W. R. Berkley (WRB) 10-Q 5 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 29, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-15202
Entity Registrant Name	W. R. BERKLEY CORP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-1867895
Entity Address, Address Line One	475 Steamboat Road
Entity Address, City or Town	Greenwich
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06830
City Area Code	(203)
Local Phone Number	629-3000
Title of 12(b) Security	Common Stock, par value $.20 per share
Trading Symbol	WRB
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		177,380,548
Entity Central Index Key	0000011544
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
5.75% Subordinated Debentures due 2056
Entity Information [Line Items]
Title of 12(b) Security	5.75% Subordinated Debentures due 2056
Trading Symbol	WRB-PD
Security Exchange Name	NYSE
5.70% Subordinated Debentures due 2058
Entity Information [Line Items]
Title of 12(b) Security	5.70% Subordinated Debentures due 2058
Trading Symbol	WRB-PE
Security Exchange Name	NYSE
5.10% Subordinated Debentures due 2059
Entity Information [Line Items]
Title of 12(b) Security	5.10% Subordinated Debentures due 2059
Trading Symbol	WRB-PF
Security Exchange Name	NYSE
4.25% Subordinated Debentures due 2060
Entity Information [Line Items]
Title of 12(b) Security	4.25% Subordinated Debentures due 2060
Trading Symbol	WRB-PG
Security Exchange Name	NYSE
4.125% Subordinated Debentures due 2061
Entity Information [Line Items]
Title of 12(b) Security	4.125% Subordinated Debentures due 2061
Trading Symbol	WRB-PH
Security Exchange Name	NYSE

Consolidated Balance Sheets Con

Consolidated Balance Sheets Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments:
Fixed maturity securities (amortized cost of $15,126,980 and $13,755,858; allowance for expected credit losses of $20,739 and $2,580 at March 31, 2021 and December 31, 2020, respectively)	$ 15,400,118	$ 14,159,369
Real estate	1,961,212	1,960,914
Investment funds	1,358,997	1,309,430
Arbitrage trading account	614,721	341,473
Equity securities	621,629	625,667
Loans receivable (net of allowance for expected credit losses of $4,198 and $5,437 at March 31, 2021 and December 31, 2020, respectively)	76,896	84,913
Total investments	20,033,573	18,481,766
Cash and cash equivalents	2,014,911	2,372,366
Premiums and fees receivable (net of allowance for expected credit losses of $24,264 and $22,883 at March 31, 2021 and December 31, 2020, respectively)	2,260,026	2,167,799
Due from reinsurers (net of allowance for expected credit losses of $7,373 and $7,801 at March 31, 2021 and December 31, 2020, respectively)	2,549,739	2,424,502
Deferred policy acquisition costs	594,309	556,168
Prepaid reinsurance premiums	668,111	648,376
Trading account receivables from brokers and clearing organizations	257,756	524,727
Property, furniture and equipment	404,281	405,930
Goodwill	169,652	169,652
Accrued investment income	123,755	120,464
Other assets	715,161	700,215
Total assets	29,791,274	28,571,965
Liabilities:
Reserves for losses and loss expenses	14,080,528	13,784,430
Unearned premiums	4,288,252	4,073,191
Due to reinsurers	463,467	426,124
Trading account securities sold but not yet purchased	218	10,048
Current and deferred federal and foreign income taxes	76,667	48,495
Other liabilities	1,141,444	1,178,546
Senior notes and other debt	2,021,142	1,623,025
Subordinated debentures	1,289,272	1,102,309
Total liabilities	23,360,990	22,246,168
Equity:
Perferred stock, par value $.10 per share: Authorized 5,000,000 shares; issued and outstanding - none	0	0
Common stock, par value $.20 per share: Authorized 500,000,000 shares, issued and outstanding, net of treasury shares, 177,930,502 and 183,411,907 shares, respectively	70,535	70,535
Additional paid-in capital	1,023,556	1,012,483
Retained earnings	8,556,621	8,348,381
Accumulated other comprehensive loss	(148,252)	(62,172)
Treasury stock, at cost, 175,303,557 and 174,851,350 shares, respectively	(3,087,860)	(3,058,425)
Total stockholders’ equity	6,414,600	6,310,802
Noncontrolling interests	15,684	14,995
Total equity	6,430,284	6,325,797
Total liabilities and equity	$ 29,791,274	$ 28,571,965

Consolidated Balance Sheets C_2

Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Fixed maturity securities, allowance for credit loss	$ 20,739	$ 2,580
Fixed maturity securities, amortized cost	15,126,980	13,755,858
Cumulative effect adjustment resulting from changes in accounting principles	4,198	5,437
Cumulative effect adjustment resulting from changes in accounting principles	24,264	22,883
Reinsurance recoverable, allowance for credit loss	$ 7,373	$ 7,801
Preferred stock, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred stock issued (in shares)	5,000,000	5,000,000
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollar per share)	$ 0.20	$ 0.20
Common shares authorized (in shares)	500,000,000	500,000,000
Common shares issued (in shares)	177,372,943	177,825,150
Common shares outstanding (in shares)	177,372,943	177,825,150
Treasury stock issued at cost (in shares)	175,303,557	174,851,350

Consolidated Statements Income

Consolidated Statements Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
REVENUES:
Net premiums written	$ 2,050,038	$ 1,845,846
Change in net unearned premiums	(200,082)	(154,428)
Net premiums earned	1,849,956	1,691,418
Net investment income	158,577	174,763
Net realized and unrealized gains (losses) on investments	51,759	(143,285)
Change in allowance for expected credit losses on investments	(16,920)	(33,889)
Net investment gains (losses)	34,839	(177,174)
Revenues from non-insurance businesses	87,430	93,729
Insurance service fees	25,808	25,751
Other income	259	2,123
Total revenues	2,156,869	1,810,610
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	1,121,592	1,107,253
Other operating costs and expenses	616,268	578,334
Expenses from non-insurance businesses	86,290	94,757
Interest expense	36,651	36,734
Total operating costs and expenses	1,860,801	1,817,078
Income (loss) before income taxes	296,068	(6,468)
Income tax (expense) benefit	(64,352)	2,942
Net income (loss) before noncontrolling interests	231,716	(3,526)
Noncontrolling interests	(2,191)	(892)
Net income (loss) to common stockholders	$ 229,525	$ (4,418)
NET INCOME (LOSS) PER SHARE:
Basic (in dollar per share)	$ 1.24	$ (0.02)
Diluted (in dollar per share)	$ 1.23	$ (0.02)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss) before noncontrolling interests	$ 231,716	$ (3,526)
Other comprehensive loss:
Change in unrealized currency translation adjustments	4,050	(98,194)
Change in unrealized investment gains, net of taxes	(90,130)	(258,981)
Other comprehensive loss	(86,080)	(357,175)
Comprehensive income (loss)	145,636	(360,701)
Noncontrolling interests	(2,191)	(893)
Comprehensive income (loss) to common stockholders	$ 143,445	$ (361,594)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated Other Comprehensive Income (Loss)	Unrealized investment gain	Currency Translation Adjustments	Treasury stock	Noncontrolling interest	Cumulative effect adjustment resulting from changes in accounting principlesRetained earnings	Cumulative effect adjustment resulting from changes in accounting principlesAccumulated Other Comprehensive Income (Loss)	Cumulative effect adjustment resulting from changes in accounting principlesUnrealized investment gain	Cumulative effect adjustment resulting from changes in accounting principlesCurrency Translation Adjustments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment resulting from changes in accounting principles		$ 70,535	$ 1,056,042	$ 7,932,372	$ (257,299)	$ 124,514	$ (381,813)	$ (2,726,711)	$ 43,403	$ (30,514)		$ 24,952
Beginning of period at Dec. 31, 2019		70,535	1,056,042	7,932,372	(257,299)	124,514	(381,813)	(2,726,711)	43,403	(30,514)		24,952
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(4,590)
Restricted stock units expensed			11,632
Cumulative effect adjustment resulting from changes in accounting principles		70,535	1,063,084	7,877,371	(589,521)	(109,514)	(480,007)	(2,927,994)	44,069	(30,514)		24,952
Net income (loss) before noncontrolling interests	$ (3,526)			(4,418)					892
Dividends ($0.12 and $0.11 per share, respectively)				(20,069)
Change in unrealized gains on securities without an allowance for expected credit losses	(258,981)					(260,521)
Change in unrealized gains on securities with an allowance for expected credit losses						1,541
Net change in period	(98,194)						(98,194)
Stock exercised/vested								1,338
Stock repurchased								(202,621)
Distributions									(227)
Other comprehensive income, net of tax	$ (357,175)				(357,175)		(98,194)		1
End of period at Mar. 31, 2020			1,063,084	7,877,371	(589,521)	(109,514)	(480,007)	(2,927,994)	44,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.11
Cumulative effect adjustment resulting from changes in accounting principles			1,063,084	7,877,371	(589,521)	(109,514)	(480,007)	(2,927,994)	44,069
Cumulative effect adjustment resulting from changes in accounting principles	$ 6,325,797	70,535	1,012,483	8,348,381	(62,172)	289,714	(351,886)	(3,058,425)	14,995	0	$ 24,952	0	$ 0
Beginning of period at Dec. 31, 2020	6,325,797	70,535	1,012,483	8,348,381	(62,172)	289,714	(351,886)	(3,058,425)	14,995	0	24,952	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(525)
Restricted stock units expensed			11,598
Cumulative effect adjustment resulting from changes in accounting principles	6,325,797	$ 70,535	1,023,556	8,556,621	(62,172)	199,584	(351,886)	(3,087,860)	15,684	$ 0	$ 24,952	$ 0	$ 0
Net income (loss) before noncontrolling interests	231,716			229,525					2,191
Dividends ($0.12 and $0.11 per share, respectively)				(21,285)
Change in unrealized gains on securities without an allowance for expected credit losses	(90,130)					(100,485)
Change in unrealized gains on securities with an allowance for expected credit losses						10,355
Net change in period	4,050						4,050
Stock exercised/vested								248
Stock repurchased								(29,683)
Distributions									(1,502)
Other comprehensive income, net of tax	(86,080)				(86,080)		4,050		0
End of period at Mar. 31, 2021	$ 6,430,284		1,023,556	8,556,621	(148,252)	199,584	(347,836)	(3,087,860)	15,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.12
Cumulative effect adjustment resulting from changes in accounting principles	$ 6,430,284		$ 1,023,556	$ 8,556,621	$ (148,252)	$ 199,584	$ (347,836)	$ (3,087,860)	$ 15,684

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FROM OPERATING ACTIVITIES:
Net income (loss) to common stockholders	$ 229,525	$ (4,418)
Adjustments to reconcile net income (loss) to net cash from operating activities:
Net investment (gains) losses	(34,839)	177,174
Depreciation and amortization	33,543	25,063
Noncontrolling interests	2,191	892
Investment funds	(38,935)	(40,576)
Stock incentive plans	11,817	11,683
Change in:
Arbitrage trading account	(16,108)	2,455
Premiums and fees receivable	(96,290)	(97,169)
Reinsurance accounts	(105,589)	(43,104)
Deferred policy acquisition costs	(38,577)	(26,139)
Income taxes	47,372	(12,500)
Reserves for losses and loss expenses	303,305	200,294
Unearned premiums	219,920	163,793
Other	(206,345)	(204,878)
Net cash from operating activities	310,990	152,570
CASH (USED IN) FROM INVESTING ACTIVITIES:
Proceeds from sale of fixed maturity securities	1,115,114	1,574,232
Proceeds from sale of equity securities	57,457	5,311
Distributions from investment funds	36,236	99,194
Proceeds from maturities and prepayments of fixed maturity securities	1,623,357	1,055,722
Purchase of fixed maturity securities	(4,118,161)	(2,598,076)
Purchase of equity securities	(69,181)	(35,260)
Real estate sold (purchased)	9,787	(24,249)
Change in loans receivable	9,256	2,877
Net purchases of property, furniture and equipment	(10,872)	(14,637)
Change in balances due to security brokers	151,776	(34,378)
Other	0	86
Net cash (used in) from investing activities	(1,195,231)	30,822
CASH FROM (USED IN) FINANCING ACTIVITIES:
Repayment of senior notes and other debt	(110,000)	0
Net payments for stock options exercised	(525)	(3,321)
Net proceeds from issuance of debt	691,213	4,259
Cash dividends to common stockholders	(21,285)	(20,069)
Purchase of common treasury shares	(29,683)	(202,621)
Other, net	(1,503)	(204)
Net cash from (used in) financing activities	528,217	(221,956)
Net impact on cash due to change in foreign exchange rates	(1,431)	(20,134)
Net change in cash and cash equivalents	(357,455)	(58,698)
Cash and cash equivalents at beginning of year	2,372,366	1,023,710
Cash and cash equivalents at end of period	$ 2,014,911	$ 965,012

Statements of Cash Flows

Statements of Cash Flows	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Statements of Cash Flows	Statements of Cash Flows    Interest payments were $45,393,000 and $54,582,000 for the three months ended March 31, 2021 and 2020, respectively. No income taxes were paid during such periods.

General

General	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	General The unaudited consolidated financial statements, which include the accounts of W. R. Berkley Corporation and its subsidiaries (the “Company”), have been prepared on the basis of U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all the information and notes required by GAAP for annual financial statements. The unaudited consolidated financial statements reflect all adjustments, consisting only of normal recurring items, which are necessary to present fairly the Company’s financial position and results of operations on a basis consistent with the prior audited consolidated financial statements. Operating results for interim periods are not necessarily indicative of the results that may be expected for the year. All significant intercompany accounts and transactions have been eliminated. Reclassifications have been made in the 2020 financial statements as originally reported to conform to the presentation of the 2021 financial statements. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the revenues and expenses reflected during the reporting period. For further information related to areas of judgment and estimates and other information necessary to understand the Company’s financial position and results of operations, refer to the audited consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. The income tax provision has been computed based on the Company’s estimated annual effective tax rate. The effective income tax rate differs from the federal income tax rate of 21% principally because of state and foreign income taxes, which was partially offset by tax-exempt investment income and tax benefits related to equity-based compensation.

Per Share Data

Per Share Data	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Per Share Data	Per Share Data The Company presents both basic and diluted net income (loss) per share (“EPS”) amounts. Basic EPS is calculated by dividing net income (loss) by the weighted average number of common shares outstanding during the period (including 7,767,874 and 7,575,168 common shares held in a grantor trust as of March 31, 2021 and 2020, respectively). The common shares held in the grantor trust are for delivery upon settlement of vested but mandatorily deferred restricted stock units ("RSUs"). Shares held by the grantor trust do not affect diluted shares outstanding since the shares deliverable under vested RSUs were already included in diluted shares outstanding. Diluted EPS is based upon the weighted average number of basic and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. For the period ended March 31, 2020, diluted shares have been reduced by 2.0 million to reflect the anti-dilutive effect of common equivalent shares. The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows: For the Three Months (In thousands) 2021 2020 Basic 185,195 190,287 Diluted 186,830 190,287

Recent Accounting Pronouncement

Recent Accounting Pronouncements and Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Recent Accounting Pronouncements and Accounting Policies	Recent Accounting Pronouncements and Accounting Policies Recently adopted accounting pronouncements: All accounting and reporting standards that have become effective in 2021 were either not applicable to the Company or their adoption did not have a material impact on the Company. Accounting and reporting standards that are not yet effective: All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Consolidated Statements of Comprehensive Income	Consolidated Statements of Comprehensive Income (Loss) The following table presents the components of the changes in accumulated other comprehensive income (loss) ("AOCI"): (In thousands) Unrealized Investment Gains (Losses) Currency Translation Adjustments Accumulated Other Comprehensive As of and for the three months ended March 31, 2021 Changes in AOCI Beginning of period $ 289,714 $ (351,886) $ (62,172) Other comprehensive (loss) income before reclassifications (98,991) 4,050 (94,941) Amounts reclassified from AOCI 8,861 — 8,861 Other comprehensive (loss) income (90,130) 4,050 (86,080) Unrealized investment gain related to noncontrolling interest — — — End of period $ 199,584 $ (347,836) $ (148,252) Amounts reclassified from AOCI Pre-tax $ 11,216 (1) $ — $ 11,216 Tax effect (2,355) (2) — (2,355) After-tax amounts reclassified $ 8,861 $ — $ 8,861 Other comprehensive (loss) income Pre-tax $ (113,735) $ 4,050 $ (109,685) Tax effect 23,605 — 23,605 Other comprehensive (loss) income $ (90,130) $ 4,050 $ (86,080) As of and for the three months ended March 31, 2020 Changes in AOCI Beginning of period $ 124,514 $ (381,813) $ (257,299) Cumulative effect adjustment resulting from changes in accounting principles 24,952 — 24,952 Restated beginning of period 149,466 (381,813) (232,347) Other comprehensive loss before reclassifications (298,531) (98,194) (396,725) Amounts reclassified from AOCI 39,550 — 39,550 Other comprehensive loss (258,981) (98,194) (357,175) Unrealized investment loss related to noncontrolling interest 1 — 1 End of period $ (109,514) $ (480,007) $ (589,521) Amounts reclassified from AOCI Pre-tax $ 50,063 (1) $ — $ 50,063 Tax effect (10,513) (2) — (10,513) After-tax amounts reclassified $ 39,550 $ — $ 39,550 Other comprehensive loss Pre-tax $ (332,850) $ (98,194) $ (431,044) Tax effect 73,869 — 73,869 Other comprehensive loss $ (258,981) $ (98,194) $ (357,175) ____________ (1) Net investment gains (losses) in the consolidated statements of income (loss). (2) Income tax (expense) benefit in the consolidated statements of income (loss).

