Securities (Summary of Book Values and Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value
Amortized Cost	$ 775,962	$ 812,202
Fair Value	806,470	821,945
Unrealized Gains	30,790	10,505
Unrealized (Losses)	(282)	(762)
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	61,303	67,932
Fair Value	62,385	68,333
Unrealized Gains	1,088	410
Unrealized (Losses)	(6)	(9)
Government-sponsored enterprise securities
Fair Value
Amortized Cost	5,000	20,000
Fair Value	5,032	20,009
Unrealized Gains	32	17
Unrealized (Losses)	0	(8)
Mortgage-backed securities
Fair Value
Amortized Cost	727,261	758,491
Fair Value	756,926	767,285
Unrealized Gains	29,892	9,463
Unrealized (Losses)	(227)	(669)
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	39,113	41,423
Fair Value	39,992	41,542
Unrealized Gains	879	125
Unrealized (Losses)	0	(6)
Corporate bonds
Fair Value
Amortized Cost	43,701	33,711
Fair Value	44,512	34,651
Unrealized Gains	866	1,025
Unrealized (Losses)	(55)	(85)
State and local governments
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	22,190	26,509
Fair Value	22,393	26,791
Unrealized Gains	209	285
Unrealized (Losses)	$ (6)	$ (3)

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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