Earnings (loss) before income taxes	(793)		(419)		(2,631)	(623)
Income tax (expense) benefit	167		88		553	131
Net earnings (loss)	$ (626)		$ (331)		$ (2,078)	$ (492)

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Catastrophe Exposures - Additional Information (Details) - USD ($) $ in Millions	Jun. 01, 2023	Jan. 01, 2023
California Earthquake
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	$ 850	$ 700
First-dollar retention	25	25
Outside of California Earthquake
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	850	700
First-dollar retention	50	50
Other Perils including Wind
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	750	600
First-dollar retention	50	$ 50
Catastrophe
Liability For Catastrophe Claims [Line Items]
Additional catastrophe reinsurance	$ 150

Investments - Disposition of Fi

Investments - Disposition of Fixed Income and Equity Securities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Summary of the disposition of fixed income and equity securities
Fixed income securities - available-for-sale	$ 19,490	$ 20,892
Fixed income securities - available-for-sale	349,714	137,476
SALES
Summary of the disposition of fixed income and equity securities
Fixed income securities - available-for-sale	20,729	19,390
Gross Realized Gains - Fixed income securities - available-for-sale	99	215
Gross Realized Losses - Fixed income securities - available-for-sale	(910)	(432)
Net Realized Gain (Loss) - Fixed income securities - available-for-sale	(811)	(217)
Proceeds from Sales - Equity securities	22,029	53,525
Gross Realized Gains - Equity securities	8,841	19,244
Gross Realized Losses - Equity securities	(101)	(15)
Net Realized Gain (Loss) - Equity securities	8,740	19,229
Calls And Maturities Of Marketable Securities
Summary of the disposition of fixed income and equity securities
Fixed income securities - available-for-sale	349,734	137,499
Gross Realized Gains - Fixed income securities - available-for-sale	37	76
Gross Realized Losses - Fixed income securities - available-for-sale	(43)	(55)
Net Realized Gain (Loss) - Fixed income securities - available-for-sale	$ (6)	$ 21

Investments - Assets Measured a

Investments - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Assets measured at Fair Value
Available-for-sale fixed income	$ 2,689,100	$ 2,666,950
Equity securities	552,566	498,382
U.S. government
Assets measured at Fair Value
Available-for-sale fixed income	315,976	454,021
U.S. Agency
Assets measured at Fair Value
Available-for-sale fixed income	43,719	73,063
Non-U.S. government & agency
Assets measured at Fair Value
Available-for-sale fixed income	3,960	5,847
Agency MBS
Assets measured at Fair Value
Available-for-sale fixed income	372,030	331,806
ABS/CMBS/MBS
Assets measured at Fair Value
Available-for-sale fixed income	252,330	240,736
Corporate Debt
Assets measured at Fair Value
Available-for-sale fixed income	1,147,504	1,034,330
Municipal
Assets measured at Fair Value
Available-for-sale fixed income	553,581	527,147
Fair Value Measured on Recurring Basis
Assets measured at Fair Value
Available-for-sale fixed income	2,689,100	2,666,950
Equity securities	552,566	498,382
Total assets at fair value	3,241,666	3,165,332
Fair Value Measured on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets measured at Fair Value
Equity securities	550,986	496,731
Total assets at fair value	550,986	496,731
Fair Value Measured on Recurring Basis | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	2,636,634	2,613,296
Equity securities		39
Total assets at fair value	2,636,634	2,613,335
Fair Value Measured on Recurring Basis | Significant Unobservable Inputs (Level 3)
Assets measured at Fair Value
Available-for-sale fixed income	52,466	53,654
Equity securities	1,580	1,612
Total assets at fair value	54,046	55,266
Fair Value Measured on Recurring Basis | U.S. government
Assets measured at Fair Value
Available-for-sale fixed income	315,976	454,021
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	315,976	454,021
Fair Value Measured on Recurring Basis | U.S. Agency
Assets measured at Fair Value
Available-for-sale fixed income	43,719	73,063
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	43,719	73,063
Fair Value Measured on Recurring Basis | Non-U.S. government & agency
Assets measured at Fair Value
Available-for-sale fixed income	3,960	5,847
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	3,960	5,847
Fair Value Measured on Recurring Basis | Agency MBS
Assets measured at Fair Value
Available-for-sale fixed income	372,030	331,806
Fair Value Measured on Recurring Basis | Agency MBS | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	372,030	331,806
Fair Value Measured on Recurring Basis | ABS/CMBS/MBS
Assets measured at Fair Value
Available-for-sale fixed income	252,330	240,736
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	252,330	240,736
Fair Value Measured on Recurring Basis | Corporate Debt
Assets measured at Fair Value
Available-for-sale fixed income	1,147,504	1,034,330
Fair Value Measured on Recurring Basis | Corporate Debt | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	1,095,038	980,676
Fair Value Measured on Recurring Basis | Corporate Debt | Significant Unobservable Inputs (Level 3)
Assets measured at Fair Value
Available-for-sale fixed income	52,466	53,654
Fair Value Measured on Recurring Basis | Municipal
Assets measured at Fair Value
Available-for-sale fixed income	553,581	527,147
Fair Value Measured on Recurring Basis | Municipal | Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Available-for-sale fixed income	$ 553,581	$ 527,147

