Investment Securities - Amortized Cost and Fair Values of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 361,844	$ 337,123
Gross Unrealized Gains	8,017	2,073
Gross Unrealized Losses	(10)	(478)
Estimated Fair Value	369,851	338,718
Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	34,391	40,092
Gross Unrealized Gains	705	554
Gross Unrealized Losses	0	0
Estimated Fair Value	35,096	40,646
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Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	800	600
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	800	600
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	36,799	51,291
Gross Unrealized Gains	1,441	18
Gross Unrealized Losses	0	(184)
Estimated Fair Value	38,240	51,125
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,737	12,081
Gross Unrealized Gains	344	67
Gross Unrealized Losses	0	0
Estimated Fair Value	10,081	12,148
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,766	3,392
Gross Unrealized Gains	138	57
Gross Unrealized Losses	0	0
Estimated Fair Value	2,904	3,449
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	277,351	229,667
Gross Unrealized Gains	5,389	1,377
Gross Unrealized Losses	(10)	(294)
Estimated Fair Value	$ 282,730	$ 230,750