Reserve for Claims and Claim Expenses - Schedule of Claims and Claim Expense Reserves by Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Case Reserves	$ 3,821,053	$ 3,339,544
Additional Case Reserves	2,176,884	2,124,825
IBNR	9,894,636	7,830,261
Total reserve for claims and claim expenses	15,892,573	13,294,630	$ 10,381,138
Property | Operating Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Case Reserves	1,956,688	1,555,210
Additional Case Reserves	2,008,891	1,996,760
IBNR	3,570,253	2,825,718
Total reserve for claims and claim expenses	7,535,832	6,377,688
Casualty and Specialty | Operating Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Case Reserves	1,864,365	1,784,334
Additional Case Reserves	167,993	128,065
IBNR	6,324,383	5,004,543
Total reserve for claims and claim expenses	$ 8,356,741	$ 6,916,942