Investments - Summary of Change

Investments - Summary of Changes in Balance of Level 3 securities (Details) - Significant Unobservable Inputs (Level 3) $ in Thousands	6 Months Ended
	Jun. 30, 2023 USD ($)
Summary of changes in Level 3 securities
Beginning balance	$ 55,266
Included in other comprehensive earnings (loss)	551
Sales / Calls / Maturities	(1,771)
Ending balance	54,046
Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - OCI	$ 551

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Value of Available-for-sale Fixed Income Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 195,245
Due after one year through five years	910,005
Due after five years through 10 years	567,327
Due after 10 years	573,985
ABS/CMBS/MBS	700,358
Total available-for-sale	2,946,920	$ 2,945,273
Fair Value
Due in one year or less	193,554
Due after one year through five years	861,351
Due after five years through 10 years	529,864
Due after 10 years	479,971
ABS/CMBS/MBS	624,360
Total available-for-sale	$ 2,689,100	$ 2,666,950

Investments - Additional Inform

Investments - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2023 USD ($) security	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Investment Holdings [Line Items]
Accrued investment income	$ 22,525		$ 21,259
Unrealized loss	260,939		280,222
Fixed Income Securities
Investment Holdings [Line Items]
Accrued investment income	$ 22,000		$ 20,000
Number of debt securities for which there is an allowance for credit losses | security	18
Losses on fixed income securities	$ 1,700	$ 100
Number of debt securities in an unrealized loss position for which an allowance for credit losses has not been recorded | security	1,474
Unrealized loss	$ 261,000
Unrealized losses as percentage of fixed income portfolio cost basis	9%
Unrealized losses relative to total invested assets (as a percent)	7%
Number of unrealized loss positions | security	1,474
Number of securities in unrealized loss positions for 12 months or longer | security	995

Investments - Amortized Cost _2

Investments - Amortized Cost and Fair Value of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	$ 2,946,920		$ 2,945,273
Allowance for Credit Losses	(434)	$ (465)	(339)	$ (292)	$ (594)	$ (441)
Gross Unrealized Gains	3,553		2,238
Gross Unrealized Losses	(260,939)		(280,222)
Fair Value	2,689,100		2,666,950
U.S. government
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	325,893		462,884
Gross Unrealized Gains			8
Gross Unrealized Losses	(9,917)		(8,871)
Fair Value	315,976		454,021
U.S. Agency
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	45,937		75,074
Gross Unrealized Gains			26
Gross Unrealized Losses	(2,218)		(2,037)
Fair Value	43,719		73,063
Non-U.S. government & agency
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	4,799		6,798
Gross Unrealized Losses	(839)		(951)
Fair Value	3,960		5,847
Agency MBS
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	414,503		373,687
Gross Unrealized Gains	206		336
Gross Unrealized Losses	(42,679)		(42,217)
Fair Value	372,030		331,806
ABS/CMBS/MBS
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	285,855		276,126
Allowance for Credit Losses	(5)		(8)
Gross Unrealized Gains	78		62
Gross Unrealized Losses	(33,598)		(35,444)
Fair Value	252,330		240,736
Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	1,227,628		1,122,097
Allowance for Credit Losses	(429)		(331)
Gross Unrealized Gains	1,872		541
Gross Unrealized Losses	(81,567)		(87,977)
Fair Value	1,147,504		1,034,330
Municipal
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	642,305		628,607
Gross Unrealized Gains	1,397		1,265
Gross Unrealized Losses	(90,121)		(102,725)
Fair Value	$ 553,581		$ 527,147

