Loans and Related Allowance for Loan Losses (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($) loan	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($) loan	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans	$ 1,165,310,000		$ 1,165,310,000			$ 1,058,323,000
Purchased credit impaired (PCI) loans	29,507,000		29,507,000			32,528,000
Allowance for loan losses	12,238,000	$ 8,819,000	12,238,000	$ 8,819,000	$ 11,819,000	8,429,000		$ 8,661,000	$ 8,983,000
Recoveries	137,000	135,000	321,000	391,000
Interest income recognized on impaired loans	60,000	65,000	122,000	127,000
Estimated interest income	$ 100,000	$ 196,000	$ 168,000	$ 410,000
Number of TDR loans | loan			19	25
Number of TDR loans defaulted | loan	0	0	0	1
Total impaired	$ 9,123,000		$ 9,123,000			9,885,000
1-4 family mortgages pledged as collateral to the Federal Bank Home Loan	94,200,000		94,200,000
Impaired Financing Receivable Average Recorded Investment	9,187,000	$ 16,201,000	9,420,000	$ 16,753,000
Total borrowing capacity	77,400,000		77,400,000
Provision For Loan And Lease Losses	$ 900,000	$ 125,000	$ 4,200,000	$ 125,000
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage of loans guaranteed by the USDA	100.00%		100.00%
Number of TDR loans | loan	1	0	1	0
Financing Receivable, Period of Interest Only Payment Relief			6 months
Pre-modification balance			$ 438,000
Post-modification balance			438,000
Paycheck Protection Program Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans	$ 83,500,000		$ 83,500,000
Percentage of loans guaranteed by the USDA	100.00%		100.00%
Term Of P P P Loans Receivable			2 years
Percentage Of Loans Guaranteed By S B A			100
Unamortized purchase premium	$ 2,300,000		$ 2,300,000
Allowance for loan losses	0		0
Guaranteed Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans	$ 12,000,000.0		$ 12,000,000.0			12,700,000
Percentage of loans guaranteed by the USDA	100.00%		100.00%				100.00%		100.00%
Unamortized purchase premium	$ 940,000		$ 940,000			1,000,000.0
Allowance for loan losses	0		0			0
Mortgage Loans on Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans						854,925,000
Purchased credit impaired (PCI) loans	29,507,000		29,507,000			32,528,000
Allowance for loan losses	10,037,000	$ 6,592,000	10,037,000	$ 6,592,000	8,911,000	6,290,000		6,503,000	$ 5,660,000
Recoveries	50,000	108,000	194,000	338,000
Interest income recognized on impaired loans	57,000	60,000	115,000	118,000
Total impaired	8,061,000		8,061,000			9,424,000
Impaired Financing Receivable Average Recorded Investment	7,837,000	14,373,000	8,365,000	14,874,000
Provision For Loan And Lease Losses	1,076,000	15,000	3,553,000	917,000
Mortgage Loans on Real Estate [Member] | Residential 1-4 Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans						223,538,000
Purchased credit impaired (PCI) loans	26,531,000		26,531,000			29,465,000
Allowance for loan losses	3,495,000	2,894,000	3,495,000	2,894,000	2,935,000	2,685,000		3,339,000	2,281,000
Recoveries	13,000	15,000	29,000	218,000
Interest income recognized on impaired loans	21,000	23,000	43,000	45,000
Total impaired	3,268,000		3,268,000			2,981,000
Impaired Financing Receivable Average Recorded Investment	3,155,000	3,667,000	3,097,000	3,676,000
Provision For Loan And Lease Losses	547,000	(426,000)	781,000	429,000
Mortgage Loans on Real Estate [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans						8,346,000
Allowance for loan losses	44,000		44,000		45,000	38,000		23,000	17,000
Total impaired	51,000		51,000
Impaired Financing Receivable Average Recorded Investment	26,000		17,000
Provision For Loan And Lease Losses	(1,000)	(23,000)	6,000	(17,000)
Mortgage Loans on Real Estate [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans						72,978,000
Purchased credit impaired (PCI) loans	223,000		223,000			232,000
Allowance for loan losses	499,000	192,000	499,000	192,000	267,000	248,000		361,000	371,000
Total impaired						2,463,000
Recorded investment				2,600,000
Impaired Financing Receivable Average Recorded Investment		2,539,000	821,000	2,546,000
Provision For Loan And Lease Losses	232,000	(169,000)	251,000	(179,000)
Mortgage Loans on Real Estate [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans						396,858,000
Purchased credit impaired (PCI) loans	470,000		470,000			490,000
Allowance for loan losses	4,612,000	2,026,000	4,612,000	2,026,000	$ 4,240,000	2,196,000		$ 1,508,000	$ 1,810,000
Recoveries	35,000	57,000	79,000	64,000
Interest income recognized on impaired loans	36,000	37,000	72,000	73,000
Total impaired	3,620,000		3,620,000			$ 3,604,000
Impaired Financing Receivable Average Recorded Investment	3,206,000	4,071,000	3,338,000	4,398,000
Provision For Loan And Lease Losses	$ 337,000	$ 461,000	$ 2,337,000	$ 429,000