Investments In Fixed Maturity S

Investments In Fixed Maturity Securities	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investments In Fixed Maturity Securities	Investments in Fixed Maturity Securities At March 31, 2021 and December 31, 2020, investments in fixed maturity securities were as follows: (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses March 31, 2021 Held to maturity: State and municipal $ 67,710 $ (730) $ 11,150 $ — $ 78,130 $ 66,980 Residential mortgage-backed 6,101 — 924 — 7,025 6,101 Total held to maturity 73,811 (730) 12,074 — 85,155 73,081 Available for sale: U.S. government and government agency 541,180 — 15,449 (915) 555,714 555,714 State and municipal: Special revenue 2,112,542 — 78,450 (3,284) 2,187,708 2,187,708 State general obligation 399,636 — 28,156 (1,059) 426,733 426,733 Pre-refunded 231,235 — 17,990 (465) 248,760 248,760 Corporate backed 164,542 — 8,585 (788) 172,339 172,339 Local general obligation 432,788 — 34,850 (585) 467,053 467,053 Total state and municipal 3,340,743 — 168,031 (6,181) 3,502,593 3,502,593 Mortgage-backed securities: Residential 889,638 — 19,315 (12,215) 896,738 896,738 Commercial 172,817 — 6,555 (86) 179,286 179,286 Total mortgage-backed securities 1,062,455 — 25,870 (12,301) 1,076,024 1,076,024 Asset-backed 3,952,009 — 10,789 (18,160) 3,944,638 3,944,638 Corporate: Industrial 2,986,688 (16) 88,810 (14,819) 3,060,663 3,060,663 Financial 1,517,251 — 48,756 (1,638) 1,564,369 1,564,369 Utilities 426,213 — 15,476 (2,360) 439,329 439,329 Other 153,700 — 429 (301) 153,828 153,828 Total corporate 5,083,852 (16) 153,471 (19,118) 5,218,189 5,218,189 Foreign government 1,072,930 (19,993) 19,361 (42,419) 1,029,879 1,029,879 Total available for sale 15,053,169 (20,009) 392,971 (99,094) 15,327,037 15,327,037 Total investments in fixed maturity securities $ 15,126,980 $ (20,739) $ 405,045 $ (99,094) $ 15,412,192 $ 15,400,118 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income (loss). Amount excludes unrealized losses relating to non-credit factors. (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses December 31, 2020 Held to maturity: State and municipal $ 67,117 $ (798) $ 13,217 $ — $ 79,536 $ 66,319 Residential mortgage-backed 6,455 — 1,043 — 7,498 6,455 Total held to maturity 73,572 (798) 14,260 — 87,034 72,774 Available for sale: U.S. government and government agency 586,020 — 18,198 (347) 603,871 603,871 State and municipal: Special revenue 2,137,162 — 96,924 (714) 2,233,372 2,233,372 State general obligation 417,397 — 33,407 — 450,804 450,804 Pre-refunded 250,081 — 21,472 (162) 271,391 271,391 Corporate backed 206,356 — 8,755 (638) 214,473 214,473 Local general obligation 410,583 — 40,596 (555) 450,624 450,624 Total state and municipal 3,421,579 — 201,154 (2,069) 3,620,664 3,620,664 Mortgage-backed securities: Residential 813,187 — 24,664 (5,238) 832,613 832,613 Commercial 181,105 — 6,725 (113) 187,717 187,717 Total mortgage-backed securities 994,292 — 31,389 (5,351) 1,020,330 1,020,330 Asset-backed 3,218,048 — 10,035 (33,497) 3,194,586 3,194,586 Corporate: Industrial 2,456,516 (518) 115,926 (7,449) 2,564,475 2,564,475 Financial 1,513,943 — 62,947 (987) 1,575,903 1,575,903 Utilities 389,267 — 31,931 (33) 421,165 421,165 Other 109,353 — 696 (11) 110,038 110,038 Total corporate 4,469,079 (518) 211,500 (8,480) 4,671,581 4,671,581 Foreign government 993,268 (1,264) 28,007 (44,448) 975,563 975,563 Total available for sale 13,682,286 (1,782) 500,283 (94,192) 14,086,595 14,086,595 Total investments in fixed maturity securities $ 13,755,858 $ (2,580) $ 514,543 $ (94,192) $ 14,173,629 $ 14,159,369 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses, excluding the cumulative effect adjustment resulting from changes in accounting principles, is recognized in the consolidated statements of income (loss). Amount excludes unrealized losses relating to non-credit factors. The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2021: State and Municipal (In thousands) Allowance for expected credit losses at December 31, 2020 $ 798 Provision for expected credit losses (68) Allowance for expected credit losses at March 31, 2021 $ 730 The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2020: State and Municipal (In thousands) Allowance for expected credit losses at January 1, 2020 $ — Cumulative effect adjustment resulting from changes in accounting principles 69 Provision for expected credit losses 38 Allowance for expected credit losses at March 31, 2020 $ 107 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2021: Foreign Government Corporate Total (In thousands) Allowance for expected credit losses at December 31, 2020 $ 1,264 $ 518 $ 1,782 Expected credit losses on securities for which credit losses were not previously recorded 18,990 16 19,006 Expected credit losses on securities for which credit losses were previously recorded (261) (513) (774) Reduction due to disposals — (5) (5) Allowance for expected credit losses at March 31, 2021 $ 19,993 $ 16 $ 20,009 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2020: Foreign Government Corporate Total (In thousands) Allowance for expected credit losses at January 1, 2020 $ — $ — $ — Cumulative effect adjustment resulting from changes in accounting principles 35,645 — 35,645 Expected credit losses on securities for which credit losses were not previously recorded 12,494 6,436 18,930 Expected credit losses on securities for which credit losses were previously recorded 16,369 — 16,369 Reduction due to disposals (3,588) — (3,588) Allowance for expected credit losses at March 31, 2020 $ 60,920 $ 6,436 $ 67,356 During the three months ended March 31, 2021, the Company increased the allowance for expected credit losses for available for sale securities utilizing its credit loss assessment process and inputs used in its credit loss model, primarily due to foreign government securities that had no reserve in prior periods. During the three months ended March 31, 2020, the Company increased the allowance for expected credit losses for available for sale securities primarily due to the negative impact to the financial markets caused by COVID-19. The amortized cost and fair value of fixed maturity securities at March 31, 2021, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations. (In thousands) Amortized Fair Due in one year or less $ 1,778,569 $ 1,765,769 Due after one year through five years 6,419,223 6,576,943 Due after five years through ten years 3,500,751 3,592,140 Due after ten years 2,359,151 2,394,291 Mortgage-backed securities 1,068,556 1,083,049 Total $ 15,126,250 $ 15,412,192 ________________ (1) Amortized cost is reduced by the allowance for expected credit losses of $730 thousand related to held to maturity securities.

Investments in Equity Securitie

Investments in Equity Securities	3 Months Ended
	Mar. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Investments in Equity Securities	Investments in Fixed Maturity Securities At March 31, 2021 and December 31, 2020, investments in fixed maturity securities were as follows: (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses March 31, 2021 Held to maturity: State and municipal $ 67,710 $ (730) $ 11,150 $ — $ 78,130 $ 66,980 Residential mortgage-backed 6,101 — 924 — 7,025 6,101 Total held to maturity 73,811 (730) 12,074 — 85,155 73,081 Available for sale: U.S. government and government agency 541,180 — 15,449 (915) 555,714 555,714 State and municipal: Special revenue 2,112,542 — 78,450 (3,284) 2,187,708 2,187,708 State general obligation 399,636 — 28,156 (1,059) 426,733 426,733 Pre-refunded 231,235 — 17,990 (465) 248,760 248,760 Corporate backed 164,542 — 8,585 (788) 172,339 172,339 Local general obligation 432,788 — 34,850 (585) 467,053 467,053 Total state and municipal 3,340,743 — 168,031 (6,181) 3,502,593 3,502,593 Mortgage-backed securities: Residential 889,638 — 19,315 (12,215) 896,738 896,738 Commercial 172,817 — 6,555 (86) 179,286 179,286 Total mortgage-backed securities 1,062,455 — 25,870 (12,301) 1,076,024 1,076,024 Asset-backed 3,952,009 — 10,789 (18,160) 3,944,638 3,944,638 Corporate: Industrial 2,986,688 (16) 88,810 (14,819) 3,060,663 3,060,663 Financial 1,517,251 — 48,756 (1,638) 1,564,369 1,564,369 Utilities 426,213 — 15,476 (2,360) 439,329 439,329 Other 153,700 — 429 (301) 153,828 153,828 Total corporate 5,083,852 (16) 153,471 (19,118) 5,218,189 5,218,189 Foreign government 1,072,930 (19,993) 19,361 (42,419) 1,029,879 1,029,879 Total available for sale 15,053,169 (20,009) 392,971 (99,094) 15,327,037 15,327,037 Total investments in fixed maturity securities $ 15,126,980 $ (20,739) $ 405,045 $ (99,094) $ 15,412,192 $ 15,400,118 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income (loss). Amount excludes unrealized losses relating to non-credit factors. (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses December 31, 2020 Held to maturity: State and municipal $ 67,117 $ (798) $ 13,217 $ — $ 79,536 $ 66,319 Residential mortgage-backed 6,455 — 1,043 — 7,498 6,455 Total held to maturity 73,572 (798) 14,260 — 87,034 72,774 Available for sale: U.S. government and government agency 586,020 — 18,198 (347) 603,871 603,871 State and municipal: Special revenue 2,137,162 — 96,924 (714) 2,233,372 2,233,372 State general obligation 417,397 — 33,407 — 450,804 450,804 Pre-refunded 250,081 — 21,472 (162) 271,391 271,391 Corporate backed 206,356 — 8,755 (638) 214,473 214,473 Local general obligation 410,583 — 40,596 (555) 450,624 450,624 Total state and municipal 3,421,579 — 201,154 (2,069) 3,620,664 3,620,664 Mortgage-backed securities: Residential 813,187 — 24,664 (5,238) 832,613 832,613 Commercial 181,105 — 6,725 (113) 187,717 187,717 Total mortgage-backed securities 994,292 — 31,389 (5,351) 1,020,330 1,020,330 Asset-backed 3,218,048 — 10,035 (33,497) 3,194,586 3,194,586 Corporate: Industrial 2,456,516 (518) 115,926 (7,449) 2,564,475 2,564,475 Financial 1,513,943 — 62,947 (987) 1,575,903 1,575,903 Utilities 389,267 — 31,931 (33) 421,165 421,165 Other 109,353 — 696 (11) 110,038 110,038 Total corporate 4,469,079 (518) 211,500 (8,480) 4,671,581 4,671,581 Foreign government 993,268 (1,264) 28,007 (44,448) 975,563 975,563 Total available for sale 13,682,286 (1,782) 500,283 (94,192) 14,086,595 14,086,595 Total investments in fixed maturity securities $ 13,755,858 $ (2,580) $ 514,543 $ (94,192) $ 14,173,629 $ 14,159,369 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses, excluding the cumulative effect adjustment resulting from changes in accounting principles, is recognized in the consolidated statements of income (loss). Amount excludes unrealized losses relating to non-credit factors. The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2021: State and Municipal (In thousands) Allowance for expected credit losses at December 31, 2020 $ 798 Provision for expected credit losses (68) Allowance for expected credit losses at March 31, 2021 $ 730 The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2020: State and Municipal (In thousands) Allowance for expected credit losses at January 1, 2020 $ — Cumulative effect adjustment resulting from changes in accounting principles 69 Provision for expected credit losses 38 Allowance for expected credit losses at March 31, 2020 $ 107 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2021: Foreign Government Corporate Total (In thousands) Allowance for expected credit losses at December 31, 2020 $ 1,264 $ 518 $ 1,782 Expected credit losses on securities for which credit losses were not previously recorded 18,990 16 19,006 Expected credit losses on securities for which credit losses were previously recorded (261) (513) (774) Reduction due to disposals — (5) (5) Allowance for expected credit losses at March 31, 2021 $ 19,993 $ 16 $ 20,009 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2020: Foreign Government Corporate Total (In thousands) Allowance for expected credit losses at January 1, 2020 $ — $ — $ — Cumulative effect adjustment resulting from changes in accounting principles 35,645 — 35,645 Expected credit losses on securities for which credit losses were not previously recorded 12,494 6,436 18,930 Expected credit losses on securities for which credit losses were previously recorded 16,369 — 16,369 Reduction due to disposals (3,588) — (3,588) Allowance for expected credit losses at March 31, 2020 $ 60,920 $ 6,436 $ 67,356 During the three months ended March 31, 2021, the Company increased the allowance for expected credit losses for available for sale securities utilizing its credit loss assessment process and inputs used in its credit loss model, primarily due to foreign government securities that had no reserve in prior periods. During the three months ended March 31, 2020, the Company increased the allowance for expected credit losses for available for sale securities primarily due to the negative impact to the financial markets caused by COVID-19. The amortized cost and fair value of fixed maturity securities at March 31, 2021, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations. (In thousands) Amortized Fair Due in one year or less $ 1,778,569 $ 1,765,769 Due after one year through five years 6,419,223 6,576,943 Due after five years through ten years 3,500,751 3,592,140 Due after ten years 2,359,151 2,394,291 Mortgage-backed securities 1,068,556 1,083,049 Total $ 15,126,250 $ 15,412,192 ________________ (1) Amortized cost is reduced by the allowance for expected credit losses of $730 thousand related to held to maturity securities.
Real estate
Debt Securities, Available-for-sale [Line Items]
Investments in Equity Securities	Investments in Equity Securities At March 31, 2021 and December 31, 2020, investments in equity securities were as follows: (In thousands) Cost Gross Unrealized Fair Carrying Gains Losses March 31, 2021 Common stocks $ 339,742 $ 60,766 $ (8,345) $ 392,163 $ 392,163 Preferred stocks 196,569 33,523 (626) 229,466 229,466 Total $ 536,311 $ 94,289 $ (8,971) $ 621,629 $ 621,629 December 31, 2020 Common stocks $ 335,617 $ 28,742 $ (14,178) $ 350,181 $ 350,181 Preferred stocks 180,397 95,581 (492) 275,486 275,486 Total $ 516,014 $ 124,323 $ (14,670) $ 625,667 $ 625,667

Arbitrage Trading Account

Arbitrage Trading Account	3 Months Ended
	Mar. 31, 2021
Debt Securities, Trading, and Equity Securities, FV-NI [Abstract]
Arbitrage Trading Account	Arbitrage Trading Account At March 31, 2021 and December 31, 2020, the fair and carrying values of the arbitrage trading account were $615 million and $341 million, respectively. The primary focus of the trading account is merger arbitrage. Merger arbitrage is the business of investing in the securities of publicly held companies which are the targets in announced tender offers and mergers. Arbitrage investing differs from other types of investing in its focus on transactions and events believed likely to bring about a change in value over a relatively short time period (usually four months or less). The Company uses put options and call options in order to mitigate the impact of potential changes in market conditions on the merger arbitrage trading account. These options are reported at fair value. As of March 31, 2021, the fair value of short option contracts outstanding was $161 thousand (notional amount of $18.5 million). Other than with respect to the use of these trading account securities, the Company does not make use of derivatives.

Net Investment Income

Net Investment Income	3 Months Ended
	Mar. 31, 2021
Net Investment Income [Abstract]
Net Investment Income	Net Investment Income Net investment income consisted of the following: For the Three Months (In thousands) 2021 2020 Investment income earned on: Fixed maturity securities, including cash and cash equivalents and loans receivable $ 94,677 $ 128,018 Investment funds 38,935 40,577 Arbitrage trading account 19,074 1,138 Equity securities 6,180 1,563 Real estate 1,161 6,096 Gross investment income 160,027 177,392 Investment expense (1,450) (2,629) Net investment income $ 158,577 $ 174,763

Investment Funds

Investment Funds	3 Months Ended
	Mar. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Investment Funds	Investment Funds The Company evaluates whether it is an investor in a variable interest entity ("VIE"). Such entities do not have sufficient equity at risk to finance their activities without additional subordinated financial support, or the equity investors, as a group, do not have the characteristics of a controlling financial interest (primary beneficiary). The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE's capital structure, contractual terms, nature of the VIE's operations and purpose, and the Company's relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE and on an ongoing basis. The Company is not the primary beneficiary in any of its investment funds, and accordingly, carries its interests in investment funds under the equity method of accounting. The Company’s maximum exposure to loss with respect to these investments is limited to the carrying amount reported on the Company’s consolidated balance sheet and its unfunded commitments, which were $129 million as of March 31, 2021. Investment funds consisted of the following: Carrying Value as of Income from March 31, December 31, For the Three Months (In thousands) 2021 2020 2021 2020 Financial services $ 477,927 $ 434,437 $ 17,142 $ 15,209 Real Estate 304,461 310,783 4,434 6,790 Energy 143,852 140,935 3,320 4,413 Transportation 193,401 190,125 6,228 2,646 Other funds 239,356 233,150 7,811 11,519 Total $ 1,358,997 $ 1,309,430 $ 38,935 $ 40,577 The Company's share of the earnings or losses from investment funds is generally reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements. Financial services investment funds include the Company’s minority investment in Lifson Re, a Bermuda reinsurance company. Effective January 1, 2021, Lifson Re participates on a fully collateralized basis in a majority of the Company’s reinsurance placements for a 22.5% share of placed amounts. This pertains to all traditional reinsurance/retrocessional placements for both property and casualty business where there is more than one open market reinsurer participating. As of March 31, 2021, the Company has ceded approximately $53 million of written premiums to Lifson Re.

Real Estate

Real Estate	3 Months Ended
	Mar. 31, 2021
Real Estate [Abstract]
Real Estate	Real Estate Investment in real estate represents directly owned property held for investment, as follows: Carrying Value March 31, December 31, (In thousands) 2021 2020 Properties in operation $ 1,737,394 $ 1,738,144 Properties under development 223,818 222,770 Total $ 1,961,212 $ 1,960,914 As of March 31, 2021, properties in operation included a long-term ground lease in Washington, D.C., an office complex in New York City, office buildings in West Palm Beach and Palm Beach, Florida, an office building in London, U.K., and the completed portion of a mixed-use project in Washington D.C. Properties in operation are net of accumulated depreciation and amortization of $90,424,000 and $86,970,000 as of March 31, 2021 and December 31, 2020, respectively. Related depreciation expense was $4,890,000 and $6,620,000 for the three months ended March 31, 2021 and 2020, respectively. Future minimum rental income expected on operating leases relating to properties in operation is $51,375,848 in 2021, $69,979,774 in 2022, $62,948,942 in 2023, $59,715,831 in 2024, $55,715,947 in 2025, $51,654,944 in 2026 and $594,894,205 thereafter.

