Fair Value Measurements and Derivative Instruments (Unrealized Holding Losses) (Details) - USD ($) $ in Thousands	Mar. 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	$ 187,195	$ 180,714
Greater than 12 continuous months, Gross unrealized losses	41,290	44,542
Less than 12 continuous months, Fair Value	22,455	27,131
Less than 12 continuous months, Gross unrealized losses	6,291	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	17,515	17,063
Greater than 12 continuous months, Gross unrealized losses	2,388	2,753
Less than 12 continuous months, Fair Value	10,306	10,061
Less than 12 continuous months, Gross unrealized losses	5,054	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	52,359	48,812
Greater than 12 continuous months, Gross unrealized losses	12,398	13,749
Less than 12 continuous months, Fair Value	1,180	3,508
Less than 12 continuous months, Gross unrealized losses	16	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	1,553	1,520
Less than 12 continuous months, Gross unrealized losses	206	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	117,321	114,839
Greater than 12 continuous months, Gross unrealized losses	26,504	28,040
Less than 12 continuous months, Fair Value	9,416	12,042
Less than 12 continuous months, Gross unrealized losses	$ 1,015	$ 1,430