Fair Value Measurements - Assets and Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Senior Notes | 5.25% Senior Notes due 2028
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate (in hundredths)	5.25%
9% Convertible Junior Subordinated Debentures due 2063
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate (in hundredths)	9.00%	9.00%	9.00%
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	$ 850	$ 850
9% Debentures	0	21,086
Total financial liabilities	643,196	662,810
Carrying Value | Senior Notes | 5.25% Senior Notes due 2028
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	643,196	641,724
Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	850	850
9% Debentures	0	28,085
Total financial liabilities	634,498	629,023
Fair Value | Significant Other Observable Inputs (Level 2) | Senior Notes | 5.25% Senior Notes due 2028
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	$ 634,498	$ 600,938