Loans Receivable

Loans Receivable	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Loans Receivable	Loans Receivable At March 31, 2021 and December 31, 2020, loans receivable were as follows: (In thousands) March 31, December 31, Amortized cost (net of allowance for expected credit losses): Real estate loans $ 51,717 $ 51,910 Commercial loans 25,179 33,003 Total $ 76,896 $ 84,913 Fair value: Real estate loans $ 53,325 $ 53,593 Commercial loans 25,179 33,003 Total $ 78,504 $ 86,596 The real estate loans are secured by commercial real estate primarily located in New York. These loans generally earn interest at floating LIBOR-based interest rates and have maturities (inclusive of extension options) through August 2025. The commercial loans are with small business owners who have secured the related financing with the assets of the business. Commercial loans primarily earn interest on a fixed basis and have varying maturities generally not exceeding 10 years. Loans receivable in non-accrual status were both $0.2 million as of March 31, 2021 and December 31, 2020. The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2021: Real Estate Loans Commercial Loans Total (In thousands) Allowance for expected credit losses at December 31, 2020 $ 1,683 $ 3,754 $ 5,437 Provision for expected credit losses (75) (1,164) (1,239) Allowance for expected credit losses at March 31, 2021 $ 1,608 $ 2,590 $ 4,198 The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2020: Real Estate Loans Commercial Loans Total (In thousands) Allowance for expected credit losses at January 1, 2020 $ 1,502 $ 644 $ 2,146 Cumulative effect adjustment resulting from changes in accounting principles (905) 548 (357) Provision for expected credit losses 838 1,301 2,139 Allowance for expected credit losses at March 31, 2020 $ 1,435 $ 2,493 $ 3,928 The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions.

Net Investment Gains (Losses)

Net Investment Gains (Losses)	3 Months Ended
	Mar. 31, 2021
Realized and Unrealized Investment Gains (Losses) [Abstract]
Net Investment Gains (Losses)	Net Investment Gains (Losses) Net investment gains (losses) were as follows: For the Three Months (In thousands) 2021 2020 Net investment gains (losses): Fixed maturity securities: Gains $ 8,240 $ 4,931 Losses (2,071) (4,847) Equity securities (1): Net realized gains on investment sales 8,572 — Change in unrealized losses (24,335) (154,467) Investment funds 47,671 30,183 Real estate 12,909 (687) Other 773 (18,398) Net realized and unrealized gains (losses) on investments in earnings before allowance for expected credit losses 51,759 (143,285) Change in allowance for expected credit losses on investments: Fixed maturity securities (18,159) (31,750) Loans receivable 1,239 (2,139) Change in allowance for expected credit losses on investments (16,920) (33,889) Net investment gains (losses) 34,839 (177,174) Income tax (expense) benefit (5,887) 37,207 After-tax net investment gains (losses) $ 28,952 $ (139,967) Change in unrealized investment losses on available for sale securities: Fixed maturity securities without allowance for expected credit losses $ (122,568) $ (326,416) Fixed maturity securities with allowance for expected credit losses 10,355 1,541 Investment funds (1,020) (7,646) Other (502) (329) Total change in unrealized investment losses (113,735) (332,850) Income tax benefit 23,605 73,869 Noncontrolling interests — 1 After-tax change in unrealized investment losses of available for sale securities $ (90,130) $ (258,980) ______________________ (1) The net realized gains or losses on investment sales represent the total gains or losses from the purchase dates of the equity securities. The change in unrealized losses consists of two components: (i) the reversal of the gain or loss recognized in previous periods on equity securities sold and (ii) the change in unrealized gain or loss resulting from mark-to-market adjustments on equity securities still held.

Fixed Maturity Securities In An

Fixed Maturity Securities In An Unrealized Loss Position	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Fixed Maturity Securities In An Unrealized Loss Position	Fixed Maturity Securities in an Unrealized Loss Position The following tables summarize all fixed maturity securities in an unrealized loss position at March 31, 2021 and December 31, 2020 by the length of time those securities have been continuously in an unrealized loss position: Less Than 12 Months 12 Months or Greater Total (In thousands) Fair Gross Fair Gross Fair Gross March 31, 2021 U.S. government and government agency $ 57,625 $ 913 $ 462 $ 2 $ 58,087 $ 915 State and municipal 288,083 4,949 20,219 1,232 308,302 6,181 Mortgage-backed securities 322,410 11,927 30,537 374 352,947 12,301 Asset-backed securities 1,803,588 4,917 652,450 13,243 2,456,038 18,160 Corporate 1,414,453 15,904 113,498 3,214 1,527,951 19,118 Foreign government 309,304 9,253 20,374 33,166 329,678 42,419 Fixed maturity securities $ 4,195,463 $ 47,863 $ 837,540 $ 51,231 $ 5,033,003 $ 99,094 December 31, 2020 U.S. government and government agency $ 47,649 $ 347 $ 17 $ — $ 47,666 $ 347 State and municipal 147,754 1,165 20,528 904 168,282 2,069 Mortgage-backed securities 212,388 5,121 23,943 230 236,331 5,351 Asset-backed securities 1,389,133 6,563 656,877 26,934 2,046,010 33,497 Corporate 612,177 6,721 39,985 1,759 652,162 8,480 Foreign government 143,729 22,871 6,218 21,577 149,947 44,448 Fixed maturity securities $ 2,552,830 $ 42,788 $ 747,568 $ 51,404 $ 3,300,398 $ 94,192 Substantially all of the securities in an unrealized loss position are rated investment grade, except for the securities in the foreign government classification. A significant amount of the unrealized loss on foreign government securities is the result of changes in currency exchange rates. A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2021 is presented in the table below: ($ in thousands) Number of Aggregate Gross Foreign government 19 $ 79,761 $ 39,694 Corporate 8 25,066 2,071 Mortgage-backed securities 5 540 24 Total 32 $ 105,367 $ 41,789 For fixed maturity securities that management does not intend to sell or to be required to sell, the portion of the decline in value that is considered to be due to credit factors is recognized in earnings, and the portion of the decline in value that is considered to be due to non-credit factors is recognized in other comprehensive income.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company’s fixed maturity available for sale securities, equity securities and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows: Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 - Quoted prices for similar assets or valuations based on inputs that are observable. Level 3 - Estimates of fair value based on internal pricing methodologies using unobservable inputs. Unobservable inputs are only used to measure fair value to the extent that observable inputs are not available. Substantially all of the Company’s fixed maturity securities were priced by independent pricing services. The prices provided by the independent pricing services are estimated based on observable market data in active markets utilizing pricing models and processes, which may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, sector groupings, matrix pricing and reference data. The pricing services may prioritize inputs differently on any given day for any security based on market conditions, and not all inputs are available for each security evaluation on any given day. The pricing services used by the Company have indicated that they will only produce an estimate of fair value if objectively verifiable information is available. The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness and periodically performs independent price tests of a sample of securities to ensure proper valuation. If prices from independent pricing services are not available for fixed maturity securities, the Company estimates the fair value. For Level 2 securities, the Company utilizes pricing models and processes which may include benchmark yields, sector groupings, matrix pricing, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, bids, offers and reference data. Where broker quotes are used, the Company generally requests two or more quotes and sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes received from brokers. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information. For Level 3 securities, the Company generally uses a discounted cash flow model to estimate the fair value of fixed maturity securities. The cash flow models are based upon assumptions as to prevailing credit spreads, interest rate and interest rate volatility, time to maturity and subordination levels. Projected cash flows are discounted at rates that are adjusted to reflect illiquidity, where appropriate. The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020 by level: (In thousands) Total Level 1 Level 2 Level 3 March 31, 2021 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 555,714 $ — $ 555,714 $ — State and municipal 3,502,593 — 3,502,593 — Mortgage-backed securities 1,076,024 — 1,076,024 — Asset-backed securities 3,944,638 — 3,944,638 — Corporate 5,218,189 — 5,218,189 — Foreign government 1,029,879 — 1,029,879 — Total fixed maturity securities available for sale 15,327,037 — 15,327,037 — Equity securities: Common stocks 392,163 382,822 — 9,341 Preferred stocks 229,466 — 220,135 9,331 Total equity securities 621,629 382,822 220,135 18,672 Arbitrage trading account 614,721 498,401 116,320 — Total $ 16,563,387 $ 881,223 $ 15,663,492 $ 18,672 Liabilities: Trading account securities sold but not yet purchased $ 218 $ 218 $ — $ — December 31, 2020 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 603,871 $ — $ 603,871 $ — State and municipal 3,620,664 — 3,620,664 — Mortgage-backed securities 1,020,330 — 1,020,330 — Asset-backed securities 3,194,586 — 3,194,586 — Corporate 4,671,581 — 4,670,581 1,000 Foreign government 975,563 — 975,563 — Total fixed maturity securities available for sale 14,086,595 — 14,085,595 1,000 Equity securities: Common stocks 350,181 340,966 — 9,215 Preferred stocks 275,486 — 266,155 9,331 Total equity securities 625,667 340,966 266,155 18,546 Arbitrage trading account 341,473 298,359 43,114 — Total $ 15,053,735 $ 639,325 $ 14,394,864 $ 19,546 Liabilities: Trading account securities sold but not yet purchased $ 10,048 $ 10,048 $ — $ — The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2021 and for the year ended December 31, 2020: Gains (Losses) Included in: (In thousands) Beginning Earnings (Losses) Other Impairments Purchases (Sales) Paydowns / Maturities Transfers In / (Out) Ending Three Months Ended March 31, 2021 Assets: Fixed maturities securities available for sale: Corporate $ 1,000 $ — $ — $ — $ — $ (1,000) $ — $ — $ — Total 1,000 — — — — (1,000) — — — Equity securities: Common stocks $ 9,215 $ 126 $ — $ — $ — $ — $ — $ — $ 9,341 Preferred stocks 9,331 — — — — — — — 9,331 Total 18,546 126 — — — — — — 18,672 Arbitrage trading account — 1 — — — (1) — — — Total $ 19,546 $ 127 $ — $ — $ — $ (1,001) $ — $ — $ 18,672 Year Ended Assets: Fixed maturities securities available for sale: Corporate $ — $ — $ — $ — $ — $ — $ — $ 1,000 $ 1,000 Total — — — — — — — 1,000 1,000 Equity securities: Common stocks 9,053 1,228 — — — (1,066) — — 9,215 Preferred stocks 6,505 (174) — — 3,000 — — — 9,331 Total 15,558 1,054 — — 3,000 (1,066) — — 18,546 Arbitrage trading account — 19 — — — (19) — — — Total $ 15,558 $ 1,073 $ — $ — $ 3,000 $ (1,085) $ — $ 1,000 $ 19,546 For the three months ended March 31, 2021, there were no securities transferred into or out of Level 3. For the year ended December 31, 2020, a fixed maturity security was transferred from Level 2 into Level 3 as a result of observable valuation inputs no longer being available. The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments: March 31, 2021 December 31, 2020 (In thousands) Carrying Value Fair Value Carrying Value Fair Value Assets: Fixed maturity securities $ 15,400,118 $ 15,412,192 $ 14,159,369 $ 14,173,629 Equity securities 621,629 621,629 625,667 625,667 Arbitrage trading account 614,721 614,721 341,473 341,473 Loans receivable 76,896 78,504 84,913 86,596 Cash and cash equivalents 2,014,911 2,014,911 2,372,366 2,372,366 Trading account receivables from brokers and clearing organizations 257,756 257,756 524,727 524,727 Due from broker — — 2,585 2,585 Liabilities: Due to broker 149,295 149,295 — — Trading account securities sold but not yet purchased 218 218 10,048 10,048 Senior notes and other debt 2,021,142 2,191,022 1,623,025 1,892,444 Subordinated debentures 1,289,272 1,364,002 1,102,309 1,202,842 The estimated fair values of the Company’s fixed maturity securities, equity securities and arbitrage trading account securities are based on various valuation techniques that rely on fair value measurements as described in Note 15. The fair value of loans receivable are estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes and other debt and the subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.

