Investments (Unrealized Gross Losses and Estimated Fair values of Investment Securities by Length of Time that Individual Securities in Each Category in Continuous Loss Position) (Details) $ in Thousands	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	30	105
AFS Fair Value - Less Than 12 Months Loss Position	$ 107,635	$ 259,972
AFS Unrealized Losses - Less Than 12 Months Loss Position	(916)	(2,911)
AFS Fair Value - 12 Months or More Loss Position	980	132,247
AFS Unrealized Losses - 12 Months or More Loss Position	(6)	(2,500)
AFS Fair Value - Loss Position	108,615	392,219
AFS Unrealized Losses	$ (922)	$ (5,411)
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	1	11
AFS Fair Value - Less Than 12 Months Loss Position	$ 2,404	$ 30,459
AFS Unrealized Losses - Less Than 12 Months Loss Position	(115)	(328)
AFS Fair Value - 12 Months or More Loss Position	0	0
AFS Unrealized Losses - 12 Months or More Loss Position	0	0
AFS Fair Value - Loss Position	2,404	30,459
AFS Unrealized Losses	$ (115)	$ (328)
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	15	59
AFS Fair Value - Less Than 12 Months Loss Position	$ 61,222	$ 162,964
AFS Unrealized Losses - Less Than 12 Months Loss Position	(568)	(1,850)
AFS Fair Value - 12 Months or More Loss Position	980	63,633
AFS Unrealized Losses - 12 Months or More Loss Position	(6)	(755)
AFS Fair Value - Loss Position	62,202	226,597
AFS Unrealized Losses	$ (574)	$ (2,605)
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	9	35
AFS Fair Value - Less Than 12 Months Loss Position	$ 39,107	$ 66,549
AFS Unrealized Losses - Less Than 12 Months Loss Position	(135)	(733)
AFS Fair Value - 12 Months or More Loss Position	0	68,614
AFS Unrealized Losses - 12 Months or More Loss Position	0	(1,745)
AFS Fair Value - Loss Position	39,107	135,163
AFS Unrealized Losses	$ (135)	$ (2,478)
Subordinated corporate bonds
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	5
AFS Fair Value - Less Than 12 Months Loss Position	$ 4,902
AFS Unrealized Losses - Less Than 12 Months Loss Position	(98)
AFS Fair Value - 12 Months or More Loss Position	0
AFS Unrealized Losses - 12 Months or More Loss Position	0
AFS Fair Value - Loss Position	4,902
AFS Unrealized Losses	$ (98)