Fair Value Measurements and Derivative Instruments (Unrealized Holding Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Greater than 12 continuous months, Fair Value	$ 199,879	$ 180,714
Greater than 12 continuous months, Gross unrealized losses	43,605	44,542
Less than 12 continuous months, Fair Value	3,963	27,131
Less than 12 continuous months, Gross unrealized losses	419	7,348
Government and related securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Greater than 12 continuous months, Fair Value	28,030	17,063
Greater than 12 continuous months, Gross unrealized losses	7,018	2,753
Less than 12 continuous months, Fair Value	0	10,061
Less than 12 continuous months, Gross unrealized losses	0	5,457
Corporate debt securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Greater than 12 continuous months, Fair Value	51,948	48,812
Greater than 12 continuous months, Gross unrealized losses	10,466	13,749
Less than 12 continuous months, Fair Value	2,382	3,508
Less than 12 continuous months, Gross unrealized losses	212	232
Commingled fixed income securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Less than 12 continuous months, Fair Value	1,581	1,520
Less than 12 continuous months, Gross unrealized losses	207	229
Mortgage-backed / asset-backed securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Greater than 12 continuous months, Fair Value	119,901	114,839
Greater than 12 continuous months, Gross unrealized losses	26,121	28,040
Less than 12 continuous months, Fair Value	0	12,042
Less than 12 continuous months, Gross unrealized losses	$ 0	$ 1,430

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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