Fair Value Measurements and Derivative Instruments (Unrealized Holding Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Greater than 12 continuous months, Fair Value	$ 180,714	$ 202,844
Greater than 12 continuous months, Gross unrealized losses	44,542	7,294
Less than 12 continuous months, Fair Value	27,131	56,743
Less than 12 continuous months, Gross unrealized losses	7,348	1,434
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	17,063	16,018
Greater than 12 continuous months, Gross unrealized losses	2,753	579
Less than 12 continuous months, Fair Value	10,061	15,438
Less than 12 continuous months, Gross unrealized losses	5,457	433
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	48,812	51,385
Greater than 12 continuous months, Gross unrealized losses	13,749	2,658
Less than 12 continuous months, Fair Value	3,508	8,859
Less than 12 continuous months, Gross unrealized losses	232	339
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	1,520	1,692
Less than 12 continuous months, Gross unrealized losses	229	33
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	114,839	135,441
Greater than 12 continuous months, Gross unrealized losses	28,040	4,057
Less than 12 continuous months, Fair Value	12,042	30,754
Less than 12 continuous months, Gross unrealized losses	$ 1,430	$ 629