Reserves for Loss and Loss Expe

Reserves for Loss and Loss Expenses	3 Months Ended
	Mar. 31, 2021
Insurance [Abstract]
Reserves for Loss and Loss Expenses	Reserves for Loss and Loss Expenses The Company's reserves for losses and loss expenses are comprised of case reserves and incurred but not reported liabilities ("IBNR"). When a claim is reported, a case reserve is established for the estimated ultimate payment based upon known information about the claim. As more information about the claim becomes available over time, case reserves are adjusted up or down as appropriate. Reserves are also established on an aggregate basis to provide for IBNR liabilities and expected loss reserve development on reported claims. Loss reserves included in the Company’s financial statements represent management’s best estimates based upon an actuarially derived point estimate and other considerations. The Company uses a variety of actuarial techniques and methods to derive an actuarial point estimate for each operating unit. These methods include paid loss development, incurred loss development, paid and incurred Bornhuetter-Ferguson methods and frequency and severity methods. In circumstances where one actuarial method is considered more credible than the others, that method is used to set the point estimate. The actuarial point estimate may also be based on a judgmental weighting of estimates produced from each of the methods considered. Industry loss experience is used to supplement the Company’s own data in selecting “tail factors” in areas where the Company’s own data is limited. The actuarial data is analyzed by line of business, coverage and accident or policy year, as appropriate, for each operating unit. The establishment of the actuarially derived loss reserve point estimate also includes consideration of qualitative factors that may affect the ultimate losses. These qualitative considerations include, among others, the impact of re-underwriting initiatives, changes in the mix of business, changes in distribution sources and changes in policy terms and conditions. The key assumptions used to arrive at the best estimate of loss reserves are the expected loss ratios, rate of loss cost inflation, and reported and paid loss emergence patterns. Expected loss ratios represent management’s expectation of losses at the time the business is priced and written, before any actual claims experience has emerged. This expectation is a significant determinant of the estimate of loss reserves for recently written business where there is little paid or incurred loss data to consider. Expected loss ratios are generally derived from historical loss ratios adjusted for the impact of rate changes, loss cost trends and known changes in the type of risks underwritten. Expected loss ratios are estimated for each key line of business within each operating unit. Expected loss cost inflation is particularly important for the long-tail lines, such as excess casualty, and claims with a high medical component, such as workers’ compensation. Reported and paid loss emergence patterns are used to project current reported or paid loss amounts to their ultimate settlement value. Loss development factors are based on the historical emergence patterns of paid and incurred losses, and are derived from the Company’s own experience and industry data. The paid loss emergence pattern is also significant to excess and assumed workers’ compensation reserves because those reserves are discounted to their estimated present value based upon such estimated payout patterns. Loss frequency and severity are measures of loss activity that are considered in determining the key assumptions described in our discussion of loss and loss expense reserves, including expected loss ratios, rate of loss cost inflation and reported and paid loss emergence patterns. Loss frequency is a measure of the number of claims per unit of insured exposure, and loss severity is a measure of the average size of claims. Factors affecting loss frequency include the effectiveness of loss controls and safety programs and changes in economic activity or weather patterns. Factors affecting loss severity include changes in policy limits, retentions, rate of inflation and judicial interpretations. Another factor affecting estimates of loss frequency and severity is the loss reporting lag, which is the period of time between the occurrence of a loss and the date the loss is reported to the Company. The length of the loss reporting lag affects our ability to accurately predict loss frequency (loss frequencies are more predictable for lines with short reporting lags) as well as the amount of reserves needed for incurred but not reported losses (less IBNR is required for lines with short reporting lags). As a result, loss reserves for lines with short reporting lags are likely to have less variation from initial loss estimates. For lines with short reporting lags, which include commercial automobile, primary workers’ compensation, other liability (claims-made) and property business, the key assumption is the loss emergence pattern used to project ultimate loss estimates from known losses paid or reported to date. For lines of business with long reporting lags, which include other liability (occurrence), products liability, excess workers’ compensation and liability reinsurance, the key assumption is the expected loss ratio since there is often little paid or incurred loss data to consider. Historically, the Company has experienced less variation from its initial loss estimates for lines of businesses with short reporting lags than for lines of business with long reporting lags. The key assumptions used in calculating the most recent estimate of the loss reserves are reviewed each quarter and adjusted, to the extent necessary, to reflect the latest reported loss data, current trends and other factors observed. The table below provides a reconciliation of the beginning and ending reserve balances: March 31, (In thousands) 2021 2020 Net reserves at beginning of period $ 11,620,393 $ 10,697,998 Cumulative effect adjustment resulting from changes in accounting principles — 5,927 Restated net reserves at beginning of period 11,620,393 10,703,925 Net provision for losses and loss expenses: Claims occurring during the current year (1) 1,115,173 1,097,523 (Decrease) increase in estimates for claims occurring in prior years (2) (3) (859) 433 Loss reserve discount accretion 7,278 9,297 Total 1,121,592 1,107,253 Net payments for claims: Current year 97,586 84,310 Prior years 794,472 864,064 Total 892,058 948,374 Foreign currency translation (14,779) (77,167) Net reserves at end of period 11,835,148 10,785,637 Ceded reserves at end of period 2,245,380 1,946,878 Gross reserves at end of period $ 14,080,528 $ 12,732,515 _______________________________________ (1) Claims occurring during the current year are net of loss reserve discounts of $5 million and $3 million for the three months ended March 31, 2021 and 2020, respectively. (2) The change in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $5 million and $4 million for the three months ended March 31, 2021 and 2020, respectively. (3) For certain retrospectively rated insurance policies and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable development, net of additional and return premiums, was $3 million and $4 million for the three months ended March 31, 2021 and 2020, respectively. The ongoing COVID-19 global pandemic has impacted, and will likely continue to impact, the Company’s results through its effect on claim frequency and severity. Loss cost trends have been impacted and will likely be further impacted by COVID-19-related claims in certain lines of business, as well as by other effects of COVID-19 associated with economic conditions, inflation, and social distancing and work from home rules, for example. It remains too early to determine the ultimate net impact of COVID-19. Losses incurred from COVID-19-related claims as well as increased severity are being offset, to a certain extent, by lower claim frequency in certain lines of our businesses, including commercial auto, workers’ compensation, and other liability. However, as the economy and legal systems continue to reopen, we expect the benefit of lower claim frequency in certain lines of business will abate. Given the continuing nature of the pandemic, the direct and indirect impacts of COVID-19 remain uncertain and ultimately could increase or decrease overall loss cost trends and will likely continue to have differing impacts on the Company's different lines of business. Most of the COVID-19-related claims reported to the Company to date involve certain short-tailed lines of business, including contingency and event cancellation, business interruption, and film production delay. Until the economy fully reopens, the Company expects additional claims to be reported for these lines of business. The Company has also received COVID-19-related claims for longer-tailed casualty lines of business such as workers’ compensation and other liability; however, the estimated incurred loss impact for these reported claims appears to be modest at this time. Given the continuing uncertainty regarding the pandemic's pervasiveness, the future impact that the pandemic may have on claim frequency and severity remains uncertain at this time. In workers’ compensation, for example, currently nearly one-half of the states still have rules, legislation or administrative orders creating a presumption that certain “essential” workers who contract COVID-19 did so through the course of their employment. Several other states are considering similar actions, including varying the definition of “essential” workers. While the ultimate impact of these presumptions remains unknown at this time, the Company believes that such state actions will likely increase workers’ compensation claims with respect to workers deemed “essential,” although this impact may be partially offset by lower workers’ compensation claim frequency with respect to non-essential workers. The Company has estimated the potential COVID-19 impact to its contingency and event cancellation, workers’ compensation, and other lines of business under a number of possible scenarios; however, due to COVID-19’s continued evolving impact and the still limited amount of available data, there remains a high degree of uncertainty around the Company’s COVID-19 reserves. In addition, several states (and international jurisdictions), through regulation, legislation and/or judicial action, continue to seek to expand policy coverage terms beyond the policy’s intended coverage, including, for example, but not limited to, property coverages, where there are attempts to extend business interruption coverage where there is no physical damage or loss to property, and attempts to disregard policy exclusions for communicable disease. Accordingly, losses arising from these actions, and the other factors described above, could exceed the Company’s reserves established for those related policies. As of March 31, 2021, the Company had recognized losses for COVID-19-related claims activity, net of reinsurance, of approximately $204 million, of which $183 million relates to the Insurance segment and $21 million relates to the Reinsurance & Monoline Excess segment. Such $204 million of COVID-19-related losses included $120 million of reported losses and $84 million of IBNR. For the three months ended March 31, 2021, the Company recognized current accident year losses for COVID-19-related claims activity, net of reinsurance, of approximately $15 million, all of which relates to the Insurance segment. During the three months ended March 31, 2021, favorable prior year development (net of additional and return premiums) of $3 million included $6 million of favorable development for the Insurance segment, partially offset by $3 million of adverse development for the Reinsurance & Monoline Excess segment. The overall favorable development for the Insurance segment was primarily attributable to favorable development on the 2020 accident year, partially offset by adverse development on the 2016 through 2018 accident years. The favorable development on the 2020 accident year was largely concentrated in the commercial auto liability and other liability lines of business. During 2020, the Company achieved larger rate increases in these lines of business than were contemplated in its budget and initial loss ratio selections. The Company also experienced significantly lower reported claim frequency in these lines in 2020 relative to historical averages, and lower reported incurred losses relative to our expectations. We believe that the lower claim frequency and lower reported incurred losses were caused by the impacts of the COVID-19 pandemic, including for example, lockdowns, reduced driving and traffic, work from home, court closures, etc.; however, due to the ongoing uncertainty regarding the ultimate impacts of the pandemic on accident year 2020 incurred losses, the Company did not adjust its reserves based on these lower trends during 2020. As of March 31, 2021 we began to recognize some of the favorable accident year 2020 experience in certain lines in our ultimate loss picks. The adverse development on the 2016 through 2018 accident years is concentrated in the other liability line of business, and is driven by a higher than expected number of large losses reported. The large losses particularly impacted directors and officers liability and excess and surplus lines casualty classes of business. Prior year reserve development for the Reinsurance & Monoline Excess segment was less significant during the first quarter of 2021, and consisted of small adverse or favorable movements across many lines of business, which largely offset each other. The largest contributor to the slight overall adverse development for the segment was non-proportional reinsurance assumed property business, which was impacted by higher than expected reported losses on property per risk treaties written in the U.S. and U.K. related to accident year 2020. During the three months ended March 31, 2020, favorable prior year development (net of additional and return premiums) of $4 million included $7 million of favorable development for the Insurance segment, partially offset by $3 million of adverse development for the Reinsurance & Monoline Excess segment. The overall favorable development for the Insurance segment was primarily attributable to favorable development on workers’ compensation business, partially offset by adverse development on professional liability business. The favorable workers’ compensation development was spread across many accident years, including prior to 2010, and was especially significant in accident years 2018 and 2019. The favorable workers’ compensation development reflects a continuation of the benign loss cost trends experienced during recent years, particularly the favorable claim frequency trends (i.e., number of reported claims per unit of exposure). In addition, ongoing workers’ compensation claims management efforts, including active medical case management and use of networks and specialty vendors to control medical and pharmaceutical benefit costs, have added to the Company’s favorable workers’ compensation prior year development. The adverse professional liability development was mainly concentrated in accident years 2016 and 2017, but was also spread to a lesser degree across other accident years. The development mainly relates to directors and officers and lawyers professional liability lines of business, and was driven by a higher than expected number of large losses being reported in the period. The Company also experienced a small amount of adverse prior year development during the first quarter 2020 on general liability business stemming from large losses in its excess and surplus lines book of business, mainly in accident years 2016 and 2017. The adverse development for the Reinsurance & Monoline Excess segment was mainly driven by non-proportional reinsurance assumed liability business written in the U.K., primarily from accident years 2015 through 2019. The development was driven by a higher than expected number of reported large losses.

Fair Value Of Financial Instrum

Fair Value Of Financial Instruments	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	Fair Value Measurements The Company’s fixed maturity available for sale securities, equity securities and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows: Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 - Quoted prices for similar assets or valuations based on inputs that are observable. Level 3 - Estimates of fair value based on internal pricing methodologies using unobservable inputs. Unobservable inputs are only used to measure fair value to the extent that observable inputs are not available. Substantially all of the Company’s fixed maturity securities were priced by independent pricing services. The prices provided by the independent pricing services are estimated based on observable market data in active markets utilizing pricing models and processes, which may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, sector groupings, matrix pricing and reference data. The pricing services may prioritize inputs differently on any given day for any security based on market conditions, and not all inputs are available for each security evaluation on any given day. The pricing services used by the Company have indicated that they will only produce an estimate of fair value if objectively verifiable information is available. The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness and periodically performs independent price tests of a sample of securities to ensure proper valuation. If prices from independent pricing services are not available for fixed maturity securities, the Company estimates the fair value. For Level 2 securities, the Company utilizes pricing models and processes which may include benchmark yields, sector groupings, matrix pricing, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, bids, offers and reference data. Where broker quotes are used, the Company generally requests two or more quotes and sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes received from brokers. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information. For Level 3 securities, the Company generally uses a discounted cash flow model to estimate the fair value of fixed maturity securities. The cash flow models are based upon assumptions as to prevailing credit spreads, interest rate and interest rate volatility, time to maturity and subordination levels. Projected cash flows are discounted at rates that are adjusted to reflect illiquidity, where appropriate. The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020 by level: (In thousands) Total Level 1 Level 2 Level 3 March 31, 2021 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 555,714 $ — $ 555,714 $ — State and municipal 3,502,593 — 3,502,593 — Mortgage-backed securities 1,076,024 — 1,076,024 — Asset-backed securities 3,944,638 — 3,944,638 — Corporate 5,218,189 — 5,218,189 — Foreign government 1,029,879 — 1,029,879 — Total fixed maturity securities available for sale 15,327,037 — 15,327,037 — Equity securities: Common stocks 392,163 382,822 — 9,341 Preferred stocks 229,466 — 220,135 9,331 Total equity securities 621,629 382,822 220,135 18,672 Arbitrage trading account 614,721 498,401 116,320 — Total $ 16,563,387 $ 881,223 $ 15,663,492 $ 18,672 Liabilities: Trading account securities sold but not yet purchased $ 218 $ 218 $ — $ — December 31, 2020 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 603,871 $ — $ 603,871 $ — State and municipal 3,620,664 — 3,620,664 — Mortgage-backed securities 1,020,330 — 1,020,330 — Asset-backed securities 3,194,586 — 3,194,586 — Corporate 4,671,581 — 4,670,581 1,000 Foreign government 975,563 — 975,563 — Total fixed maturity securities available for sale 14,086,595 — 14,085,595 1,000 Equity securities: Common stocks 350,181 340,966 — 9,215 Preferred stocks 275,486 — 266,155 9,331 Total equity securities 625,667 340,966 266,155 18,546 Arbitrage trading account 341,473 298,359 43,114 — Total $ 15,053,735 $ 639,325 $ 14,394,864 $ 19,546 Liabilities: Trading account securities sold but not yet purchased $ 10,048 $ 10,048 $ — $ — The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2021 and for the year ended December 31, 2020: Gains (Losses) Included in: (In thousands) Beginning Earnings (Losses) Other Impairments Purchases (Sales) Paydowns / Maturities Transfers In / (Out) Ending Three Months Ended March 31, 2021 Assets: Fixed maturities securities available for sale: Corporate $ 1,000 $ — $ — $ — $ — $ (1,000) $ — $ — $ — Total 1,000 — — — — (1,000) — — — Equity securities: Common stocks $ 9,215 $ 126 $ — $ — $ — $ — $ — $ — $ 9,341 Preferred stocks 9,331 — — — — — — — 9,331 Total 18,546 126 — — — — — — 18,672 Arbitrage trading account — 1 — — — (1) — — — Total $ 19,546 $ 127 $ — $ — $ — $ (1,001) $ — $ — $ 18,672 Year Ended Assets: Fixed maturities securities available for sale: Corporate $ — $ — $ — $ — $ — $ — $ — $ 1,000 $ 1,000 Total — — — — — — — 1,000 1,000 Equity securities: Common stocks 9,053 1,228 — — — (1,066) — — 9,215 Preferred stocks 6,505 (174) — — 3,000 — — — 9,331 Total 15,558 1,054 — — 3,000 (1,066) — — 18,546 Arbitrage trading account — 19 — — — (19) — — — Total $ 15,558 $ 1,073 $ — $ — $ 3,000 $ (1,085) $ — $ 1,000 $ 19,546 For the three months ended March 31, 2021, there were no securities transferred into or out of Level 3. For the year ended December 31, 2020, a fixed maturity security was transferred from Level 2 into Level 3 as a result of observable valuation inputs no longer being available. The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments: March 31, 2021 December 31, 2020 (In thousands) Carrying Value Fair Value Carrying Value Fair Value Assets: Fixed maturity securities $ 15,400,118 $ 15,412,192 $ 14,159,369 $ 14,173,629 Equity securities 621,629 621,629 625,667 625,667 Arbitrage trading account 614,721 614,721 341,473 341,473 Loans receivable 76,896 78,504 84,913 86,596 Cash and cash equivalents 2,014,911 2,014,911 2,372,366 2,372,366 Trading account receivables from brokers and clearing organizations 257,756 257,756 524,727 524,727 Due from broker — — 2,585 2,585 Liabilities: Due to broker 149,295 149,295 — — Trading account securities sold but not yet purchased 218 218 10,048 10,048 Senior notes and other debt 2,021,142 2,191,022 1,623,025 1,892,444 Subordinated debentures 1,289,272 1,364,002 1,102,309 1,202,842 The estimated fair values of the Company’s fixed maturity securities, equity securities and arbitrage trading account securities are based on various valuation techniques that rely on fair value measurements as described in Note 15. The fair value of loans receivable are estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes and other debt and the subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.

Premiums and Reinsurance Relate

Premiums and Reinsurance Related Information	3 Months Ended
	Mar. 31, 2021
Insurance [Abstract]
Premiums and Reinsurance Related Information	Premiums and Reinsurance Related Information The following is a summary of insurance and reinsurance financial information: For the Three Months (In thousands) 2021 2020 Written premiums: Direct $ 2,177,162 $ 1,964,490 Assumed 307,550 266,882 Ceded (434,674) (385,526) Total net premiums written $ 2,050,038 $ 1,845,846 Earned premiums: Direct $ 2,003,045 $ 1,829,713 Assumed 259,541 228,214 Ceded (412,630) (366,509) Total net premiums earned $ 1,849,956 $ 1,691,418 Ceded losses and loss expenses incurred $ 298,740 $ 235,183 Ceded commissions earned $ 101,680 $ 81,045 The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2021: (In thousands) Allowance for expected credit losses at December 31, 2020 $ 22,883 Provision for expected credit losses 1,381 Allowance for expected credit losses at March 31, 2021 $ 24,264 The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2020: (In thousands) Allowance for expected credit losses at January 1, 2020 $ 19,823 Cumulative effect adjustment resulting from changes in accounting principles 1,270 Provision for expected credit losses 431 Allowance for expected credit losses at March 31, 2020 $ 21,524 The Company reinsures a portion of its insurance exposures in order to reduce its net liability on individual risks and catastrophe losses. The Company also cedes premiums to state assigned risk plans and captive insurance companies. Estimated amounts due from reinsurers are reported net of an allowance for expected credit losses. The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2021: (In thousands) Allowance for expected credit losses at December 31, 2020 $ 7,801 Provision for expected credit losses (428) Allowance for expected credit losses at March 31, 2021 $ 7,373 The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2020: (In thousands) Allowance for expected credit losses at January 1, 2020 $ 690 Cumulative effect adjustment resulting from changes in accounting principles 5,927 Provision for expected credit losses 183 Allowance for expected credit losses at March 31, 2020 $ 6,800

Restricted Stock Units

Restricted Stock Units	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Restricted Stock Units	Restricted Stock Units Pursuant to its stock incentive plan, the Company may issue restricted stock units ("RSUs") to employees of the Company and its subsidiaries. The RSUs generally vest three ($ in thousands) Units Fair Value 2021 590 $ 40 2020 724 $ 57

Litigation and Contingent Liabi

Litigation and Contingent Liabilities	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Litigation and Contingent Liabilities	Litigation and Contingent Liabilities    In the ordinary course of business, the Company is subject to disputes, litigation and arbitration arising from its insurance and reinsurance businesses. These matters are generally related to insurance and reinsurance claims and are considered in the establishment of loss and loss expense reserves. In addition, the Company may also become involved in legal actions which seek extra-contractual damages, punitive damages or penalties, including claims alleging bad faith in handling of insurance claims. The Company expects its ultimate liability with respect to such matters will not be material to its financial condition. However, adverse outcomes on such matters are possible, from time to time, and could be material to the Company’s results of operations in any particular financial reporting period.

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Leases Lessees are required to recognize a right-of-use asset and a lease liability for leases with terms of more than 12 months on the balance sheet. All leases disclosed within this footnote are classified as operating leases. Recognized right-of-use asset and lease liability are reported within other assets and other liabilities, respectively, in the consolidated balance sheet. Lease expense is reported in other operating costs and expenses in the consolidated statement of income and accounted for on a straight-line basis over the lease term. To determine the discount rate used to calculate present value of future minimum lease payments, the Company uses its incremental borrowing rate during the lease commencement period in line with the respective lease duration. In certain cases, the Company has the option to renew the lease. Lease renewal future payments are included in the present value of the future minimum lease payments when the Company determines it is reasonably certain to renew. The main leases entered into by the Company are for office space used by the Company’s operating units across the world. Additionally, the Company, to a lesser extent, has equipment leases mainly for office equipment. Further information relating to operating lease expense and other operating lease information are as follows: For the Three Months Ended (In thousands) 2021 2020 Leases: Lease cost $ 11,264 $ 11,236 Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows $ 11,377 $ 10,830 Right-of-use assets obtained in exchange for new lease liabilities $ 30 $ 1,612 As of March 31 ($ in thousands) 2021 2020 Right-of-use assets $ 156,942 $ 184,544 Lease liabilities $ 195,590 $ 224,189 Weighted-average remaining lease term 6.73 years 6.95 years Weighted-average discount rate 5.94 % 5.95 % Contractual maturities of the Company’s future minimum lease payments are as follows: (In thousands) March 31, 2021 Contractual Maturities: 2021 $ 35,596 2022 41,887 2023 38,218 2024 31,694 2025 22,881 Thereafter 56,217 Total undiscounted future minimum lease payments 226,493 Less: Discount impact (30,903) Total lease liability $ 195,590

Business Segments

Business Segments	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Business Segments	Business Segments The Company’s reportable segments include the following two business segments, plus a corporate segment: • Insurance - predominantly commercial insurance business, including excess and surplus lines, admitted lines and specialty personal lines throughout the United States, as well as insurance business in the United Kingdom, Continental Europe, South America, Canada, Mexico, Scandinavia, Asia and Australia. • Reinsurance & Monoline Excess - reinsurance business on a facultative and treaty basis, primarily in the United States, the United Kingdom, Continental Europe, Australia, the Asia-Pacific Region and South Africa, as well as operations that solely retain risk on an excess basis. The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Income tax expense and benefits are calculated based upon the Company's overall effective tax rate. Summary financial information about the Company's reporting segments is presented in the following tables. Income (loss) before income taxes by segment includes allocated investment income. Identifiable assets by segment are those assets used in or allocated to the operation of each segment. Revenues (In thousands) Earned Investment Other Total (2) Pre-Tax Income (Loss) Net Income (Loss) to Common Stockholders Three months ended March 31, 2021 Insurance $ 1,604,979 $ 105,237 $ 8,279 $ 1,718,495 $ 257,109 $ 198,708 Reinsurance & Monoline Excess 244,977 37,708 — 282,685 68,649 54,471 Corporate, other and eliminations (3) — 15,632 105,218 120,850 (64,529) (52,606) Net investment gains — — 34,839 34,839 34,839 28,952 Total $ 1,849,956 $ 158,577 $ 148,336 $ 2,156,869 $ 296,068 $ 229,525 Three months ended March 31, 2020 Insurance $ 1,484,955 $ 123,458 $ 8,473 $ 1,616,886 $ 175,947 $ 140,117 Reinsurance & Monoline Excess 206,463 37,710 — 244,173 36,514 29,187 Corporate, other and eliminations (3) — 13,595 113,130 126,725 (41,755) (33,755) Net investment losses — — (177,174) (177,174) (177,174) (139,967) Total $ 1,691,418 $ 174,763 $ (55,571) $ 1,810,610 $ (6,468) $ (4,418) _________________ (1) Certain amounts included in earned premiums of each segment are related to inter-segment transactions. (2) Revenues for Insurance from foreign countries for the three months ended March 31, 2021 and 2020 were $196 million and $168 million, respectively. Revenues for Reinsurance & Monoline Excess from foreign countries for the three months ended March 31, 2021 and 2020 were $88 million and $69 million, respectively. (3) Corporate, other and eliminations represent corporate revenues and expenses that are not allocated to business segments. Identifiable Assets (In thousands) March 31, December 31, Insurance $ 21,985,027 $ 21,702,328 Reinsurance & Monoline Excess 4,678,740 4,654,158 Corporate, other and eliminations 3,127,507 2,215,479 Consolidated $ 29,791,274 $ 28,571,965 Net premiums earned by major line of business are as follows: For the Three Months (In thousands) 2021 2020 Insurance: Other liability $ 601,902 $ 547,129 Short-tail lines (1) 324,740 295,478 Workers' compensation 267,449 301,600 Commercial automobile 220,761 189,643 Professional liability 190,128 151,105 Total Insurance 1,604,979 1,484,955 Reinsurance & Monoline Excess: Casualty reinsurance 149,638 122,731 Property reinsurance 49,466 41,571 Monoline excess (2) 45,873 42,161 Total Reinsurance & Monoline Excess 244,977 206,463 Total $ 1,849,956 $ 1,691,418 ______________ (1) Short-tail lines include commercial multi-peril (non-liability), inland marine, accident and health, fidelity and surety, boiler and machinery and other lines.

