Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	$ 17,347	$ 27,294
Private Equity Funds - Middle Market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments	10 years	10 years
Private Equity Funds - Term Liquidity Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments	1 year	3 years
Private Equity 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	7 years	7 years
Private Equity Funds - Infrastructure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Maturity Timeframe of Other Long-Term Investments	12 years	12 years
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Middle Market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	$ 8,457	$ 10,542
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Middle Market | Unfunded Loan Commitment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	31,777	29,783
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Term Liquidity Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	36	1,381
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Term Liquidity Facility | Unfunded Loan Commitment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	0	0
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Late-Stage Growth
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	6,199	0
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Late-Stage Growth | Unfunded Loan Commitment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	14,198	16,291
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Infrastructure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	2,290	0
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds - Infrastructure | Unfunded Loan Commitment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	17,485	17,497
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	16,982	11,923
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds [Member] | Unfunded Loan Commitment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Investments	$ 63,460	$ 63,571