Investments - Schedule of Debt

Investments - Schedule of Debt Securities Available-for-sale Allowance for Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Investments Debt And Equity Securities [Abstract]
Beginning balance	$ 465	$ 594	$ 339	$ 441
Increase to allowance from securities for which credit losses were not previously recorded	2	149	25	223
Reduction from securities sold during the period		(433)		(433)
Reductions from intent to sell securities				(17)
Net increase (decrease) from securities that had an allowance at the beginning of the period	(33)	(18)	70	78
Ending balance	$ 434	$ 292	$ 434	$ 292

Investments - Schedule of Secur

Investments - Schedule of Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Fair value
Less than 12 months	$ 977,565	$ 1,619,637
12 months and greater	1,515,435	794,880
Total Fair Value	2,493,000	2,414,517
Amortized Cost
Amortized cost, less than 12 months	1,004,025	1,715,942
12 months and greater	1,749,914	978,797
Total Cost or Amortized Cost	2,753,939	2,694,739
Unrealized Loss
Less than 12 months	(26,460)	(96,305)
12 months and greater	(234,479)	(183,917)
Total Unrealized Loss	(260,939)	(280,222)
U.S. government
Fair value
Less than 12 months	220,227	399,361
12 months and greater	95,748	8,828
Total Fair Value	315,975	408,189
Amortized Cost
Amortized cost, less than 12 months	225,987	407,340
12 months and greater	99,905	9,720
Total Cost or Amortized Cost	325,892	417,060
Unrealized Loss
Less than 12 months	(5,760)	(7,979)
12 months and greater	(4,157)	(892)
Total Unrealized Loss	(9,917)	(8,871)
U.S. Agency
Fair value
Less than 12 months	33,951	32,987
12 months and greater	9,768	2,170
Total Fair Value	43,719	35,157
Amortized Cost
Amortized cost, less than 12 months	34,975	34,627
12 months and greater	10,962	2,567
Total Cost or Amortized Cost	45,937	37,194
Unrealized Loss
Less than 12 months	(1,024)	(1,640)
12 months and greater	(1,194)	(397)
Total Unrealized Loss	(2,218)	(2,037)
Non-U.S. government & agency
Fair value
Less than 12 months	658	3,626
12 months and greater	3,302	2,221
Total Fair Value	3,960	5,847
Amortized Cost
Amortized cost, less than 12 months	702	3,798
12 months and greater	4,097	3,000
Total Cost or Amortized Cost	4,799	6,798
Unrealized Loss
Less than 12 months	(44)	(172)
12 months and greater	(795)	(779)
Total Unrealized Loss	(839)	(951)
Agency MBS
Fair value
Less than 12 months	141,545	197,252
12 months and greater	216,878	117,851
Total Fair Value	358,423	315,103
Amortized Cost
Amortized cost, less than 12 months	146,150	212,776
12 months and greater	254,952	144,544
Total Cost or Amortized Cost	401,102	357,320
Unrealized Loss
Less than 12 months	(4,605)	(15,524)
12 months and greater	(38,074)	(26,693)
Total Unrealized Loss	(42,679)	(42,217)
ABS/CMBS/MBS
Fair value
Less than 12 months	20,483	96,754
12 months and greater	219,639	136,149
Total Fair Value	240,122	232,903
Amortized Cost
Amortized cost, less than 12 months	21,028	104,724
12 months and greater	252,692	163,623
Total Cost or Amortized Cost	273,720	268,347
Unrealized Loss
Less than 12 months	(545)	(7,970)
12 months and greater	(33,053)	(27,474)
Total Unrealized Loss	(33,598)	(35,444)
Corporate Debt
Fair value
Less than 12 months	429,215	660,830
12 months and greater	607,324	323,337
Total Fair Value	1,036,539	984,167
Amortized Cost
Amortized cost, less than 12 months	441,843	697,437
12 months and greater	676,263	374,707
Total Cost or Amortized Cost	1,118,106	1,072,144
Unrealized Loss
Less than 12 months	(12,628)	(36,607)
12 months and greater	(68,939)	(51,370)
Total Unrealized Loss	(81,567)	(87,977)
Municipal
Fair value
Less than 12 months	131,486	228,827
12 months and greater	362,776	204,324
Total Fair Value	494,262	433,151
Amortized Cost
Amortized cost, less than 12 months	133,340	255,240
12 months and greater	451,043	280,636
Total Cost or Amortized Cost	584,383	535,876
Unrealized Loss
Less than 12 months	(1,854)	(26,413)
12 months and greater	(88,267)	(76,312)
Total Unrealized Loss	$ (90,121)	$ (102,725)

