Estimated Fair Values (Assets and Liabilities Carried at Fair Value on a Recurring Basis Significant Unobservable Inputs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 69,685	$ 143,226
Purchases	242,595	35,993
Unrealized net gains included in other comprehensive income	2,898	3,891
Amounts included in net income	(336)	174
Transfers in	1,782	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	(112,599)
Sales / Calls	0	(1,000)
Ending balance	316,624	69,685
Investment securities available for sale	316,624	69,685
Corporate Bond Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in	$ 1,800
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		$ (112,600)