Fair Value Measurements (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	$ 62,717,000		$ 62,717,000		$ 57,399,000
Investment related gains (losses), net	(4,991,000)	$ 2,126,000	$ (10,589,000)	$ 7,277,000
Limited Partnership Funds - Middle Market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments			5 years		10 years
Limited Partnership Funds - Middle Market | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	31,427,000		$ 31,427,000		$ 21,947,000
Limited Partnership Funds - Middle Market | Unfunded Loan Commitment | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	8,233,000		$ 8,233,000		$ 18,712,000
Limited Partnership Funds - Global
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments			0 years		0 years
Limited Partnership Funds - Global | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	8,095,000		$ 8,095,000		$ 10,607,000
Limited Partnership Funds - Global | Unfunded Loan Commitment | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	0		0		$ 0
Limited Partnership Funds - Late-Stage Growth
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments					6 years
Limited Partnership Funds - Late-Stage Growth | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	17,639,000		$ 17,639,000		$ 20,468,000
Limited Partnership Funds - Late-Stage Growth | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments			5 years
Limited Partnership Funds - Late-Stage Growth | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments			7 years
Limited Partnership Funds - Late-Stage Growth | Unfunded Loan Commitment | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	20,000,000		$ 20,000,000		$ 4,459,000
Limited Partnership Funds - Infrastructure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments			11 years		12 years
Limited Partnership Funds - Infrastructure | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	5,293,000		$ 5,293,000		$ 3,016,000
Limited Partnership Funds - Infrastructure | Unfunded Loan Commitment | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	14,462,000		14,462,000		16,653,000
Limited Partnership Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment related gains (losses), net	(4,200,000)	$ 1,300,000	(9,400,000)	$ 5,800,000
Other invested assets, carried at amortized cost basis	0		0		0
Limited Partnership Funds [Member] | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	62,454,000		62,454,000		56,038,000
Limited Partnership Funds [Member] | Unfunded Loan Commitment | Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	$ 42,695,000		$ 42,695,000		$ 39,824,000