Investment Securities, Securities Held-to-Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Book value	$ 58,701	$ 60,229	$ 54,412
Gross unrealized gains	812	880	571
Gross unrealized losses	10	12	1
Fair value	59,503	61,097	54,982
Obligations of States and Political Subdivisions [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Book value	58,701	60,229	54,412
Gross unrealized gains	812	880	571
Gross unrealized losses	10	12	1
Fair value	$ 59,503	$ 61,097	$ 54,982