Investment Securities Available-for-Sale - Gross unrealized losses and fair value (Details)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of Securities	66,000	148
Less than 12 months, estimated fair value	$ 222,354,000	$ 274,947,000
Less than 12 months, unrealized losses	857,000	1,592,000
12 months or greater, estimated fair value	47,739,000	142,223,000
12 months or greater, unrealized losses	611,000	1,443,000
Estimated Fair Value	270,093,000	417,170,000
Unrealized Losses	$ 1,468,000	$ 3,035,000
U. S. agency securities
Debt Securities, Available-for-sale [Line Items]
Number of Securities	28,000	36
Less than 12 months, estimated fair value	$ 46,412,000	$ 75,159,000
Less than 12 months, unrealized losses	67,000	439,000
12 months or greater, estimated fair value	41,320,000	51,481,000
12 months or greater, unrealized losses	560,000	616,000
Estimated Fair Value	87,732,000	126,640,000
Unrealized Losses	$ 627,000	$ 1,055,000
Residential mortgage backed securities
Debt Securities, Available-for-sale [Line Items]
Number of Securities	35,000	111
Less than 12 months, estimated fair value	$ 170,178,000	$ 197,794,000
Less than 12 months, unrealized losses	782,000	1,148,000
12 months or greater, estimated fair value	6,419,000	90,742,000
12 months or greater, unrealized losses	51,000	827,000
Estimated Fair Value	176,597,000	288,536,000
Unrealized Losses	$ 833,000	$ 1,975,000
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Number of Securities	3,000
Less than 12 months, estimated fair value	$ 5,764,000
Less than 12 months, unrealized losses	8,000
12 months or greater, estimated fair value	0
12 months or greater, unrealized losses	0
Estimated Fair Value	5,764,000
Unrealized Losses	$ 8,000
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Number of Securities | security		1
Less than 12 months, estimated fair value		$ 1,994,000
Less than 12 months, unrealized losses		5,000
12 months or greater, estimated fair value		0
12 months or greater, unrealized losses		0
Estimated Fair Value		1,994,000
Unrealized Losses		$ 5,000