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements and Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Per Share Data	Per Share Data The Company presents both basic and diluted net income (loss) per share (“EPS”) amounts. Basic EPS is calculated by dividing net income (loss) by the weighted average number of common shares outstanding during the period (including 7,767,874 and 7,575,168 common shares held in a grantor trust as of March 31, 2021 and 2020, respectively). The common shares held in the grantor trust are for delivery upon settlement of vested but mandatorily deferred restricted stock units ("RSUs"). Shares held by the grantor trust do not affect diluted shares outstanding since the shares deliverable under vested RSUs were already included in diluted shares outstanding. Diluted EPS is based upon the weighted average number of basic and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. For the period ended March 31, 2020, diluted shares have been reduced by 2.0 million to reflect the anti-dilutive effect of common equivalent shares. The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows: For the Three Months (In thousands) 2021 2020 Basic 185,195 190,287 Diluted 186,830 190,287
Recent Accounting Pronouncements	Recent Accounting Pronouncements and Accounting Policies Recently adopted accounting pronouncements: All accounting and reporting standards that have become effective in 2021 were either not applicable to the Company or their adoption did not have a material impact on the Company. Accounting and reporting standards that are not yet effective: All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

Per Share Data (Tables)

Per Share Data (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Weighted average number of common shares	The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows: For the Three Months (In thousands) 2021 2020 Basic 185,195 190,287 Diluted 186,830 190,287

Consolidated Statements of Co_3

Consolidated Statements of Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Components of changes in accumulated other comprehensive income (loss)	The following table presents the components of the changes in accumulated other comprehensive income (loss) ("AOCI"): (In thousands) Unrealized Investment Gains (Losses) Currency Translation Adjustments Accumulated Other Comprehensive As of and for the three months ended March 31, 2021 Changes in AOCI Beginning of period $ 289,714 $ (351,886) $ (62,172) Other comprehensive (loss) income before reclassifications (98,991) 4,050 (94,941) Amounts reclassified from AOCI 8,861 — 8,861 Other comprehensive (loss) income (90,130) 4,050 (86,080) Unrealized investment gain related to noncontrolling interest — — — End of period $ 199,584 $ (347,836) $ (148,252) Amounts reclassified from AOCI Pre-tax $ 11,216 (1) $ — $ 11,216 Tax effect (2,355) (2) — (2,355) After-tax amounts reclassified $ 8,861 $ — $ 8,861 Other comprehensive (loss) income Pre-tax $ (113,735) $ 4,050 $ (109,685) Tax effect 23,605 — 23,605 Other comprehensive (loss) income $ (90,130) $ 4,050 $ (86,080) As of and for the three months ended March 31, 2020 Changes in AOCI Beginning of period $ 124,514 $ (381,813) $ (257,299) Cumulative effect adjustment resulting from changes in accounting principles 24,952 — 24,952 Restated beginning of period 149,466 (381,813) (232,347) Other comprehensive loss before reclassifications (298,531) (98,194) (396,725) Amounts reclassified from AOCI 39,550 — 39,550 Other comprehensive loss (258,981) (98,194) (357,175) Unrealized investment loss related to noncontrolling interest 1 — 1 End of period $ (109,514) $ (480,007) $ (589,521) Amounts reclassified from AOCI Pre-tax $ 50,063 (1) $ — $ 50,063 Tax effect (10,513) (2) — (10,513) After-tax amounts reclassified $ 39,550 $ — $ 39,550 Other comprehensive loss Pre-tax $ (332,850) $ (98,194) $ (431,044) Tax effect 73,869 — 73,869 Other comprehensive loss $ (258,981) $ (98,194) $ (357,175) ____________ (1) Net investment gains (losses) in the consolidated statements of income (loss). (2) Income tax (expense) benefit in the consolidated statements of income (loss).

Investments in Fixed Maturity_2

Investments in Fixed Maturity Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Schedule of investments in fixed maturity securities	At March 31, 2021 and December 31, 2020, investments in fixed maturity securities were as follows: (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses March 31, 2021 Held to maturity: State and municipal $ 67,710 $ (730) $ 11,150 $ — $ 78,130 $ 66,980 Residential mortgage-backed 6,101 — 924 — 7,025 6,101 Total held to maturity 73,811 (730) 12,074 — 85,155 73,081 Available for sale: U.S. government and government agency 541,180 — 15,449 (915) 555,714 555,714 State and municipal: Special revenue 2,112,542 — 78,450 (3,284) 2,187,708 2,187,708 State general obligation 399,636 — 28,156 (1,059) 426,733 426,733 Pre-refunded 231,235 — 17,990 (465) 248,760 248,760 Corporate backed 164,542 — 8,585 (788) 172,339 172,339 Local general obligation 432,788 — 34,850 (585) 467,053 467,053 Total state and municipal 3,340,743 — 168,031 (6,181) 3,502,593 3,502,593 Mortgage-backed securities: Residential 889,638 — 19,315 (12,215) 896,738 896,738 Commercial 172,817 — 6,555 (86) 179,286 179,286 Total mortgage-backed securities 1,062,455 — 25,870 (12,301) 1,076,024 1,076,024 Asset-backed 3,952,009 — 10,789 (18,160) 3,944,638 3,944,638 Corporate: Industrial 2,986,688 (16) 88,810 (14,819) 3,060,663 3,060,663 Financial 1,517,251 — 48,756 (1,638) 1,564,369 1,564,369 Utilities 426,213 — 15,476 (2,360) 439,329 439,329 Other 153,700 — 429 (301) 153,828 153,828 Total corporate 5,083,852 (16) 153,471 (19,118) 5,218,189 5,218,189 Foreign government 1,072,930 (19,993) 19,361 (42,419) 1,029,879 1,029,879 Total available for sale 15,053,169 (20,009) 392,971 (99,094) 15,327,037 15,327,037 Total investments in fixed maturity securities $ 15,126,980 $ (20,739) $ 405,045 $ (99,094) $ 15,412,192 $ 15,400,118 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income (loss). Amount excludes unrealized losses relating to non-credit factors. (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses December 31, 2020 Held to maturity: State and municipal $ 67,117 $ (798) $ 13,217 $ — $ 79,536 $ 66,319 Residential mortgage-backed 6,455 — 1,043 — 7,498 6,455 Total held to maturity 73,572 (798) 14,260 — 87,034 72,774 Available for sale: U.S. government and government agency 586,020 — 18,198 (347) 603,871 603,871 State and municipal: Special revenue 2,137,162 — 96,924 (714) 2,233,372 2,233,372 State general obligation 417,397 — 33,407 — 450,804 450,804 Pre-refunded 250,081 — 21,472 (162) 271,391 271,391 Corporate backed 206,356 — 8,755 (638) 214,473 214,473 Local general obligation 410,583 — 40,596 (555) 450,624 450,624 Total state and municipal 3,421,579 — 201,154 (2,069) 3,620,664 3,620,664 Mortgage-backed securities: Residential 813,187 — 24,664 (5,238) 832,613 832,613 Commercial 181,105 — 6,725 (113) 187,717 187,717 Total mortgage-backed securities 994,292 — 31,389 (5,351) 1,020,330 1,020,330 Asset-backed 3,218,048 — 10,035 (33,497) 3,194,586 3,194,586 Corporate: Industrial 2,456,516 (518) 115,926 (7,449) 2,564,475 2,564,475 Financial 1,513,943 — 62,947 (987) 1,575,903 1,575,903 Utilities 389,267 — 31,931 (33) 421,165 421,165 Other 109,353 — 696 (11) 110,038 110,038 Total corporate 4,469,079 (518) 211,500 (8,480) 4,671,581 4,671,581 Foreign government 993,268 (1,264) 28,007 (44,448) 975,563 975,563 Total available for sale 13,682,286 (1,782) 500,283 (94,192) 14,086,595 14,086,595 Total investments in fixed maturity securities $ 13,755,858 $ (2,580) $ 514,543 $ (94,192) $ 14,173,629 $ 14,159,369
Debt Securities, Held-to-maturity, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2021: State and Municipal (In thousands) Allowance for expected credit losses at December 31, 2020 $ 798 Provision for expected credit losses (68) Allowance for expected credit losses at March 31, 2021 $ 730 The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2020: State and Municipal (In thousands) Allowance for expected credit losses at January 1, 2020 $ — Cumulative effect adjustment resulting from changes in accounting principles 69 Provision for expected credit losses 38 Allowance for expected credit losses at March 31, 2020 $ 107
Debt Securities, Available-for-sale, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2021: Foreign Government Corporate Total (In thousands) Allowance for expected credit losses at December 31, 2020 $ 1,264 $ 518 $ 1,782 Expected credit losses on securities for which credit losses were not previously recorded 18,990 16 19,006 Expected credit losses on securities for which credit losses were previously recorded (261) (513) (774) Reduction due to disposals — (5) (5) Allowance for expected credit losses at March 31, 2021 $ 19,993 $ 16 $ 20,009 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2020: Foreign Government Corporate Total (In thousands) Allowance for expected credit losses at January 1, 2020 $ — $ — $ — Cumulative effect adjustment resulting from changes in accounting principles 35,645 — 35,645 Expected credit losses on securities for which credit losses were not previously recorded 12,494 6,436 18,930 Expected credit losses on securities for which credit losses were previously recorded 16,369 — 16,369 Reduction due to disposals (3,588) — (3,588) Allowance for expected credit losses at March 31, 2020 $ 60,920 $ 6,436 $ 67,356
Amortized cost and fair value of fixed maturity securities by contractual maturity	The amortized cost and fair value of fixed maturity securities at March 31, 2021, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations. (In thousands) Amortized Fair Due in one year or less $ 1,778,569 $ 1,765,769 Due after one year through five years 6,419,223 6,576,943 Due after five years through ten years 3,500,751 3,592,140 Due after ten years 2,359,151 2,394,291 Mortgage-backed securities 1,068,556 1,083,049 Total $ 15,126,250 $ 15,412,192 ________________

Investments in Equity Securit_2

Investments in Equity Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Real estate
Debt Securities, Available-for-sale [Line Items]
Schedule of Investments in Equity Securities	At March 31, 2021 and December 31, 2020, investments in equity securities were as follows: (In thousands) Cost Gross Unrealized Fair Carrying Gains Losses March 31, 2021 Common stocks $ 339,742 $ 60,766 $ (8,345) $ 392,163 $ 392,163 Preferred stocks 196,569 33,523 (626) 229,466 229,466 Total $ 536,311 $ 94,289 $ (8,971) $ 621,629 $ 621,629 December 31, 2020 Common stocks $ 335,617 $ 28,742 $ (14,178) $ 350,181 $ 350,181 Preferred stocks 180,397 95,581 (492) 275,486 275,486 Total $ 516,014 $ 124,323 $ (14,670) $ 625,667 $ 625,667

Net Investment Income (Tables)

Net Investment Income (Tables)	3 Months Ended
	Mar. 31, 2021
Net Investment Income [Abstract]
Schedule of Net Investment Income	Net investment income consisted of the following: For the Three Months (In thousands) 2021 2020 Investment income earned on: Fixed maturity securities, including cash and cash equivalents and loans receivable $ 94,677 $ 128,018 Investment funds 38,935 40,577 Arbitrage trading account 19,074 1,138 Equity securities 6,180 1,563 Real estate 1,161 6,096 Gross investment income 160,027 177,392 Investment expense (1,450) (2,629) Net investment income $ 158,577 $ 174,763

Investment Funds (Tables)

Investment Funds (Tables)	3 Months Ended
	Mar. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Investment Funds	Investment funds consisted of the following: Carrying Value as of Income from March 31, December 31, For the Three Months (In thousands) 2021 2020 2021 2020 Financial services $ 477,927 $ 434,437 $ 17,142 $ 15,209 Real Estate 304,461 310,783 4,434 6,790 Energy 143,852 140,935 3,320 4,413 Transportation 193,401 190,125 6,228 2,646 Other funds 239,356 233,150 7,811 11,519 Total $ 1,358,997 $ 1,309,430 $ 38,935 $ 40,577

Real Estate (Tables)

Real Estate (Tables)	3 Months Ended
	Mar. 31, 2021
Real Estate [Abstract]
Schedule of Real Estate Investments	Investment in real estate represents directly owned property held for investment, as follows: Carrying Value March 31, December 31, (In thousands) 2021 2020 Properties in operation $ 1,737,394 $ 1,738,144 Properties under development 223,818 222,770 Total $ 1,961,212 $ 1,960,914

Loans Receivable Loans Receivab

Loans Receivable Loans Receivable (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Schedule of Loans Receivable	At March 31, 2021 and December 31, 2020, loans receivable were as follows: (In thousands) March 31, December 31, Amortized cost (net of allowance for expected credit losses): Real estate loans $ 51,717 $ 51,910 Commercial loans 25,179 33,003 Total $ 76,896 $ 84,913 Fair value: Real estate loans $ 53,325 $ 53,593 Commercial loans 25,179 33,003 Total $ 78,504 $ 86,596
Financing Receivable, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2021: Real Estate Loans Commercial Loans Total (In thousands) Allowance for expected credit losses at December 31, 2020 $ 1,683 $ 3,754 $ 5,437 Provision for expected credit losses (75) (1,164) (1,239) Allowance for expected credit losses at March 31, 2021 $ 1,608 $ 2,590 $ 4,198 The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2020: Real Estate Loans Commercial Loans Total (In thousands) Allowance for expected credit losses at January 1, 2020 $ 1,502 $ 644 $ 2,146 Cumulative effect adjustment resulting from changes in accounting principles (905) 548 (357) Provision for expected credit losses 838 1,301 2,139 Allowance for expected credit losses at March 31, 2020 $ 1,435 $ 2,493 $ 3,928

Net Investment Gains (Losses) (

Net Investment Gains (Losses) (Tables)	3 Months Ended
	Mar. 31, 2021
Realized and Unrealized Investment Gains (Losses) [Abstract]
Realized And Unrealized Investment Gains (Losses)	Net investment gains (losses) were as follows: For the Three Months (In thousands) 2021 2020 Net investment gains (losses): Fixed maturity securities: Gains $ 8,240 $ 4,931 Losses (2,071) (4,847) Equity securities (1): Net realized gains on investment sales 8,572 — Change in unrealized losses (24,335) (154,467) Investment funds 47,671 30,183 Real estate 12,909 (687) Other 773 (18,398) Net realized and unrealized gains (losses) on investments in earnings before allowance for expected credit losses 51,759 (143,285) Change in allowance for expected credit losses on investments: Fixed maturity securities (18,159) (31,750) Loans receivable 1,239 (2,139) Change in allowance for expected credit losses on investments (16,920) (33,889) Net investment gains (losses) 34,839 (177,174) Income tax (expense) benefit (5,887) 37,207 After-tax net investment gains (losses) $ 28,952 $ (139,967) Change in unrealized investment losses on available for sale securities: Fixed maturity securities without allowance for expected credit losses $ (122,568) $ (326,416) Fixed maturity securities with allowance for expected credit losses 10,355 1,541 Investment funds (1,020) (7,646) Other (502) (329) Total change in unrealized investment losses (113,735) (332,850) Income tax benefit 23,605 73,869 Noncontrolling interests — 1 After-tax change in unrealized investment losses of available for sale securities $ (90,130) $ (258,980) ______________________ (1) The net realized gains or losses on investment sales represent the total gains or losses from the purchase dates of the equity securities. The change in unrealized losses consists of two components: (i) the reversal of the gain or loss recognized in previous periods on equity securities sold and (ii) the change in unrealized gain or loss resulting from mark-to-market adjustments on equity securities still held.

