Schedule I. Summary of Investments Other Than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2022 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	$ 22,220,436
Amount at Which Shown in the Balance Sheet	22,220,436
Fixed maturity investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	15,038,551
Fair Value	14,351,402
Amount at Which Shown in the Balance Sheet	14,351,402
U.S. treasuries
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	7,366,580
Fair Value	7,180,129
Amount at Which Shown in the Balance Sheet	7,180,129
Corporate
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	4,722,029
Fair Value	4,390,568
Amount at Which Shown in the Balance Sheet	4,390,568
Agencies
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	419,997
Fair Value	395,149
Amount at Which Shown in the Balance Sheet	395,149
Non-U.S. government
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	402,276
Fair Value	383,838
Amount at Which Shown in the Balance Sheet	383,838
Residential mortgage-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	776,859
Fair Value	710,429
Amount at Which Shown in the Balance Sheet	710,429
Commercial mortgage-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	232,346
Fair Value	213,987
Amount at Which Shown in the Balance Sheet	213,987
Asset-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	1,118,464
Fair Value	1,077,302
Amount at Which Shown in the Balance Sheet	1,077,302
Short term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost or Cost	4,671,581
Fair Value	4,669,272
Amount at Which Shown in the Balance Sheet	4,669,272
Equity investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	625,058
Amount at Which Shown in the Balance Sheet	625,058
Total other investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	2,494,954
Amount at Which Shown in the Balance Sheet	2,494,954
Catastrophe bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	1,241,468
Amount at Which Shown in the Balance Sheet	1,241,468
Fund investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	1,086,706
Amount at Which Shown in the Balance Sheet	1,086,706
Term loans
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	100,000
Amount at Which Shown in the Balance Sheet	100,000
Direct private equity investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	66,780
Amount at Which Shown in the Balance Sheet	66,780
Investments in other ventures, under equity method
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair Value	79,750
Amount at Which Shown in the Balance Sheet	$ 79,750