Investments - Unrealized Losses

Investments - Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,753,939	$ 2,694,739
Fair value
Total Fair Value	2,493,000	2,414,517
Unrealized Loss
Total Unrealized Loss	$ (260,939)	$ (280,222)
Percent to Total	100%
NAIC Rating 1 | AAA/AA/A | Aaa/Aa/A
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,269,819
Fair value
Total Fair Value	2,052,151
Unrealized Loss
Total Unrealized Loss	$ (217,668)
Percent to Total	83.40%
NAIC Rating 2 | BBB | Baa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 404,162
Fair value
Total Fair Value	366,729
Unrealized Loss
Total Unrealized Loss	$ (37,433)
Percent to Total	14.40%
NAIC Rating 3 | BB | Ba
Cost or amortized Cost
Total Cost or Amortized Cost	$ 45,298
Fair value
Total Fair Value	41,464
Unrealized Loss
Total Unrealized Loss	$ (3,834)
Percent to Total	1.50%
NAIC Rating 4 | B | B
Cost or amortized Cost
Total Cost or Amortized Cost	$ 32,264
Fair value
Total Fair Value	30,844
Unrealized Loss
Total Unrealized Loss	$ (1,420)
Percent to Total	0.50%
NAIC Rating 5 | CCC | Caa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,396
Fair value
Total Fair Value	1,812
Unrealized Loss
Total Unrealized Loss	$ (584)
Percent to Total	0.20%
NAIC Rating 6 | CC Or Lower | Ca or lower
Unrealized Loss
Percent to Total	0%

Investments - Debt and Short-te

Investments - Debt and Short-term Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Investment Holdings [Line Items]
Other investments	$ 60,907		$ 60,907		$ 47,922
Investment in federal home loan bank stock	us-gaap:AssetPledgedAsCollateralMember		us-gaap:AssetPledgedAsCollateralMember		us-gaap:AssetPledgedAsCollateralMember
Cash and Short-term Investments
Investment in unconsolidated investees	$ 55,250		$ 55,250		$ 58,275
Cash	16,707		16,707		22,818
Short-term investments	271,296		271,296		36,229
Prime Holdings Insurance Services, Inc. (Prime)
Cash and Short-term Investments
Investment in unconsolidated investees	55,000		55,000
Other Unconsolidated Investees | Maximum
Cash and Short-term Investments
Investment in unconsolidated investees	1,000		1,000
FHLBC
Investment Holdings [Line Items]
Investments pledged as collateral	56,000		56,000
Federal home loan bank borrowings fair value disclosure	50,000		50,000
Investment In Low Income Housing Tax Credit Partnerships (LIHTC)
Investment Holdings [Line Items]
Other investments	12,000		12,000		13,000
Amortization on low income housing investments	800	$ 800	1,600	$ 1,700
Total tax benefit on investments in housing tax credit partnership	800	900	1,600	1,700
Qualified affordable housing project investments, unfunded commitment	1,000		1,000
Historic tax credit partnerships (HTC)
Investment Holdings [Line Items]
Other investments	15,000		15,000
Amortization on qualifying equity investments	1,100		2,300
Total tax benefit on investments in housing tax credit partnership	1,500	$ 1,300	2,900	$ 2,600
Equity investments in tax credit structures, unfunded commitment	4,000		4,000
Cash and Short-term Investments
Investment in unconsolidated investees					11,000
Investment in Private Funds
Investment Holdings [Line Items]
Other investments	27,000		27,000		$ 28,000
Fair value investments entities that calculate net asset value per share, unfunded commitments	$ 5,000		$ 5,000