Fixed Maturity Securities In _2

Fixed Maturity Securities In An Unrealized Loss Position (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Securities in an unrealized loss position	The following tables summarize all fixed maturity securities in an unrealized loss position at March 31, 2021 and December 31, 2020 by the length of time those securities have been continuously in an unrealized loss position: Less Than 12 Months 12 Months or Greater Total (In thousands) Fair Gross Fair Gross Fair Gross March 31, 2021 U.S. government and government agency $ 57,625 $ 913 $ 462 $ 2 $ 58,087 $ 915 State and municipal 288,083 4,949 20,219 1,232 308,302 6,181 Mortgage-backed securities 322,410 11,927 30,537 374 352,947 12,301 Asset-backed securities 1,803,588 4,917 652,450 13,243 2,456,038 18,160 Corporate 1,414,453 15,904 113,498 3,214 1,527,951 19,118 Foreign government 309,304 9,253 20,374 33,166 329,678 42,419 Fixed maturity securities $ 4,195,463 $ 47,863 $ 837,540 $ 51,231 $ 5,033,003 $ 99,094 December 31, 2020 U.S. government and government agency $ 47,649 $ 347 $ 17 $ — $ 47,666 $ 347 State and municipal 147,754 1,165 20,528 904 168,282 2,069 Mortgage-backed securities 212,388 5,121 23,943 230 236,331 5,351 Asset-backed securities 1,389,133 6,563 656,877 26,934 2,046,010 33,497 Corporate 612,177 6,721 39,985 1,759 652,162 8,480 Foreign government 143,729 22,871 6,218 21,577 149,947 44,448 Fixed maturity securities $ 2,552,830 $ 42,788 $ 747,568 $ 51,404 $ 3,300,398 $ 94,192
Non-Investment Grade Fixed Maturity Securities	A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2021 is presented in the table below: ($ in thousands) Number of Aggregate Gross Foreign government 19 $ 79,761 $ 39,694 Corporate 8 25,066 2,071 Mortgage-backed securities 5 540 24 Total 32 $ 105,367 $ 41,789

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Assets And Liabilities Measured At Fair value, On A Recurring Basis	The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020 by level: (In thousands) Total Level 1 Level 2 Level 3 March 31, 2021 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 555,714 $ — $ 555,714 $ — State and municipal 3,502,593 — 3,502,593 — Mortgage-backed securities 1,076,024 — 1,076,024 — Asset-backed securities 3,944,638 — 3,944,638 — Corporate 5,218,189 — 5,218,189 — Foreign government 1,029,879 — 1,029,879 — Total fixed maturity securities available for sale 15,327,037 — 15,327,037 — Equity securities: Common stocks 392,163 382,822 — 9,341 Preferred stocks 229,466 — 220,135 9,331 Total equity securities 621,629 382,822 220,135 18,672 Arbitrage trading account 614,721 498,401 116,320 — Total $ 16,563,387 $ 881,223 $ 15,663,492 $ 18,672 Liabilities: Trading account securities sold but not yet purchased $ 218 $ 218 $ — $ — December 31, 2020 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 603,871 $ — $ 603,871 $ — State and municipal 3,620,664 — 3,620,664 — Mortgage-backed securities 1,020,330 — 1,020,330 — Asset-backed securities 3,194,586 — 3,194,586 — Corporate 4,671,581 — 4,670,581 1,000 Foreign government 975,563 — 975,563 — Total fixed maturity securities available for sale 14,086,595 — 14,085,595 1,000 Equity securities: Common stocks 350,181 340,966 — 9,215 Preferred stocks 275,486 — 266,155 9,331 Total equity securities 625,667 340,966 266,155 18,546 Arbitrage trading account 341,473 298,359 43,114 — Total $ 15,053,735 $ 639,325 $ 14,394,864 $ 19,546 Liabilities: Trading account securities sold but not yet purchased $ 10,048 $ 10,048 $ — $ —
Summarize Changes In Level 3 Assets	The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2021 and for the year ended December 31, 2020: Gains (Losses) Included in: (In thousands) Beginning Earnings (Losses) Other Impairments Purchases (Sales) Paydowns / Maturities Transfers In / (Out) Ending Three Months Ended March 31, 2021 Assets: Fixed maturities securities available for sale: Corporate $ 1,000 $ — $ — $ — $ — $ (1,000) $ — $ — $ — Total 1,000 — — — — (1,000) — — — Equity securities: Common stocks $ 9,215 $ 126 $ — $ — $ — $ — $ — $ — $ 9,341 Preferred stocks 9,331 — — — — — — — 9,331 Total 18,546 126 — — — — — — 18,672 Arbitrage trading account — 1 — — — (1) — — — Total $ 19,546 $ 127 $ — $ — $ — $ (1,001) $ — $ — $ 18,672 Year Ended Assets: Fixed maturities securities available for sale: Corporate $ — $ — $ — $ — $ — $ — $ — $ 1,000 $ 1,000 Total — — — — — — — 1,000 1,000 Equity securities: Common stocks 9,053 1,228 — — — (1,066) — — 9,215 Preferred stocks 6,505 (174) — — 3,000 — — — 9,331 Total 15,558 1,054 — — 3,000 (1,066) — — 18,546 Arbitrage trading account — 19 — — — (19) — — — Total $ 15,558 $ 1,073 $ — $ — $ 3,000 $ (1,085) $ — $ 1,000 $ 19,546

Reserves for Loss and Loss Ex_2

Reserves for Loss and Loss Expenses (Tables)	3 Months Ended
	Mar. 31, 2021
Insurance [Abstract]
Reserve Balances	The table below provides a reconciliation of the beginning and ending reserve balances: March 31, (In thousands) 2021 2020 Net reserves at beginning of period $ 11,620,393 $ 10,697,998 Cumulative effect adjustment resulting from changes in accounting principles — 5,927 Restated net reserves at beginning of period 11,620,393 10,703,925 Net provision for losses and loss expenses: Claims occurring during the current year (1) 1,115,173 1,097,523 (Decrease) increase in estimates for claims occurring in prior years (2) (3) (859) 433 Loss reserve discount accretion 7,278 9,297 Total 1,121,592 1,107,253 Net payments for claims: Current year 97,586 84,310 Prior years 794,472 864,064 Total 892,058 948,374 Foreign currency translation (14,779) (77,167) Net reserves at end of period 11,835,148 10,785,637 Ceded reserves at end of period 2,245,380 1,946,878 Gross reserves at end of period $ 14,080,528 $ 12,732,515 _______________________________________ (1) Claims occurring during the current year are net of loss reserve discounts of $5 million and $3 million for the three months ended March 31, 2021 and 2020, respectively. (2) The change in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $5 million and $4 million for the three months ended March 31, 2021 and 2020, respectively. (3) For certain retrospectively rated insurance policies and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable development, net of additional and return premiums, was $3 million and $4 million for the three months ended March 31, 2021 and 2020, respectively.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Carrying Amounts And Estimated Fair Values Of Financial Instruments	The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments: March 31, 2021 December 31, 2020 (In thousands) Carrying Value Fair Value Carrying Value Fair Value Assets: Fixed maturity securities $ 15,400,118 $ 15,412,192 $ 14,159,369 $ 14,173,629 Equity securities 621,629 621,629 625,667 625,667 Arbitrage trading account 614,721 614,721 341,473 341,473 Loans receivable 76,896 78,504 84,913 86,596 Cash and cash equivalents 2,014,911 2,014,911 2,372,366 2,372,366 Trading account receivables from brokers and clearing organizations 257,756 257,756 524,727 524,727 Due from broker — — 2,585 2,585 Liabilities: Due to broker 149,295 149,295 — — Trading account securities sold but not yet purchased 218 218 10,048 10,048 Senior notes and other debt 2,021,142 2,191,022 1,623,025 1,892,444 Subordinated debentures 1,289,272 1,364,002 1,102,309 1,202,842

Premiums and Reinsurance Rela_2

Premiums and Reinsurance Related Information (Tables)	3 Months Ended
	Mar. 31, 2021
Insurance [Abstract]
Reinsurance Financial Information	The following is a summary of insurance and reinsurance financial information: For the Three Months (In thousands) 2021 2020 Written premiums: Direct $ 2,177,162 $ 1,964,490 Assumed 307,550 266,882 Ceded (434,674) (385,526) Total net premiums written $ 2,050,038 $ 1,845,846 Earned premiums: Direct $ 2,003,045 $ 1,829,713 Assumed 259,541 228,214 Ceded (412,630) (366,509) Total net premiums earned $ 1,849,956 $ 1,691,418 Ceded losses and loss expenses incurred $ 298,740 $ 235,183 Ceded commissions earned $ 101,680 $ 81,045
Premium receivable, allowance for credit loss	The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2021: (In thousands) Allowance for expected credit losses at December 31, 2020 $ 22,883 Provision for expected credit losses 1,381 Allowance for expected credit losses at March 31, 2021 $ 24,264 The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2020: (In thousands) Allowance for expected credit losses at January 1, 2020 $ 19,823 Cumulative effect adjustment resulting from changes in accounting principles 1,270 Provision for expected credit losses 431 Allowance for expected credit losses at March 31, 2020 $ 21,524
Reinsurance Recoverable, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2021: (In thousands) Allowance for expected credit losses at December 31, 2020 $ 7,801 Provision for expected credit losses (428) Allowance for expected credit losses at March 31, 2021 $ 7,373 The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2020: (In thousands) Allowance for expected credit losses at January 1, 2020 $ 690 Cumulative effect adjustment resulting from changes in accounting principles 5,927 Provision for expected credit losses 183 Allowance for expected credit losses at March 31, 2020 $ 6,800

Restricted Stock Units (Tables)

Restricted Stock Units (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary Of Restricted Stock Units Issued	A summary of RSUs issued in the three months ended March 31, 2021 and 2020 follows: ($ in thousands) Units Fair Value 2021 590 $ 40 2020 724 $ 57

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Lease, Cost	Further information relating to operating lease expense and other operating lease information are as follows: For the Three Months Ended (In thousands) 2021 2020 Leases: Lease cost $ 11,264 $ 11,236 Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows $ 11,377 $ 10,830 Right-of-use assets obtained in exchange for new lease liabilities $ 30 $ 1,612
Supplemental Balance Sheet Information	As of March 31 ($ in thousands) 2021 2020 Right-of-use assets $ 156,942 $ 184,544 Lease liabilities $ 195,590 $ 224,189 Weighted-average remaining lease term 6.73 years 6.95 years Weighted-average discount rate 5.94 % 5.95 %
Maturities of Operating Lease Liabilities	Contractual maturities of the Company’s future minimum lease payments are as follows: (In thousands) March 31, 2021 Contractual Maturities: 2021 $ 35,596 2022 41,887 2023 38,218 2024 31,694 2025 22,881 Thereafter 56,217 Total undiscounted future minimum lease payments 226,493 Less: Discount impact (30,903) Total lease liability $ 195,590

Business Segments (Tables)

Business Segments (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Financial Information Of Company Operating Segments	Revenues (In thousands) Earned Investment Other Total (2) Pre-Tax Income (Loss) Net Income (Loss) to Common Stockholders Three months ended March 31, 2021 Insurance $ 1,604,979 $ 105,237 $ 8,279 $ 1,718,495 $ 257,109 $ 198,708 Reinsurance & Monoline Excess 244,977 37,708 — 282,685 68,649 54,471 Corporate, other and eliminations (3) — 15,632 105,218 120,850 (64,529) (52,606) Net investment gains — — 34,839 34,839 34,839 28,952 Total $ 1,849,956 $ 158,577 $ 148,336 $ 2,156,869 $ 296,068 $ 229,525 Three months ended March 31, 2020 Insurance $ 1,484,955 $ 123,458 $ 8,473 $ 1,616,886 $ 175,947 $ 140,117 Reinsurance & Monoline Excess 206,463 37,710 — 244,173 36,514 29,187 Corporate, other and eliminations (3) — 13,595 113,130 126,725 (41,755) (33,755) Net investment losses — — (177,174) (177,174) (177,174) (139,967) Total $ 1,691,418 $ 174,763 $ (55,571) $ 1,810,610 $ (6,468) $ (4,418) _________________ (1) Certain amounts included in earned premiums of each segment are related to inter-segment transactions. (2) Revenues for Insurance from foreign countries for the three months ended March 31, 2021 and 2020 were $196 million and $168 million, respectively. Revenues for Reinsurance & Monoline Excess from foreign countries for the three months ended March 31, 2021 and 2020 were $88 million and $69 million, respectively.
Identifiable Assets By Segment	(In thousands) March 31, December 31, Insurance $ 21,985,027 $ 21,702,328 Reinsurance & Monoline Excess 4,678,740 4,654,158 Corporate, other and eliminations 3,127,507 2,215,479 Consolidated $ 29,791,274 $ 28,571,965
Net Premiums Earned By Major Line Of Business	Net premiums earned by major line of business are as follows: For the Three Months (In thousands) 2021 2020 Insurance: Other liability $ 601,902 $ 547,129 Short-tail lines (1) 324,740 295,478 Workers' compensation 267,449 301,600 Commercial automobile 220,761 189,643 Professional liability 190,128 151,105 Total Insurance 1,604,979 1,484,955 Reinsurance & Monoline Excess: Casualty reinsurance 149,638 122,731 Property reinsurance 49,466 41,571 Monoline excess (2) 45,873 42,161 Total Reinsurance & Monoline Excess 244,977 206,463 Total $ 1,849,956 $ 1,691,418 ______________ (1) Short-tail lines include commercial multi-peril (non-liability), inland marine, accident and health, fidelity and surety, boiler and machinery and other lines.

General (Details)

General (Details)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Federal Income Tax Rate	21.00%

Per Share Data (Narrative) (Det

Per Share Data (Narrative) (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Weighted average number of shares held in grantor trust (in shares)	7,767,874,000	7,575,168
Antidilutive securities excluded from computation of earnings per share, amount (in shares)		2,000,000

Per Share Data (Weighted Averag

Per Share Data (Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Basic (shares)	185,195	190,287
Diluted (shares)	186,830	190,287

Consolidated Statements of Co_4

Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	$ 6,325,797
Other comprehensive loss	(86,080)	$ (357,175)
End of period	6,430,284
Net realized and unrealized gains (losses) on investments	51,759	(143,285)
Income (loss) before income taxes	296,068	(6,468)
Tax effect	(64,352)	2,942
Net income (loss) before noncontrolling interests	231,716	(3,526)
Total change in unrealized investment losses	(113,735)	(332,850)
Net change in period	4,050	(98,194)
Other comprehensive income (loss), pre-tax	(109,685)	(431,044)
Other comprehensive income (loss), tax effect	23,605	73,869
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(62,172)	(257,299)
Other comprehensive income (loss) before reclassifications	(94,941)	(396,725)
Amounts reclassified from AOCI	8,861	39,550
Other comprehensive loss	(86,080)	(357,175)
Unrealized investment loss related to noncontrolling interest	0	1
End of period	(148,252)	(589,521)
Accumulated Other Comprehensive Income (Loss) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income (loss) before income taxes	11,216	50,063
Tax effect	(2,355)	(10,513)
Net income (loss) before noncontrolling interests	8,861	39,550
Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	289,714	124,514
Other comprehensive income (loss) before reclassifications	(98,991)	(298,531)
Amounts reclassified from AOCI	8,861	39,550
Other comprehensive loss	(90,130)	(258,981)
Unrealized investment loss related to noncontrolling interest	0	1
End of period	199,584	(109,514)
Total change in unrealized investment losses	(113,735)	(332,850)
Unrealized investment gains, tax effect	23,605	73,869
Unrealized investment gains (losses), after-tax amounts	(90,130)	(258,981)
Unrealized Investment Gains (Losses) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net realized and unrealized gains (losses) on investments	11,216	50,063
Tax effect	(2,355)	(10,513)
Net income (loss) before noncontrolling interests	8,861	39,550
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(351,886)	(381,813)
Other comprehensive income (loss) before reclassifications	4,050	(98,194)
Amounts reclassified from AOCI	0	0
Other comprehensive loss	4,050	(98,194)
Unrealized investment loss related to noncontrolling interest	0	0
End of period	(347,836)	(480,007)
Currency translation adjustment, pre-tax	4,050	(98,194)
Currency translation adjustment, tax effect	0	0
Net change in period	4,050	(98,194)
Currency Translation Adjustments | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income (loss) before income taxes	0	0
Tax effect	0	0
Net income (loss) before noncontrolling interests	0	$ 0
Cumulative effect adjustment resulting from changes in accounting principles | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	24,952
Cumulative effect adjustment resulting from changes in accounting principles | Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	24,952
Cumulative effect adjustment resulting from changes in accounting principles | Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	0
Cumulative Effect, Period Of Adoption, Adjusted Balance | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(232,347)
Cumulative Effect, Period Of Adoption, Adjusted Balance | Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	149,466
Cumulative Effect, Period Of Adoption, Adjusted Balance | Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	$ (381,813)

Statements of Cash Flows (Detai

Statements of Cash Flows (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Interest payments	$ 45,393,000	$ 54,582,000

