Indebtedness (Details) - USD ($)	1 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2021	Sep. 30, 2021	Feb. 28, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Face Value	$ 102,000,000
Subsidiary Debt
Debt Instrument [Line Items]
Face Value			$ 10,564,000
Carrying Value			10,564,000			$ 110,987,000
Repayments in 2020			4,500,000
Repayments thereafter			6,100,000
Total senior notes and other debt
Debt Instrument [Line Items]
Face Value			2,257,067,000
Carrying Value			$ 2,259,416,000			1,623,025,000
Senior Notes | Senior Notes due January 1, 2022
Debt Instrument [Line Items]
Interest Rate			8.70%
Face Value			$ 76,503,000
Carrying Value			$ 76,503,000			76,419,000
Senior Notes | Senior Notes due March 15, 2022
Debt Instrument [Line Items]
Interest Rate			4.625%
Face Value			$ 350,000,000
Carrying Value			$ 349,923,000			349,505,000
Senior Notes | Senior Notes due February 15, 2037
Debt Instrument [Line Items]
Interest Rate			6.25%
Face Value			$ 250,000,000
Carrying Value			$ 248,336,000			248,226,000
Senior Notes | Senior Notes due August 1, 2044
Debt Instrument [Line Items]
Interest Rate			4.75%
Face Value			$ 350,000,000
Carrying Value			$ 345,836,000			345,652,000
Senior Notes | Senior Notes Due May 12 2050
Debt Instrument [Line Items]
Interest Rate			4.00%
Face Value			$ 470,000,000
Carrying Value			$ 491,478,000			492,236,000
Senior Notes | Senior Notes Due September 30, 2061
Debt Instrument [Line Items]
Interest Rate			3.15%	3.15%
Face Value			$ 350,000,000	$ 350,000,000
Carrying Value			$ 342,761,000			0
Senior Notes | Senior Notes Due March 30, 2052
Debt Instrument [Line Items]
Interest Rate		3.55%	3.55%
Face Value		$ 400,000,000	$ 400,000,000
Carrying Value			394,015,000			0
Total subordinated debentures
Debt Instrument [Line Items]
Face Value			1,035,000,000
Carrying Value			$ 1,007,652,000			1,102,309,000
Total subordinated debentures | Subordinated Debt due March 1, 2056
Debt Instrument [Line Items]
Interest Rate		5.90%	5.90%
Face Value			$ 0
Carrying Value			$ 0			106,365,000
Extinguishment of debt		$ 110,000,000
Total subordinated debentures | Subordinated Debt due June1, 2056
Debt Instrument [Line Items]
Interest Rate	5.75%		5.75%
Face Value			$ 0
Carrying Value			$ 0			282,003,000
Extinguishment of debt	$ 290,000,000
Total subordinated debentures | Subordinated Debt due March 30, 2058
Debt Instrument [Line Items]
Interest Rate			5.70%
Face Value			$ 185,000,000
Carrying Value			$ 179,166,000			179,006,000
Total subordinated debentures | Subordinated Debt due December 30, 2059
Debt Instrument [Line Items]
Interest Rate			5.10%
Face Value			$ 300,000,000
Carrying Value			$ 290,941,000			290,702,000
Total subordinated debentures | Subordinated Debt Due September 30 2060
Debt Instrument [Line Items]
Interest Rate			4.25%
Face Value			$ 250,000,000
Carrying Value			$ 244,378,000			244,233,000
Total subordinated debentures | Subordinated Debt Due March 30, 2061
Debt Instrument [Line Items]
Interest Rate			4.125%		4.125%
Face Value			$ 300,000,000		$ 300,000,000
Carrying Value			293,167,000			$ 0
Non-recourse loan
Debt Instrument [Line Items]
Face Value			$ 102,000,000