Historical Loss and LAE Devel_3

Historical Loss and LAE Development - Schedule of Reconciliation of Unpaid Losses and Settlement Expenses (LAE) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Unpaid losses and LAE at beginning of year
Gross	$ 2,315,637	$ 2,043,555
Ceded	(740,089)	(608,086)
Net	1,575,548	1,435,469
Increase (decrease) in incurred losses and LAE
Current accident year	339,951	293,158
Prior accident years	(71,520)	(69,720)
Total incurred	268,431	223,438
Loss and LAE payments for claims incurred
Current accident year	(30,978)	(21,628)
Prior accident years	(172,282)	(153,490)
Total paid	(203,260)	(175,118)
Net unpaid losses and LAE at end of year	1,640,719	1,483,789
Unpaid losses and LAE at end of year
Gross	2,361,577	2,150,519
Ceded	(720,858)	(666,730)
Net unpaid losses and LAE at end of year	$ 1,640,719	$ 1,483,789

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Tax Disclosure [Abstract]
U.S. federal tax rate	21%	21%	21%	21%
Effective income tax rate reconciliation, percent, total	19.10%	65.80%	19.40%	12.10%

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) Attributable to Income from Operations with Amounts Computed by Applying U.S. Federal Tax Rate to Pretax Income from Continuing Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reconciliation of income tax expense reported to amount computed by applying the U.S. federal tax rate
Provision for income taxes at the statutory rate	$ 20,167	$ (1,376)	$ 45,953	$ 10,914
Increase (reduction) in taxes resulting from:
Excess tax benefit on share-based compensation	(878)	(761)	(2,868)	(2,175)
Tax exempt interest income	(274)	(288)	(557)	(570)
Dividends received deduction	(209)	(163)	(433)	(434)
Tax credit	(780)	(1,461)	(1,559)	(2,922)
ESOP dividends paid deduction	(144)	(138)	(281)	(268)
Nondeductible expenses	745	258	1,346	574
Other items, net	(248)	(386)	758	1,168
Total tax expense	$ 18,379	$ (4,315)	$ 42,359	$ 6,287
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)	(0.90%)	11.60%	(1.30%)	(4.20%)
Effective rate reduction due to tax exempt interest income (as a percent)	(0.30%)	4.40%	(0.30%)	(1.10%)
Effective rate reduction due to dividend received (as a percent)	(0.20%)	2.50%	(0.20%)	(0.80%)
Effective rate reduction due to tax credit (as a percent)	(0.80%)	22.30%	(0.70%)	(5.60%)
Effective rate reduction due to dividend paid to ESOP (as a percent)	(0.20%)	2.10%	(0.10%)	(0.50%)
Effective rate reduction due to nondeductible expenses (as a percent)	0.80%	(3.90%)	0.60%	1.10%
Effective rate reduction due to other items, net (as a percent)	(0.30%)	5.80%	0.40%	2.20%
Total tax expense	19.10%	65.80%	19.40%	12.10%

Stock Based Compensation - Stoc

Stock Based Compensation - Stock Plans - Additional Information (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended		6 Months Ended		96 Months Ended
	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	May 03, 2023	May 04, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted (in shares)				144,375
Intrinsic value of options				$ 16	$ 5
RLI Corp. Long-Term Incentive Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expenses		$ 2.2	$ 2.3	4.7	3.7
Income tax benefit from stock-based compensation		0.3	$ 0.4	0.8	$ 0.6
Unrecognized stock-based compensation expense	$ 8	$ 8		$ 8
Stock-based compensation expenses, recognition period				2 years 9 months 7 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)	135,838