Investments in Fixed Maturity_3

Investments in Fixed Maturity Securities (Investments in fixed maturity securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total held to maturity, Amortized Cost	$ 73,811	$ 73,572
Held-to-maturity, Allowance for Credit Loss	(730)	(798)	$ (107)	$ 0
Held to maturity, Gross Unrealized Gains	12,074	14,260
Held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	85,155	87,034
Total held to maturity, Carrying Value	73,081	72,774
Total available for sale, Amortized Cost	15,053,169	13,682,286
Available-for-sale, Allowance for Credit Loss	(20,009)	(1,782)	(67,356)	0
Total available for sale, Gross Unrealized Gains	392,971	500,283
Total available for sale, Gross Unrealized Losses	(99,094)	(94,192)
Total available for sale, Fair Value	15,327,037	14,086,595
Total available for sale, Carrying Value	15,327,037	14,086,595
Total investments in fixed maturity securities, Amortized Value	15,126,980	13,755,858
Fixed maturity securities, allowance for credit loss	(20,739)	(2,580)
Total investments in fixed maturity securities, Gross Unrealized Gains	405,045	514,543
Total investments in fixed maturity securities, Gross Unrealized Losses	(99,094)	(94,192)
Total investments in fixed maturity securities, Fair Value	15,412,192	14,173,629
Total investments in fixed maturity securities, Carrying Value	15,400,118	14,159,369
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total held to maturity, Amortized Cost	67,710	67,117
Held-to-maturity, Allowance for Credit Loss	(730)	(798)
Held to maturity, Gross Unrealized Gains	11,150	13,217
Held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	78,130	79,536
Total held to maturity, Carrying Value	66,980	66,319
Total available for sale, Amortized Cost	3,340,743	3,421,579
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	168,031	201,154
Total available for sale, Gross Unrealized Losses	(6,181)	(2,069)
Total available for sale, Fair Value	3,502,593	3,620,664
Total available for sale, Carrying Value	3,502,593	3,620,664
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total held to maturity, Amortized Cost	6,101	6,455
Held-to-maturity, Allowance for Credit Loss	0	0
Held to maturity, Gross Unrealized Gains	924	1,043
Held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	7,025	7,498
Total held to maturity, Carrying Value	6,101	6,455
Total available for sale, Amortized Cost	889,638	813,187
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	19,315	24,664
Total available for sale, Gross Unrealized Losses	(12,215)	(5,238)
Total available for sale, Fair Value	896,738	832,613
Total available for sale, Carrying Value	896,738	832,613
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	541,180	586,020
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	15,449	18,198
Total available for sale, Gross Unrealized Losses	(915)	(347)
Total available for sale, Fair Value	555,714	603,871
Total available for sale, Carrying Value	555,714	603,871
Special revenue
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	2,112,542	2,137,162
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	78,450	96,924
Total available for sale, Gross Unrealized Losses	(3,284)	(714)
Total available for sale, Fair Value	2,187,708	2,233,372
Total available for sale, Carrying Value	2,187,708	2,233,372
State general obligation
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	399,636	417,397
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	28,156	33,407
Total available for sale, Gross Unrealized Losses	(1,059)	0
Total available for sale, Fair Value	426,733	450,804
Total available for sale, Carrying Value	426,733	450,804
Pre-refunded
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	231,235	250,081
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	17,990	21,472
Total available for sale, Gross Unrealized Losses	(465)	(162)
Total available for sale, Fair Value	248,760	271,391
Total available for sale, Carrying Value	248,760	271,391
Corporate backed
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	164,542	206,356
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	8,585	8,755
Total available for sale, Gross Unrealized Losses	(788)	(638)
Total available for sale, Fair Value	172,339	214,473
Total available for sale, Carrying Value	172,339	214,473
Local general obligation
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	432,788	410,583
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	34,850	40,596
Total available for sale, Gross Unrealized Losses	(585)	(555)
Total available for sale, Fair Value	467,053	450,624
Total available for sale, Carrying Value	467,053	450,624
Commercial
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	172,817	181,105
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	6,555	6,725
Total available for sale, Gross Unrealized Losses	(86)	(113)
Total available for sale, Fair Value	179,286	187,717
Total available for sale, Carrying Value	179,286	187,717
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	1,062,455	994,292
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	25,870	31,389
Total available for sale, Gross Unrealized Losses	(12,301)	(5,351)
Total available for sale, Fair Value	1,076,024	1,020,330
Total available for sale, Carrying Value	1,076,024	1,020,330
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	3,952,009	3,218,048
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	10,789	10,035
Total available for sale, Gross Unrealized Losses	(18,160)	(33,497)
Total available for sale, Fair Value	3,944,638	3,194,586
Total available for sale, Carrying Value	3,944,638	3,194,586
Industrial
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	2,986,688	2,456,516
Available-for-sale, Allowance for Credit Loss	(16)	(518)
Total available for sale, Gross Unrealized Gains	88,810	115,926
Total available for sale, Gross Unrealized Losses	(14,819)	(7,449)
Total available for sale, Fair Value	3,060,663	2,564,475
Total available for sale, Carrying Value	3,060,663	2,564,475
Financial
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	1,517,251	1,513,943
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	48,756	62,947
Total available for sale, Gross Unrealized Losses	(1,638)	(987)
Total available for sale, Fair Value	1,564,369	1,575,903
Total available for sale, Carrying Value	1,564,369	1,575,903
Utilities
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	426,213	389,267
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	15,476	31,931
Total available for sale, Gross Unrealized Losses	(2,360)	(33)
Total available for sale, Fair Value	439,329	421,165
Total available for sale, Carrying Value	439,329	421,165
Other
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	153,700	109,353
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	429	696
Total available for sale, Gross Unrealized Losses	(301)	(11)
Total available for sale, Fair Value	153,828	110,038
Total available for sale, Carrying Value	153,828	110,038
Corporate
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	5,083,852	4,469,079
Available-for-sale, Allowance for Credit Loss	(16)	(518)	(6,436)	0
Total available for sale, Gross Unrealized Gains	153,471	211,500
Total available for sale, Gross Unrealized Losses	(19,118)	(8,480)
Total available for sale, Fair Value	5,218,189	4,671,581
Total available for sale, Carrying Value	5,218,189	4,671,581
Foreign government
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	1,072,930	993,268
Available-for-sale, Allowance for Credit Loss	(19,993)	(1,264)	$ (60,920)	$ 0
Total available for sale, Gross Unrealized Gains	19,361	28,007
Total available for sale, Gross Unrealized Losses	(42,419)	(44,448)
Total available for sale, Fair Value	1,029,879	975,563
Total available for sale, Carrying Value	$ 1,029,879	$ 975,563

Investments in Fixed Maturity_4

Investments in Fixed Maturity Securities (HTM Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020	$ 798	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	730	107
Provision for expected credit losses	(68)	38
Allowance for expected credit losses at March 31, 2021	$ 730	107
Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020		69
Cumulative effect adjustment resulting from changes in accounting principles		$ 69

Investments in Fixed Maturity_5

Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance	$ 1,782	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	20,009	67,356
Expected credit losses on securities for which credit losses were not previously recorded	19,006	18,930
Expected credit losses on securities for which credit losses were previously recorded	(774)	16,369
Reduction due to disposals	(5)	(3,588)
Allowance for expected credit losses, ending balance	20,009	67,356
Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance		35,645
Cumulative effect adjustment resulting from changes in accounting principles		35,645
Foreign government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance	1,264	0
Cumulative effect adjustment resulting from changes in accounting principles	1,264	60,920
Expected credit losses on securities for which credit losses were not previously recorded	18,990	12,494
Expected credit losses on securities for which credit losses were previously recorded	(261)	16,369
Reduction due to disposals	0	(3,588)
Allowance for expected credit losses, ending balance	19,993	60,920
Foreign government | Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance		35,645
Cumulative effect adjustment resulting from changes in accounting principles		35,645
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance	518	0
Cumulative effect adjustment resulting from changes in accounting principles	518	6,436
Expected credit losses on securities for which credit losses were not previously recorded	16	6,436
Expected credit losses on securities for which credit losses were previously recorded	(513)	0
Reduction due to disposals	(5)	0
Allowance for expected credit losses, ending balance	$ 16	6,436
Corporate | Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance		0
Cumulative effect adjustment resulting from changes in accounting principles		$ 0

Investments in Fixed Maturity_6

Investments in Fixed Maturity Securities (Amortized cost and fair value of fixed maturity securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 1,778,569
Amortized Cost, Due after one year through five years	6,419,223
Amortized Cost, Due after five years through ten years	3,500,751
Amortized Cost, Due after ten years	2,359,151
Amortized Cost, Mortgaged-backed securities	1,068,556
Total investments in fixed maturity securities, Amortized Value	15,126,250
Fair Value, Due in one year or less	1,765,769
Fair Value, Due after one year through five years	6,576,943
Fair Value, Due after five years through ten years	3,592,140
Fair Value, Due after ten years	2,394,291
Fair Value, Mortgage-backed securities	1,083,049
Total investments in fixed maturity securities, Fair Value	15,412,192	$ 14,173,629
Cumulative effect adjustment resulting from changes in accounting principles	$ 730	$ 798	$ 107	$ 0

Investments in Equity Securit_3

Investments in Equity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 621,629	$ 625,667
Fair Value
Debt Securities, Available-for-sale [Line Items]
Cost	536,311	516,014
Gross Unrealized, Gains	94,289	124,323
Gross Unrealized, Losses	(8,971)	(14,670)
Equity securities	621,629	625,667
Fair Value | Common stock
Debt Securities, Available-for-sale [Line Items]
Cost	339,742	335,617
Gross Unrealized, Gains	60,766	28,742
Gross Unrealized, Losses	(8,345)	(14,178)
Equity securities	392,163	350,181
Fair Value | Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Cost	196,569	180,397
Gross Unrealized, Gains	33,523	95,581
Gross Unrealized, Losses	(626)	(492)
Equity securities	229,466	275,486
Carrying Value
Debt Securities, Available-for-sale [Line Items]
Equity securities	621,629	625,667
Carrying Value | Common stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	392,163	350,181
Carrying Value | Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 229,466	$ 275,486

Arbitrage Trading Account (Deta

Arbitrage Trading Account (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Arbitrage trading account	$ 614,721,000	$ 341,473,000
Short | Options held
Derivative [Line Items]
Fair value of derivative	161,000
Notional amount of derivative	$ 18,500,000

Net Investment Income (Details)

Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net Investment Income [Line Items]
Gross investment income	$ 160,027	$ 177,392
Investment expense	(1,450)	(2,629)
Net investment income	158,577	174,763
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Gross investment income	94,677	128,018
Investment funds
Net Investment Income [Line Items]
Gross investment income	38,935	40,577
Arbitrage trading account
Net Investment Income [Line Items]
Gross investment income	19,074	1,138
Equity securities
Net Investment Income [Line Items]
Gross investment income	1,161	6,096
Real estate
Net Investment Income [Line Items]
Gross investment income	$ 6,180	$ 1,563

Investment Funds (Details)

Investment Funds (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Unfunded commitments	$ 129,000
Investment funds	1,358,997		$ 1,309,430
Income from Investment Funds	38,935	$ 40,577
Written premiums ceded	$ 434,674	385,526
Lifson Re
Schedule of Equity Method Investments [Line Items]
Percentage of reinsurance placements of share placed amounts	22.50%
Written premiums ceded	$ 53,000
Financial services
Schedule of Equity Method Investments [Line Items]
Investment funds	304,461		310,783
Income from Investment Funds	4,434	6,790
Real Estate
Schedule of Equity Method Investments [Line Items]
Investment funds	477,927		434,437
Income from Investment Funds	17,142	15,209
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds	143,852		140,935
Income from Investment Funds	3,320	4,413
Transportation
Schedule of Equity Method Investments [Line Items]
Investment funds	193,401		190,125
Income from Investment Funds	6,228	2,646
Other funds
Schedule of Equity Method Investments [Line Items]
Investment funds	239,356		$ 233,150
Income from Investment Funds	$ 7,811	$ 11,519

Real Estate (Details)

Real Estate (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Real Estate [Abstract]
Properties in operation	$ 1,737,394	$ 1,738,144
Properties under development	223,818	222,770
Total	$ 1,961,212	$ 1,960,914

Real Estate (Narrative) (Detail

Real Estate (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Accumulated depreciation and amortization on properties	$ 90,424,000		$ 86,970,000
Real estate depreciation expense	4,890,000	$ 6,620,000
Lease future minimum payments 2020	51,375,848
Lease future minimum payments 2021	69,979,774
Lease future minimum payments 2022	62,948,942
Lease future minimum payments 2023	59,715,831
Lease future minimum payments 2024	55,715,947
Lease future minimum payments 2025	51,654,944
Lease future minimum payments there after	594,894,205
Secured Debt
Debt Instrument [Line Items]
Fae value of debt	$ 101,750,000
Interest rate, percent	4.21%

Loans Receivable (Details)

Loans Receivable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	$ 76,896	$ 84,913
Loans receivable	78,504	86,596
Loans in nonaccrual status	200	200
Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	51,717	51,910
Loans receivable	53,325	53,593
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	25,179	33,003
Loans receivable	$ 25,179	$ 33,003
Loans receivable maturity term	10 years

Loans Receivable - Allowance Fo

Loans Receivable - Allowance For Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses at December 31, 2020	$ 5,437	$ 2,146
Cumulative effect adjustment resulting from changes in accounting principles	5,437	3,928
Provision for expected credit losses	(1,239)	2,139
Allowance for expected credit losses at March 31, 2021	4,198	3,928
Real estate loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses at December 31, 2020	1,683	1,502
Cumulative effect adjustment resulting from changes in accounting principles	1,608	1,435
Provision for expected credit losses	(75)	838
Allowance for expected credit losses at March 31, 2021	1,608	1,435
Commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses at December 31, 2020	3,754	644
Cumulative effect adjustment resulting from changes in accounting principles	2,590	2,493
Provision for expected credit losses	(1,164)	1,301
Allowance for expected credit losses at March 31, 2021	$ 2,590	2,493
Cumulative effect adjustment resulting from changes in accounting principles
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses at December 31, 2020		(357)
Cumulative effect adjustment resulting from changes in accounting principles		(357)
Cumulative effect adjustment resulting from changes in accounting principles | Real estate loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses at December 31, 2020		(905)
Cumulative effect adjustment resulting from changes in accounting principles		(905)
Cumulative effect adjustment resulting from changes in accounting principles | Commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses at December 31, 2020		548
Cumulative effect adjustment resulting from changes in accounting principles		$ 548

Net Investment Gains (Losses)_2

Net Investment Gains (Losses) (Net Investment Gains (Losses)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Fixed maturity securities, gains	$ 8,240	$ 4,931
Fixed maturity securities, losses	(2,071)	(4,847)
Net realized gains on investment sales	8,572	0
Change in unrealized losses	(24,335)	(154,467)
Investment funds	47,671	30,183
Real estate	12,909	(687)
Other	773	(18,398)
Net realized and unrealized gains (losses) on investments in earnings before allowance for expected credit losses	51,759	(143,285)
Fixed maturity securities	(18,159)	(31,750)
Loans receivable	1,239	(2,139)
Change in allowance for expected credit losses on investments	(16,920)	(33,889)
Net investment gains (losses)	34,839	(177,174)
Income tax (expense) benefit	(5,887)	37,207
After-tax net investment gains (losses)	$ 28,952	$ (139,967)

Net Investment Gains (Losses)_3

Net Investment Gains (Losses) (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment losses	$ (113,735)	$ (332,850)
Income tax benefit	23,605	73,869
Noncontrolling interests	0	1
Total change in unrealized gains	(90,130)	(258,980)
Debt securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment losses	(122,568)	(326,416)
Fixed maturity securities with allowance for expected credit losses
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment losses	10,355	1,541
Investment funds
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment losses	(1,020)	(7,646)
Other
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment losses	$ (502)	$ (329)

Fixed Maturity Securities In _3

Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 4,195,463	$ 2,552,830
Gross Unrealized Losses, Less than 12 Months	47,863	42,788
Fair Value, 12 Months or Greater	837,540	747,568
Gross Unrealized Losses, 12 Months or Greater	51,231	51,404
Fair Value, Total	5,033,003	3,300,398
Gross Unrealized Losses, Total	99,094	94,192
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	57,625	47,649
Gross Unrealized Losses, Less than 12 Months	913	347
Fair Value, 12 Months or Greater	462	17
Gross Unrealized Losses, 12 Months or Greater	2	0
Fair Value, Total	58,087	47,666
Gross Unrealized Losses, Total	915	347
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	288,083	147,754
Gross Unrealized Losses, Less than 12 Months	4,949	1,165
Fair Value, 12 Months or Greater	20,219	20,528
Gross Unrealized Losses, 12 Months or Greater	1,232	904
Fair Value, Total	308,302	168,282
Gross Unrealized Losses, Total	6,181	2,069
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	322,410	212,388
Gross Unrealized Losses, Less than 12 Months	11,927	5,121
Fair Value, 12 Months or Greater	30,537	23,943
Gross Unrealized Losses, 12 Months or Greater	374	230
Fair Value, Total	352,947	236,331
Gross Unrealized Losses, Total	12,301	5,351
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,803,588	1,389,133
Gross Unrealized Losses, Less than 12 Months	4,917	6,563
Fair Value, 12 Months or Greater	652,450	656,877
Gross Unrealized Losses, 12 Months or Greater	13,243	26,934
Fair Value, Total	2,456,038	2,046,010
Gross Unrealized Losses, Total	18,160	33,497
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,414,453	612,177
Gross Unrealized Losses, Less than 12 Months	15,904	6,721
Fair Value, 12 Months or Greater	113,498	39,985
Gross Unrealized Losses, 12 Months or Greater	3,214	1,759
Fair Value, Total	1,527,951	652,162
Gross Unrealized Losses, Total	19,118	8,480
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	309,304	143,729
Gross Unrealized Losses, Less than 12 Months	9,253	22,871
Fair Value, 12 Months or Greater	20,374	6,218
Gross Unrealized Losses, 12 Months or Greater	33,166	21,577
Fair Value, Total	329,678	149,947
Gross Unrealized Losses, Total	$ 42,419	$ 44,448

Fixed Maturity Securities In _4

Fixed Maturity Securities In An Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) $ in Thousands	Mar. 31, 2021USD ($)position	Dec. 31, 2020USD ($)
Corporate
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	$ 1,527,951	$ 652,162
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	352,947	236,331
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Aggregate Fair Value	$ 2,456,038	$ 2,046,010
Noninvestment Grade Investments at Loss Position
Debt Securities, Available-for-sale [Line Items]
Number of Securities | position	32
Aggregate Fair Value	$ 105,367
Gross Unrealized Loss	$ 41,789
Noninvestment Grade Investments at Loss Position | Foreign government
Debt Securities, Available-for-sale [Line Items]
Number of Securities | position	19
Aggregate Fair Value	$ 79,761
Gross Unrealized Loss	$ 39,694
Noninvestment Grade Investments at Loss Position | Corporate
Debt Securities, Available-for-sale [Line Items]
Number of Securities | position	8
Aggregate Fair Value	$ 25,066
Gross Unrealized Loss	$ 2,071
Noninvestment Grade Investments at Loss Position | Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of Securities | position	5
Aggregate Fair Value	$ 540
Gross Unrealized Loss	$ 24

