Financial Assets and Liabilities - Gross Obligations For Securities Lending Transactions (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	$ 1,072,043	$ 1,795,994
Remaining contractual maturity for securities loaned	1,557,661	1,329,446
Overnight and Continuous
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	672,043	1,395,994
Remaining contractual maturity for securities loaned	1,557,661	1,329,446
Less than 30 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	140,000	140,000
Remaining contractual maturity for securities loaned	0	0
30 - 60 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	185,000	185,000
Remaining contractual maturity for securities loaned	0	0
61 - 90 Days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	75,000	75,000
Remaining contractual maturity for securities loaned	0	0
Greater than 90 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	0	0
Remaining contractual maturity for securities loaned	0	0
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	400,000	400,000
Remaining contractual maturity for securities loaned	1,557,661	1,329,446
Equity securities | Overnight and Continuous
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	0	0
Remaining contractual maturity for securities loaned	1,557,661	1,329,446
Equity securities | Less than 30 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	140,000	140,000
Remaining contractual maturity for securities loaned	0	0
Equity securities | 30 - 60 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	185,000	185,000
Remaining contractual maturity for securities loaned	0	0
Equity securities | 61 - 90 Days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	75,000	75,000
Remaining contractual maturity for securities loaned	0	0
Equity securities | Greater than 90 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	0	0
Remaining contractual maturity for securities loaned	0	0
U.S. and Non-U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	672,043	1,395,994
U.S. and Non-U.S. government obligations | Overnight and Continuous
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	672,043	1,395,994
U.S. and Non-U.S. government obligations | Less than 30 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	0	0
U.S. and Non-U.S. government obligations | 30 - 60 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	0	0
U.S. and Non-U.S. government obligations | 61 - 90 Days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	0	0
U.S. and Non-U.S. government obligations | Greater than 90 days
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contractual maturity for securities sold under agreements to repurchase	$ 0	$ 0