Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets [Abstract]
Fixed maturities, available-for-sale (amortized cost of $9,601,898 in 2019 and $9,950,773 in 2018)	$ 10,204,025	$ 10,043,188
Equity securities (cost of $3,204,316 in 2019 and $2,971,856 in 2018)	6,978,874	5,720,945
Short-term investments, available-for-sale (estimated fair value approximates cost	1,545,393	1,077,696
Total Investments	18,728,292	16,841,829
Cash and cash equivalents	2,715,455	2,014,168
Restricted cash and cash equivalents	484,314	382,264
Receivables	1,930,394	1,692,526
Reinsurance recoverables	5,372,156	5,221,947
Deferred policy acquisition costs	570,323	474,513
Prepaid reinsurance premiums	1,508,853	1,331,022
Goodwill	2,187,585	2,237,975
Intangible assets	1,659,129	1,726,196
Other assets	1,879,695	1,383,823
Total Assets	37,036,196	33,306,263
Liabilities and Equity [Abstract]
Unpaid losses and loss adjustment expenses	14,437,816	14,276,479
Life and annuity benefits	1,021,185	1,001,453
Unearned premiums	4,224,074	3,611,028
Payables to insurance and reinsurance companies	408,508	337,326
Senior long-term debt and other debt (estimated fair value of $4,257,000 in 2019 and $3,030,000 in 2018)	3,896,962	3,009,577
Other liabilities	2,247,179	1,796,036
Total Liabilities	26,235,724	24,031,899
Redeemable noncontrolling interests	165,602	174,062
Commitments and contingencies
Shareholders' equity:
Common stock	3,402,934	3,392,993
Retained earnings	6,988,888	5,782,310
Accumulated other comprehensive income (loss)	231,632	(94,650)
Total Shareholders' Equity	10,623,454	9,080,653
Noncontrolling interests	11,416	19,649
Total Equity	10,634,870	9,100,302
Total Liabilities and Equity	$ 37,036,196	$ 33,306,263