Loans Receivable: Financing Receivables, Aging of loans (Details) - USD ($)		Dec. 31, 2019		Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Financing Receivable, 90 Days or More Past Due, Still Accruing		$ 0		$ 0
Total		2,184,000		821,000
Current		1,120,054,000		1,036,608,000
Total Loans	[2]	1,122,238,000	[1]	1,037,429,000	[3]
One-to-four family, residential, owner occupied
Financing Receivable, Past Due [Line Items]
Total		79,000		495,000
Current		210,819,000		193,646,000
Total Loans		210,898,000	[1],[2]	194,141,000	[3]
One-to-four family residential non-owner occupied
Financing Receivable, Past Due [Line Items]
Total		0		0
Current		161,630,000		147,825,000
Total Loans		161,630,000	[1],[2]	147,825,000	[3]
Multifamily
Financing Receivable, Past Due [Line Items]
Total		2,105,000		0
Current		170,810,000		169,355,000
Total Loans		172,915,000	[1],[2]	169,355,000	[3]
Commercial Real Estate
Financing Receivable, Past Due [Line Items]
Total		0		326,000
Current		395,152,000		373,472,000
Total Loans		395,152,000	[1],[2]	373,798,000	[3]
Construction Land Development
Financing Receivable, Past Due [Line Items]
Total		0		0
Current		113,665,000		108,854,000
Total Loans		113,665,000	[1],[2]	108,854,000	[3]
Real Estate, Total
Financing Receivable, Past Due [Line Items]
Total		2,184,000		821,000
Current		1,052,076,000		993,152,000
Total Loans		1,054,260,000	[1],[2]	993,973,000	[3]
Business
Financing Receivable, Past Due [Line Items]
Total		0		0
Current		37,779,000		30,486,000
Total Loans		37,779,000	[1],[2]	30,486,000	[3]
Consumer
Financing Receivable, Past Due [Line Items]
Total		0		0
Current		30,199,000		12,970,000
Total Loans		30,199,000	[1],[2]	12,970,000	[3]
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total		2,184,000		223,000
Financial Asset, 30 to 59 Days Past Due [Member] | One-to-four family, residential, owner occupied
Financing Receivable, Past Due [Line Items]
Total		79,000		223,000
Financial Asset, 30 to 59 Days Past Due [Member] | One-to-four family residential non-owner occupied
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 30 to 59 Days Past Due [Member] | Multifamily
Financing Receivable, Past Due [Line Items]
Total		2,105,000		0
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 30 to 59 Days Past Due [Member] | Construction Land Development
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 30 to 59 Days Past Due [Member] | Real Estate, Total
Financing Receivable, Past Due [Line Items]
Total		2,184,000		223,000
Financial Asset, 30 to 59 Days Past Due [Member] | Business
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | One-to-four family, residential, owner occupied
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | One-to-four family residential non-owner occupied
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Multifamily
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Construction Land Development
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Real Estate, Total
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Business
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total		0		598,000
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | One-to-four family, residential, owner occupied
Financing Receivable, Past Due [Line Items]
Total		0		272,000
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | One-to-four family residential non-owner occupied
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Multifamily
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate
Financing Receivable, Past Due [Line Items]
Total		0		326,000
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction Land Development
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Real Estate, Total
Financing Receivable, Past Due [Line Items]
Total		0		598,000
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Business
Financing Receivable, Past Due [Line Items]
Total		0		0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer
Financing Receivable, Past Due [Line Items]
Total		$ 0		$ 0

[1] (1) There were no loans 90 days past due and still accruing interest at December 31, 2018.

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[3] (1) There were no loans 90 days past due and still accruing interest at December 31, 201