Stock Based Compensation - Summ

Stock Based Compensation - Summary of Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2023 USD ($) $ / shares shares	Jun. 30, 2022 USD ($)
Weighted Number of Options Outstanding
Outstanding options, Beginning Balance | shares	1,695,660
Options granted (in shares) | shares	144,375
Options exercised | shares	(199,145)
Options canceled/forfeited | shares	(1,000)
Outstanding options, Ending Balance | shares	1,639,890
Exercisable options, Ending Balance | shares	806,436
Weighted Average Exercise Price
Weighted Average Exercise Price, Outstanding options, Beginning Balance | $ / shares	$ 82.42
Weighted Average Exercise Price, Options granted | $ / shares	135.72
Weighted Average Exercise Price, Options exercised | $ / shares	56.17
Weighted Average Exercise Price, Options canceled/forfeited | $ / shares	40.61
Weighted Average Exercise Price, Outstanding options, Ending Balance | $ / shares	90.33
Weighted Average Exercise Price, Exercisable options | $ / shares	$ 75.52
Weighted Average Remaining Contractual Life
Weighted Average Remaining Contractual Life, Outstanding options	5 years 3 days
Weighted Average Remaining Contractual Life, Exercisable options	3 years 9 months 10 days
Aggregate Intrinsic Value, Options exercised | $	$ 16,000	$ 5,000
Aggregate Intrinsic Value, Outstanding options | $	75,687
Aggregate Intrinsic Value, Exercisable options | $	$ 49,154

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, 2023	Jun. 30, 2022
Weighted average grant date assumptions and weighted average fair value
Weighted-average fair value of grants	$ 26.79	$ 21.05
Risk-free interest rates	3.44%	2.84%
Dividend yield	2.29%	2.50%
Expected volatility	22.95%	22.89%
Expected option life	4 years 11 months 8 days	5 years 21 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, 2023	Jun. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of restricted stock units vested	$ 1	$ 2
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
Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period	3 years
Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period	1 year

Stock Based Compensation - Sche

Stock Based Compensation - Schedule of Restricted Stock Units Activity (Details)	6 Months Ended
	Jun. 30, 2023 $ / shares shares
Number of RSUs
RSUs Nonvested, Beginning Balance | shares	44,208
RSUs Granted | shares	19,063
RSUs Reinvested | shares	206
RSUs Vested | shares	(6,748)
RSUs Forfeited | shares	(732)
RSUs Nonvested, Ending Balance | shares	55,997
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested, Beginning Balance | $ / shares	$ 109.51
Weighted Average Grant Date Fair Value, Granted | $ / shares	136.33
Weighted Average Grant Date Fair Value, Reinvested | $ / shares	129.72
Weighted Average Grant Date Fair Value, Vested | $ / shares	118.66
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	136.58
Weighted Average Grant Date Fair Value, Nonvested, Ending Balance | $ / shares	$ 117.49

Operating Segment Information -

Operating Segment Information - Summary of Selected Information by Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenues
Net premiums earned	$ 322,280		$ 282,810		$ 630,003	$ 551,962
Net investment income	28,788		18,472		55,872	36,355
Net realized gains	5,580		12,804		20,200	18,392
Net unrealized gains (losses) on equity securities	25,214		(100,994)		40,710	(128,804)
Consolidated revenue	381,862		213,092		746,785	477,905
Net Earnings
Net underwriting income	41,201		55,956		109,091	115,434
Net investment income	28,788		18,472		55,872	36,355
Net realized gains	5,580		12,804		20,200	18,392
Net unrealized gains (losses) on equity securities	25,214		(100,994)		40,710	(128,804)
General corporate expense and interest on debt	(6,266)		(4,446)		(12,488)	(9,819)
Equity in earnings of unconsolidated investees	1,514		11,654		5,437	20,413
Earnings (loss) before income taxes	96,031		(6,554)		218,822	51,971
Income tax expense (benefit)	18,379		(4,315)		42,359	6,287
Net earnings (loss)	77,652	$ 98,811	(2,239)	$ 47,923	176,463	45,684
Casualty Segment
Revenues
Net premiums earned	187,048		177,123		373,079	348,879
Net Earnings
Net underwriting income	6,977		21,442		38,808	49,089
Property Segment
Revenues
Net premiums earned	101,841		74,690		190,608	142,130
Net Earnings
Net underwriting income	25,877		26,105		54,260	48,581
Surety Segment
Revenues
Net premiums earned	33,391		30,997		66,316	60,953
Net Earnings
Net underwriting income	$ 8,347		$ 8,409		$ 16,023	$ 17,764

