Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Level 3 Inputs (Details) - Significant Unobservable Inputs (Level 3) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 158,496	$ 73,596
Included in net investment income
Total foreign exchange gains	(11)	(3)
Purchases	30,336	83,386
Sales		(948)
Settlements	(455)
Ending balance	$ 164,948	$ 158,496
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 4)
Included in net investment income
Included in other income	$ 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	$ (26,893)	$ (159)
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	Other income
Included in net investment income
Included in other income	$ 2,682	$ 2,624
Direct private equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	88,373	79,807
Included in net investment income
Total foreign exchange gains	(11)	(3)
Purchases	5,123	9,676
Sales		(948)
Settlements	0
Ending balance	66,780	88,373
Direct private equity investments | Included in net investment income
Included in net investment income
Included in other income	188
Direct private equity investments | Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income	(26,893)	(159)
Direct private equity investments | Other income (loss)
Included in net investment income
Included in other income	0	0
Term loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	74,850	0
Included in net investment income
Total foreign exchange gains	0	0
Purchases	25,000	74,850
Sales		0
Settlements	(455)
Ending balance	100,000	74,850
Term loans | Included in net investment income
Included in net investment income
Included in other income	605
Term loans | Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income	0	0
Term loans | Other income (loss)
Included in net investment income
Included in other income	0	0
Other Assets and (Liabilities)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(4,727)	(6,211)
Included in net investment income
Total foreign exchange gains	0	0
Purchases	213	(1,140)
Sales		0
Settlements	0
Ending balance	(1,832)	(4,727)
Other Assets and (Liabilities) | Included in net investment income
Included in net investment income
Included in other income	0
Other Assets and (Liabilities) | Net realized and unrealized gains (losses) on investments
Included in net investment income
Included in other income	0	0
Other Assets and (Liabilities) | Other income (loss)
Included in net investment income
Included in other income	$ 2,682	$ 2,624