Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Level 3 Inputs (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 164,948	$ 158,496
Included in net investment income
Total foreign exchange gains (losses)	(5)	(11)
Purchases	1,809	30,336
Settlements	(2,342)	(455)
Ending balance	$ 157,048	$ 164,948
Included in net investment income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net investment income (Note 5)	Net investment income (Note 5)
Included in net investment income
Included in other income (loss)	$ 250	$ 793
Net realized and unrealized gains (losses) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized and unrealized gains (losses) on investments	Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income (loss)	$ (7,120)	$ (26,893)
Other income (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other income (loss)	Other income (loss)
Included in net investment income
Included in other income (loss)	$ (492)	$ 2,682
Direct private equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	66,780	88,373
Included in net investment income
Total foreign exchange gains (losses)	(5)	(11)
Purchases	0	5,123
Settlements	0	0
Ending balance	59,905	66,780
Direct private equity investments | Included in net investment income
Included in net investment income
Included in other income (loss)	250	188
Direct private equity investments | Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income (loss)	(7,120)	(26,893)
Direct private equity investments | Other income (loss)
Included in net investment income
Included in other income (loss)	0	0
Term loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	100,000	74,850
Included in net investment income
Total foreign exchange gains (losses)	0	0
Purchases	0	25,000
Settlements	(2,342)	(455)
Ending balance	97,658	100,000
Term loans | Included in net investment income
Included in net investment income
Included in other income (loss)	0	605
Term loans | Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income (loss)	0	0
Term loans | Other income (loss)
Included in net investment income
Included in other income (loss)	0	0
Other Assets and (Liabilities)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(1,832)	(4,727)
Included in net investment income
Total foreign exchange gains (losses)	0	0
Purchases	1,809	213
Settlements	0	0
Ending balance	(515)	(1,832)
Other Assets and (Liabilities) | Included in net investment income
Included in net investment income
Included in other income (loss)	0	0
Other Assets and (Liabilities) | Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income (loss)	0	0
Other Assets and (Liabilities) | Other income (loss)
Included in net investment income
Included in other income (loss)	$ (492)	$ 2,682