Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets [Abstract]
Fixed maturities, available-for-sale (amortized cost of $10,119,406 in 2021 and $9,655,261 in 2020)	$ 10,828,145	$ 10,681,734
Equity securities (cost of $2,758,061 in 2021 and $2,732,998 in 2020)	7,528,817	6,994,110
Short-term investments, available-for-sale (estimated fair value approximates cost)	2,736,982	2,034,099
Total Investments	21,093,944	19,709,943
Cash and cash equivalents	3,882,379	4,341,736
Restricted cash and cash equivalents	615,525	874,913
Receivables	2,254,424	1,930,211
Reinsurance recoverables	6,188,894	5,989,337
Deferred policy acquisition costs	722,865	630,794
Prepaid reinsurance premiums	1,477,997	1,451,858
Goodwill	2,604,820	2,604,624
Intangible assets	1,736,148	1,782,718
Other assets	2,466,033	2,393,920
Total Assets	43,043,029	41,710,054
Liabilities and Equity [Abstract]
Unpaid losses and loss adjustment expenses	16,600,500	16,222,376
Life and annuity benefits	977,647	1,069,986
Unearned premiums	4,838,032	4,433,245
Payables to insurance and reinsurance companies	561,155	493,470
Senior long-term debt and other debt (estimated fair value of $4,096,000 in 2021 and $4,367,000 in 2020)	3,564,949	3,484,023
Other liabilities	3,080,928	2,946,631
Total Liabilities	29,623,211	28,649,731
Redeemable noncontrolling interests	234,654	245,642
Commitments and contingencies
Shareholders' equity:
Preferred Stock	591,891	591,891
Common stock	3,447,614	3,428,340
Retained earnings	8,754,760	8,195,182
Accumulated other comprehensive income	369,679	584,376
Total Shareholders' Equity	13,163,944	12,799,789
Noncontrolling interests	21,220	14,892
Total Equity	13,185,164	12,814,681
Total Liabilities and Equity	$ 43,043,029	$ 41,710,054