Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Assets [Abstract]
Fixed maturity securities, available-for-sale (amortized cost of $16,959,574 in 2025 and $16,457,723 in 2024)	$ 16,772,408	$ 15,745,539
Equity securities (cost of $3,987,784 in 2025 and $3,887,820 in 2024)	12,330,104	11,784,521
Short-term investments, available-for-sale (estimated fair value approximates cost)	1,894,524	2,524,910
Total Investments	30,997,036	30,054,970
Cash and cash equivalents	3,720,202	3,692,667
Restricted cash and cash equivalents	574,891	499,581
Receivables	4,551,187	3,626,799
Reinsurance recoverables	12,789,658	11,604,844
Deferred policy acquisition costs	975,399	875,710
Prepaid reinsurance premiums	4,564,408	2,947,213
Goodwill	2,826,530	2,735,867
Intangible assets	1,617,193	1,459,620
Other assets	4,174,673	4,400,711
Total Assets	66,791,177	61,897,982
Liabilities and Equity [Abstract]
Unpaid losses and loss adjustment expenses	28,515,391	26,633,094
Life and annuity benefits	611,859	583,273
Unearned premiums	9,073,434	7,063,956
Payables to insurance and reinsurance companies	1,723,784	1,434,901
Senior long-term debt and other debt (estimated fair value of $3,876,000 in 2025 and $3,791,000 in 2024)	4,364,232	4,330,341
Other liabilities	4,634,354	4,383,444
Total Liabilities	48,923,054	44,429,009
Redeemable noncontrolling interests	531,339	540,034
Commitments and contingencies
Shareholders' equity:
Preferred Stock	0	591,891
Common stock	3,659,041	3,560,633
Retained earnings	13,839,880	13,380,456
Accumulated other comprehensive loss	(180,763)	(617,082)
Total Shareholders' Equity	17,318,158	16,915,898
Noncontrolling interests	18,626	13,041
Total Equity	17,336,784	16,928,939
Total Liabilities and Equity	$ 66,791,177	$ 61,897,982