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, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	105	300
AFS Fair Value - Less Than 12 Months Loss Position	$ 259,972	$ 100,011
AFS Unrealized Losses - Less Than 12 Months Loss Position	(2,911)	(599)
AFS Fair Value - 12 Months or More Loss Position	132,247	621,294
AFS Unrealized Losses - 12 Months or More Loss Position	(2,500)	(23,937)
AFS Fair Value - Loss Position	392,219	721,305
AFS Unrealized Losses	$ (5,411)	$ (24,536)
Number of Holdings, HTM Investments in Unrealized Loss Positions | security		2
HTM Fair Value - Less Than 12 Months Loss Position		$ 509
HTM Unrealized Losses - Less Than 12 Months Loss Position		(5)
HTM Fair Value - 12 Months or More Loss Position		411
HTM Fair Value - 12 Months or More Loss Position		(19)
HTM Fair Value - Loss Position		920
HTM Unrealized Losses		$ (24)
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security	11	114
AFS Fair Value - Less Than 12 Months Loss Position	$ 30,459	$ 36,218
AFS Unrealized Losses - Less Than 12 Months Loss Position	(328)	(281)
AFS Fair Value - 12 Months or More Loss Position	0	28,437
AFS Unrealized Losses - 12 Months or More Loss Position	0	(613)
AFS Fair Value - Loss Position	30,459	64,655
AFS Unrealized Losses	$ (328)	$ (894)
Number of Holdings, HTM Investments in Unrealized Loss Positions | security		2
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	59	117
AFS Fair Value - Less Than 12 Months Loss Position	$ 162,964	$ 46,459
AFS Unrealized Losses - Less Than 12 Months Loss Position	(1,850)	(252)
AFS Fair Value - 12 Months or More Loss Position	63,633	364,430
AFS Unrealized Losses - 12 Months or More Loss Position	(755)	(13,272)
AFS Fair Value - Loss Position	226,597	410,889
AFS Unrealized Losses	$ (2,605)	$ (13,524)
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	35	63
AFS Fair Value - Less Than 12 Months Loss Position	$ 66,549	$ 5,956
AFS Unrealized Losses - Less Than 12 Months Loss Position	(733)	(40)
AFS Fair Value - 12 Months or More Loss Position	68,614	227,461
AFS Unrealized Losses - 12 Months or More Loss Position	(1,745)	(10,031)
AFS Fair Value - Loss Position	135,163	233,417
AFS Unrealized Losses	$ (2,478)	(10,071)
HTM Fair Value - Less Than 12 Months Loss Position		509
HTM Unrealized Losses - Less Than 12 Months Loss Position		(5)
HTM Fair Value - 12 Months or More Loss Position		411
HTM Fair Value - 12 Months or More Loss Position		(19)
HTM Fair Value - Loss Position		920
HTM Unrealized Losses		$ (24)
Subordinated corporate bonds
Debt Securities, Available-for-sale [Line Items]
Number of Holdings, AFS Investments in Unrealized Loss Positions | security		6
AFS Fair Value - Less Than 12 Months Loss Position		$ 11,378
AFS Unrealized Losses - Less Than 12 Months Loss Position		(26)
AFS Fair Value - 12 Months or More Loss Position		966
AFS Unrealized Losses - 12 Months or More Loss Position		(21)
AFS Fair Value - Loss Position		12,344
AFS Unrealized Losses		$ (47)