Investments (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
AFS Investments (carried at fair value):
Amortized Cost	$ 913,978	$ 933,399
Unrealized Gains	9,551	1,829
Unrealized Losses	(5,411)	(24,536)
AFS securities	918,118	910,692
HTM Investments (carried at amortized cost):
HTM Amortized Cost	1,302	1,307
Unrealized Gains	57	8
Unrealized Losses	0	(24)
Debt Securities, Held-to-maturity, Fair Value	1,359	1,291
Obligations of states and political subdivisions
AFS Investments (carried at fair value):
Amortized Cost	115,632	94,430
Unrealized Gains	2,779	216
Unrealized Losses	(328)	(894)
AFS securities	118,083	93,752
HTM Investments (carried at amortized cost):
HTM Amortized Cost	1,302	1,307
Unrealized Gains	57	8
Unrealized Losses	0	(24)
Debt Securities, Held-to-maturity, Fair Value	1,359	1,291
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
AFS Investments (carried at fair value):
Amortized Cost	462,593	466,613
Unrealized Gains	3,398	583
Unrealized Losses	(2,605)	(13,524)
AFS securities	463,386	453,672
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
AFS Investments (carried at fair value):
Amortized Cost	325,200	351,958
Unrealized Gains	3,183	1,007
Unrealized Losses	(2,478)	(10,071)
AFS securities	325,905	342,894
Subordinated corporate bonds
AFS Investments (carried at fair value):
Amortized Cost	10,553	20,398
Unrealized Gains	191	23
Unrealized Losses	0	(47)
AFS securities	$ 10,744	$ 20,374

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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