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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Loans and Related Allowance for Loan Losses (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans	$ 1,177,709,000		$ 1,177,709,000			$ 1,058,323,000
Purchased credit impaired (PCI) loans	27,146,000		27,146,000			32,528,000
Allowance for loan losses	12,328,000	$ 8,393,000	12,328,000	$ 8,393,000	$ 12,238,000	8,429,000	$ 8,819,000	$ 8,983,000
Recoveries	132,000	150,000	453,000	541,000
Interest income recognized on impaired loans	59,000	64,000	175,000	190,000
Estimated interest income	$ 61,000	$ 92,000	$ 152,000	$ 284,000
Number of TDR loans \| loan			19	25
Number of TDR loans defaulted \| loan	0	0	0	1
Total impaired	$ 8,967,000		$ 8,967,000			9,885,000
1-4 family mortgages pledged as collateral to the Federal Bank Home Loan	92,400,000		92,400,000
Impaired Financing Receivable Average Recorded Investment	8,607,000	$ 13,080,000	9,198,000	$ 15,166,000
Total borrowing capacity	$ 76,700,000		76,700,000
Provision For Loan And Lease Losses			$ 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	0	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	$ 85,100,000		$ 85,100,000
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	$ 2,000,000.0		$ 2,000,000.0
Allowance for loan losses	0		0
Guaranteed Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Purchased government-guaranteed loans	$ 11,900,000		$ 11,900,000			$ 12,700,000
Percentage of loans guaranteed by the USDA	100.00%		100.00%			100.00%
Unamortized purchase premium	$ 906,000		$ 906,000			$ 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	27,146,000		27,146,000			32,528,000
Allowance for loan losses	7,345,000	$ 5,778,000	7,345,000	$ 5,778,000	10,037,000	6,290,000	6,624,000	5,660,000
Recoveries	96,000	94,000	290,000	432,000
Interest income recognized on impaired loans	56,000	60,000	166,000	177,000
Total impaired	7,162,000		7,162,000			9,424,000
Impaired Financing Receivable Average Recorded Investment	7,174,000	11,994,000	7,956,000	13,543,000
Provision For Loan And Lease Losses	(2,788,000)	(596,000)	765,000	353,000
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	24,664,000		24,664,000			29,465,000
Allowance for loan losses	2,555,000	2,741,000	2,555,000	2,741,000	3,495,000	2,685,000	2,894,000	2,281,000
Recoveries	14,000	26,000	43,000	244,000
Interest income recognized on impaired loans	20,000	23,000	59,000	68,000
Total impaired	2,821,000		2,821,000			2,981,000
Impaired Financing Receivable Average Recorded Investment	3,044,000	3,376,000	3,028,000	3,499,000
Provision For Loan And Lease Losses	(954,000)	(35,000)	(173,000)	394,000
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	51,000	47,000	51,000	47,000	44,000	38,000	32,000	17,000
Total impaired	51,000		51,000
Impaired Financing Receivable Average Recorded Investment	51,000		26,000
Provision For Loan And Lease Losses	7,000	15,000	13,000	30,000
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	216,000		216,000			232,000
Allowance for loan losses	527,000	250,000	527,000	250,000	499,000	248,000	192,000	371,000
Recoveries		41,000		41,000
Total impaired						2,463,000
Recorded investment				2,600,000
Impaired Financing Receivable Average Recorded Investment		2,510,000	616,000	2,533,000
Provision For Loan And Lease Losses	28,000	17,000	279,000	(162,000)
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	457,000		457,000			490,000
Allowance for loan losses	3,011,000	2,034,000	3,011,000	2,034,000	$ 4,612,000	2,196,000	$ 2,026,000	$ 1,810,000
Recoveries	5,000	7,000	84,000	71,000
Interest income recognized on impaired loans	36,000	37,000	107,000	109,000
Total impaired	3,718,000		3,718,000			$ 3,604,000
Impaired Financing Receivable Average Recorded Investment	3,232,000	3,860,000	3,324,000	4,219,000
Provision For Loan And Lease Losses	$ (1,606,000)	$ 1,000	$ 731,000	$ 430,000