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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Net premiums earned	$ 322,280	$ 282,810	$ 630,003	$ 551,962
Casualty Segment
Segment Reporting Information [Line Items]
Net premiums earned	187,048	177,123	373,079	348,879
Casualty Segment | Commercial excess and personal umbrella
Segment Reporting Information [Line Items]
Net premiums earned	69,261	62,463	136,843	122,535
Casualty Segment | General liability
Segment Reporting Information [Line Items]
Net premiums earned	26,016	25,106	51,916	48,846
Casualty Segment | Commercial transportation
Segment Reporting Information [Line Items]
Net premiums earned	25,398	23,941	50,630	47,569
Casualty Segment | Professional services
Segment Reporting Information [Line Items]
Net premiums earned	24,602	23,861	48,959	47,416
Casualty Segment | Small commercial
Segment Reporting Information [Line Items]
Net premiums earned	18,455	16,813	36,396	33,458
Casualty Segment | Executive products
Segment Reporting Information [Line Items]
Net premiums earned	6,153	7,075	12,506	13,652
Casualty Segment | Other casualty
Segment Reporting Information [Line Items]
Net premiums earned	17,163	17,864	35,829	35,403
Property Segment
Segment Reporting Information [Line Items]
Net premiums earned	101,841	74,690	190,608	142,130
Property Segment | Commercial property
Segment Reporting Information [Line Items]
Net premiums earned	60,219	38,929	109,481	72,218
Property Segment | Marine
Segment Reporting Information [Line Items]
Net premiums earned	32,412	28,178	63,048	54,907
Property Segment | Other property
Segment Reporting Information [Line Items]
Net premiums earned	9,210	7,583	18,079	15,005
Surety Segment
Segment Reporting Information [Line Items]
Net premiums earned	33,391	30,997	66,316	60,953
Surety Segment | Commercial
Segment Reporting Information [Line Items]
Net premiums earned	12,505	11,663	24,923	23,366
Surety Segment | Miscellaneous
Segment Reporting Information [Line Items]
Net premiums earned	11,887	11,587	23,934	22,940
Surety Segment | Contract
Segment Reporting Information [Line Items]
Net premiums earned	$ 8,999	$ 7,747	$ 17,459	$ 14,647

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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Leases [Abstract]
Operating lease cost	$ 1,239	$ 1,256	$ 2,508	$ 2,414
Variable lease cost	444	349	882	695
Sublease income	(139)	(139)	(277)	(277)
Total lease cost	1,544	1,466	3,113	2,832
Cash paid for amounts included in measurement of lease liabilities
Operating cash outflows from operating leases	1,357	1,278	2,755	2,600
ROU assets obtained in exchange for new operating lease liabilities	943	$ 2,431	984	2,431
Reduction to ROU assets resulting from reduction to lease liabilities			200
Other non-cash reductions to ROU assets				$ 73
Operating lease ROU assets	$ 11,185		$ 11,185		$ 12,766
Operating Lease, Right-of-Use Asset, Statement of Financial Position	Other assets		Other assets		Other assets
Operating lease liabilities	$ 12,635		$ 12,635		$ 14,499
Operating Lease, Liability, Statement of Financial Position	Other liabilities		Other liabilities		Other liabilities
Weighted-average remaining lease term - operating leases	4 years 2 months 4 days		4 years 2 months 4 days		4 years 2 months 15 days
Weighted-average discount rate - operating leases	1.97%		1.97%		2.11%

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments under Non-cancellable Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Future minimum lease payments under non-cancellable leases
2023	$ 2,636
2024	3,827
2025	2,551
2026	1,646
2027	997
2028	704
Thereafter	883
Total future minimum lease payments	13,244
Less imputed interest	(609)
Operating lease liabilities	$ 12,635	$ 14,499

Acquisitions and Dispositions (

Acquisitions and Dispositions (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2022	Mar. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Dispositions
Cash proceeds from sale			$ 14,134
Maui Jim Inc.
Dispositions
Cash proceeds from sale	$ 687,000
Maui Jim Inc. | Net Realized Gain (Loss)
Dispositions
Recognized gain on sale		$ 14,000		$ 571,000

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ 77,652	$ 98,811	$ (2,239)	$ 47,923	$ 176,463	$ 45,684

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 2023
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