Fair Value Measurements (Assets

Fair Value Measurements (Assets and Liabilities Measured At Fair Value, On a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Total fixed maturity securities available for sale	$ 15,327,037	$ 14,086,595
Equity securities	621,629	625,667
Arbitrage trading account	614,721	341,473
Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	15,327,037	14,086,595
Equity securities	621,629	625,667
Arbitrage trading account	614,721	341,473
Assets, fair value disclosure	16,563,387	15,053,735
Liabilities:
Trading account securities sold but not yet purchased	218	10,048
Fair Value, Measurements, Recurring | U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	555,714	603,871
Fair Value, Measurements, Recurring | State and municipal
Assets:
Total fixed maturity securities available for sale	3,502,593	3,620,664
Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets:
Total fixed maturity securities available for sale	1,076,024	1,020,330
Fair Value, Measurements, Recurring | Asset-backed
Assets:
Total fixed maturity securities available for sale	3,944,638	3,194,586
Fair Value, Measurements, Recurring | Corporate
Assets:
Total fixed maturity securities available for sale	5,218,189	4,671,581
Fair Value, Measurements, Recurring | Foreign government
Assets:
Total fixed maturity securities available for sale	1,029,879	975,563
Fair Value, Measurements, Recurring | Common stocks
Assets:
Equity securities	392,163	350,181
Fair Value, Measurements, Recurring | Preferred stocks
Assets:
Equity securities	229,466	275,486
Level 1 | Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	0	0
Equity securities	382,822	340,966
Arbitrage trading account	498,401	298,359
Assets, fair value disclosure	881,223	639,325
Liabilities:
Trading account securities sold but not yet purchased	218	10,048
Level 1 | Fair Value, Measurements, Recurring | U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 | Fair Value, Measurements, Recurring | State and municipal
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 | Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 | Fair Value, Measurements, Recurring | Asset-backed
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 | Fair Value, Measurements, Recurring | Corporate
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 | Fair Value, Measurements, Recurring | Foreign government
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 | Fair Value, Measurements, Recurring | Common stocks
Assets:
Equity securities	382,822	340,966
Level 1 | Fair Value, Measurements, Recurring | Preferred stocks
Assets:
Equity securities	0	0
Level 2 | Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	15,327,037	14,085,595
Equity securities	220,135	266,155
Arbitrage trading account	116,320	43,114
Assets, fair value disclosure	15,663,492	14,394,864
Liabilities:
Trading account securities sold but not yet purchased	0	0
Level 2 | Fair Value, Measurements, Recurring | U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	555,714	603,871
Level 2 | Fair Value, Measurements, Recurring | State and municipal
Assets:
Total fixed maturity securities available for sale	3,502,593	3,620,664
Level 2 | Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets:
Total fixed maturity securities available for sale	1,076,024	1,020,330
Level 2 | Fair Value, Measurements, Recurring | Asset-backed
Assets:
Total fixed maturity securities available for sale	3,944,638	3,194,586
Level 2 | Fair Value, Measurements, Recurring | Corporate
Assets:
Total fixed maturity securities available for sale	5,218,189	4,670,581
Level 2 | Fair Value, Measurements, Recurring | Foreign government
Assets:
Total fixed maturity securities available for sale	1,029,879	975,563
Level 2 | Fair Value, Measurements, Recurring | Common stocks
Assets:
Equity securities	0	0
Level 2 | Fair Value, Measurements, Recurring | Preferred stocks
Assets:
Equity securities	220,135	266,155
Level 3 | Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	0	1,000
Equity securities	18,672	18,546
Arbitrage trading account	0	0
Assets, fair value disclosure	18,672	19,546
Liabilities:
Trading account securities sold but not yet purchased	0	0
Level 3 | Fair Value, Measurements, Recurring | U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 | Fair Value, Measurements, Recurring | State and municipal
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 | Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 | Fair Value, Measurements, Recurring | Asset-backed
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 | Fair Value, Measurements, Recurring | Corporate
Assets:
Total fixed maturity securities available for sale	0	1,000
Level 3 | Fair Value, Measurements, Recurring | Foreign government
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 | Fair Value, Measurements, Recurring | Common stocks
Assets:
Equity securities	9,341	9,215
Level 3 | Fair Value, Measurements, Recurring | Preferred stocks
Assets:
Equity securities	$ 9,331	$ 9,331

Fair Value Measurements (Summar

Fair Value Measurements (Summarize Changes in Level 3 Assets) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, impairments		$ 0
Securities transferred into or out of level 3, net	$ 0
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	19,546,000	15,558,000
Assets, earnings	127,000	1,073,000
Assets, other comprehensive income	0	0
Impairment of Intangible Assets (Excluding Goodwill)	0
Assets, purchases	0	3,000,000
Assets, (sales)	(1,001,000)	(1,085,000)
Assets, maturities	0
Assets. transfers out		1,000,000
Securities transferred into or out of level 3, net	0
Assets, ending balance	18,672,000	19,546,000
Level 3 | Debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	1,000,000	0
Assets, earnings	0	0
Assets, other comprehensive income	0	0
Impairment of Intangible Assets (Excluding Goodwill)	0
Assets, impairments		0
Assets, purchases	0	0
Assets, (sales)	(1,000,000)	0
Assets, maturities	0
Assets. transfers out		1,000,000
Securities transferred into or out of level 3, net	0
Assets, ending balance	0	1,000,000
Level 3 | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	18,546,000	15,558,000
Assets, earnings	126,000	1,054,000
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	3,000,000
Assets, (sales)	0	(1,066,000)
Assets, maturities		0
Assets. transfers out	0	0
Assets, ending balance	18,672,000	18,546,000
Level 3 | Common stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	9,215,000	9,053,000
Assets, earnings	126,000	1,228,000
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	0
Assets, (sales)	0	(1,066,000)
Assets. transfers out	0	0
Assets, ending balance	9,341,000	9,215,000
Level 3 | Preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	9,331,000	6,505,000
Assets, earnings	0	(174,000)
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	3,000,000
Assets, (sales)	0	0
Assets. transfers out	0	0
Assets, ending balance	9,331,000	9,331,000
Level 3 | Arbitrage trading account
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	0	0
Assets, earnings	1,000	19,000
Assets, other comprehensive income	0	0
Impairment of Intangible Assets (Excluding Goodwill)	0
Assets, impairments		0
Assets, purchases	0	0
Assets, (sales)	(1,000)	(19,000)
Assets, maturities	0
Securities transferred into or out of level 3, net	0
Assets, ending balance	0	0
Level 3 | Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	1,000,000	0
Assets, earnings	0	0
Assets, other comprehensive income	0	0
Impairment of Intangible Assets (Excluding Goodwill)	0	0
Assets, purchases	0	0
Assets, (sales)	(1,000,000)	0
Assets, maturities	0	0
Securities transferred into or out of level 3, net	0	1,000,000
Assets, ending balance	$ 0	$ 1,000,000

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details)	3 Months Ended
	Mar. 31, 2021USD ($)
Fair Value Disclosures [Abstract]
Securities transferred into or out of level 3, net	$ 0

Reserves for Loss and Loss Ex_3

Reserves for Loss and Loss Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves at beginning of period	$ 11,620,393	$ 10,697,998
Net provision for losses and loss expenses:
Claims occurring during the current year	1,115,173	1,097,523
Decrease in estimates for claims occurring in prior years	(859)	433
Loss reserve discount accretion	7,278	9,297
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	1,121,592	1,107,253
Net payments for claims:
Current year	97,586	84,310
Prior years	794,472	864,064
Total	892,058	948,374
Foreign currency translation	(14,779)	(77,167)
Net reserves at end of period	11,620,393	10,697,998	$ 11,835,148	$ 11,620,393	$ 10,785,637
Ceded reserves at end of period			2,245,380		1,946,878
Gross reserves at end of period			$ 14,080,528	13,784,430	$ 12,732,515
Cumulative effect adjustment resulting from changes in accounting principles
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves at beginning of period	0	5,927
Net payments for claims:
Net reserves at end of period	0	5,927		0
Cumulative Effect, Period Of Adoption, Adjusted Balance
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves at beginning of period	11,620,393	10,703,925
Net payments for claims:
Net reserves at end of period	$ 11,620,393	$ 10,703,925		$ 11,620,393

Reserves for Loss and Loss Ex_4

Reserves for Loss and Loss Expenses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Net of loss reserve discounts	$ 5	$ 3
Increase (decrease) in estimates for claims	5	(4)
Adjustment expense	3	4
Liability recognized for best estimate net of reinsurance	204
Liability recognized for best estimate net of reinsurance, reported losses	120
Liability recognized for best estimate net of reinsurance, incurred but not reported (IBNR)	84
Unfavorable reserve development net of premium offsets	3
Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability recognized for best estimate net of reinsurance	183
Liability recognized for best estimate net of reinsurance, current accident year losses	15
Favorable reserve development net of premium offsets	6	7
Reinsurance & Monoline Excess
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability recognized for best estimate net of reinsurance	$ 21
Unfavorable reserve development net of premium offsets		$ 3

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Arbitrage trading account	$ 614,721	$ 341,473
Loans receivable	78,504	86,596
Carrying Value
Assets:
Fixed maturity securities	15,400,118	14,159,369
Equity securities	621,629	625,667
Arbitrage trading account	614,721	341,473
Loans receivable	76,896	84,913
Cash and cash equivalents	2,014,911	2,372,366
Trading account receivables from brokers and clearing organizations	257,756	524,727
Due from broker	0	2,585
Liabilities:
Due to broker	149,295	0
Trading account securities sold but not yet purchased	218	10,048
Senior notes and other debt	2,021,142	1,623,025
Subordinated debentures	1,289,272	1,102,309
Fair Value
Assets:
Fixed maturity securities	15,412,192	14,173,629
Equity securities	621,629	625,667
Arbitrage trading account	614,721	341,473
Loans receivable	78,504	86,596
Cash and cash equivalents	2,014,911	2,372,366
Trading account receivables from brokers and clearing organizations	257,756	524,727
Due from broker	0	2,585
Liabilities:
Due to broker	149,295	0
Trading account securities sold but not yet purchased	218	10,048
Senior notes and other debt	2,191,022	1,892,444
Subordinated debentures	$ 1,364,002	$ 1,202,842

Fair Value Of Financial Instr_4

Fair Value Of Financial Instruments Fair Value of Financial Instruments (Narrative) (Details) - Subordinated Debt - Subsequent Event	1 Months Ended
	May 05, 2021USD ($)
Debt Instrument, Redemption [Line Items]
Subordinated debt, redemption price, amount	$ 290,000,000
Subordinated debt, redemption price, percentage	5.75%

Premiums and Reinsurance Rela_3

Premiums and Reinsurance Related Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Written premiums:
Written premiums, direct	$ 2,177,162	$ 1,964,490
Written premiums, assumed	307,550	266,882
Written premiums, ceded	(434,674)	(385,526)
Total net premiums written	2,050,038	1,845,846
Earned premiums:
Earned premiums, direct	2,003,045	1,829,713
Earned premiums, assumed	259,541	228,214
Earned premiums, ceded	(412,630)	(366,509)
Net premiums earned	1,849,956	1,691,418
Ceded losses and loss expenses incurred	298,740	235,183
Ceded commissions earned	101,680	81,045
Cumulative effect adjustment resulting from changes in accounting principles	$ 7,373	$ 6,800	$ 7,801	$ 690

Premiums and Reinsurance Rela_4

Premiums and Reinsurance Related Information - Premiums and Reinsurance, Allowance For Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020	$ 22,883	$ 19,823
Cumulative effect adjustment resulting from changes in accounting principles	22,883	21,524
Provision for expected credit losses	1,381	431
Allowance for expected credit losses at March 31, 2021	24,264	21,524
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020	7,801	690
Cumulative effect adjustment resulting from changes in accounting principles	7,373	6,800
Reinsurance Recoverable, Credit Loss Expense (Reversal)	(428)	183
Allowance for expected credit losses at March 31, 2021	$ 7,373	6,800
Cumulative effect adjustment resulting from changes in accounting principles
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020		1,270
Cumulative effect adjustment resulting from changes in accounting principles		1,270
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020		5,927
Cumulative effect adjustment resulting from changes in accounting principles		$ 5,927

Restricted Stock Units (Summary

Restricted Stock Units (Summary of Restricted Stock Units Issued) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Share based compensation expense	$ 12,000	$ 12,000
Restricted stock
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Restricted stock units (in units)	590	724
Fair Value	$ 40	$ 57
Minimum | Restricted stock
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Award vesting period	3 years
Maximum | Restricted stock
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Award vesting period	5 years

Leases (Lease Cost) (Details)

Leases (Lease Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Lease cost	$ 11,264	$ 11,236
Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows	11,377	10,830
Right-of-use assets obtained in exchange for new lease liabilities	$ 30	$ 1,612

Leases (Supplemental Balance Sh

Leases (Supplemental Balance Sheet Information) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease, right-of-use asset	$ 156,942	$ 184,544
Operating lease, liability	$ 195,590	$ 224,189
Weighted-average remaining lease term	6 years 8 months 23 days	6 years 11 months 12 days
Weighted-average discount rate	5.94%	5.95%

Leases (Maturities of Operating

Leases (Maturities of Operating Lease Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Remainder of 2019	$ 35,596
2021	41,887
2022	38,218
2023	31,694
2024	22,881
Thereafter	56,217
Total undiscounted future minimum lease payments	226,493
Less: Discount impact	(30,903)
Total lease liability	$ 195,590	$ 224,189

Business Segments (Financial In

Business Segments (Financial Information of Company Operating Segments) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	2
Segment Reporting Information [Line Items]
Earned Premiums (1)	$ 1,849,956	$ 1,691,418
Investment Income	158,577	174,763
Other	148,336	(55,571)
Total revenues	2,156,869	1,810,610
Pre-Tax Income (Loss)	296,068	(6,468)
Net Income (Loss) to Common Stockholders	229,525	(4,418)
Net investment gains	34,839	(177,174)
Net investment gains, net of tax	28,952	(139,967)
Corporate, other and eliminations
Segment Reporting Information [Line Items]
Earned Premiums (1)	0	0
Investment Income	15,632	13,595
Other	105,218	113,130
Total revenues	120,850	126,725
Pre-Tax Income (Loss)	(64,529)	(41,755)
Net Income (Loss) to Common Stockholders	(52,606)	(33,755)
Insurance
Segment Reporting Information [Line Items]
Earned Premiums (1)		1,484,955
Insurance | Operating Segments
Segment Reporting Information [Line Items]
Earned Premiums (1)	1,604,979	1,484,955
Investment Income	105,237	123,458
Other	8,279	8,473
Total revenues	1,718,495	1,616,886
Pre-Tax Income (Loss)	257,109	175,947
Net Income (Loss) to Common Stockholders	198,708	140,117
Reinsurance & Monoline Excess
Segment Reporting Information [Line Items]
Earned Premiums (1)		206,463
Reinsurance & Monoline Excess | Operating Segments
Segment Reporting Information [Line Items]
Earned Premiums (1)	244,977	206,463
Investment Income	37,708	37,710
Other	0	0
Total revenues	282,685	244,173
Pre-Tax Income (Loss)	68,649	36,514
Net Income (Loss) to Common Stockholders	54,471	29,187
Re-insurance - International | Operating Segments
Segment Reporting Information [Line Items]
Total revenues	88,000	69,000
Net investment gains
Segment Reporting Information [Line Items]
Earned Premiums (1)	0	0
Investment Income	0	0
Insurance-International Segment | Operating Segments
Segment Reporting Information [Line Items]
Total revenues	$ 196,000	$ 168,000

Business Segments (Identifiable

Business Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 29,791,274	$ 28,571,965
Operating Segments | Insurance
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	21,985,027	21,702,328
Operating Segments | Reinsurance & Monoline Excess
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	4,678,740	4,654,158
Corporate, other and eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 3,127,507	$ 2,215,479

Business Segments (Net Premiums

Business Segments (Net Premiums Earned By Major Line of Business) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue from External Customer [Line Items]
Net premiums earned	$ 1,849,956	$ 1,691,418
Insurance
Revenue from External Customer [Line Items]
Net premiums earned		1,484,955
Insurance | Operating Segments
Revenue from External Customer [Line Items]
Net premiums earned	1,604,979	1,484,955
Insurance | Other liability
Revenue from External Customer [Line Items]
Net premiums earned	601,902	547,129
Insurance | Short-tail lines
Revenue from External Customer [Line Items]
Net premiums earned	324,740	295,478
Insurance | Workers' compensation
Revenue from External Customer [Line Items]
Net premiums earned	267,449	301,600
Insurance | Commercial automobile
Revenue from External Customer [Line Items]
Net premiums earned	220,761	189,643
Insurance | Professional liability
Revenue from External Customer [Line Items]
Net premiums earned	190,128	151,105
Reinsurance & Monoline Excess
Revenue from External Customer [Line Items]
Net premiums earned		206,463
Reinsurance & Monoline Excess | Operating Segments
Revenue from External Customer [Line Items]
Net premiums earned	244,977	206,463
Reinsurance & Monoline Excess | Casualty reinsurance
Revenue from External Customer [Line Items]
Net premiums earned	149,638	122,731
Reinsurance & Monoline Excess | Monoline excess
Revenue from External Customer [Line Items]
Net premiums earned	45,873	42,161
Reinsurance & Monoline Excess | Property reinsurance
Revenue from External Customer [Line Items]
Net premiums earned	$ 49,466	$ 41,571