Fair Value Measurements and Derivative Instruments (Unrealized Holding Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 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	$ 191,218	$ 180,714
Greater than 12 continuous months, Gross unrealized losses	57,291	44,542
Less than 12 continuous months, Fair Value	1,500	27,131
Less than 12 continuous months, Gross unrealized losses	278	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	26,071	17,063
Greater than 12 continuous months, Gross unrealized losses	9,054	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	50,820	48,812
Greater than 12 continuous months, Gross unrealized losses	14,451	13,749
Less than 12 continuous months, Fair Value	0	3,508
Less than 12 continuous months, Gross unrealized losses	0	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	1,500	1,520
Less than 12 continuous months, Gross unrealized losses	278	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	114,327	114,839
Greater than 12 continuous months, Gross unrealized losses	33,786	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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-Topic 326
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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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