Investment Securities - Amortized Cost and Fair Values of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 337,123	$ 393,855
Gross Unrealized Gains	2,073	387
Gross Unrealized Losses	(478)	(10,249)
Estimated Fair Value	338,718	383,993
Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	40,092	42,331
Gross Unrealized Gains	554	175
Gross Unrealized Losses	0	(313)
Estimated Fair Value	40,646	42,193
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Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	600	400
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	600	400
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	51,291	55,221
Gross Unrealized Gains	18	0
Gross Unrealized Losses	(184)	(2,327)
Estimated Fair Value	51,125	52,894
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,081	13,159
Gross Unrealized Gains	67	0
Gross Unrealized Losses	0	(258)
Estimated Fair Value	12,148	12,901
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,392	3,635
Gross Unrealized Gains	57	0
Gross Unrealized Losses	0	(97)
Estimated Fair Value	3,449	3,538
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	229,667	279,109
Gross Unrealized Gains	1,377	212
Gross Unrealized Losses	(294)	(7,254)
Estimated Fair Value	$ 230,750	$ 272,067