Investments: Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) securities	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) securities	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) securities
Schedule of Available-for-sale Securities [Line Items]
Investments pledged as collateral for FHLB advances	50.00%		50.00%
Investments pledged as collateral for public deposits	$ 14,500,000		$ 14,500,000		$ 14,200,000
Principal repayments on investments available-for-sale	5,400,000	$ 2,800,000	15,200,000	$ 7,500,000
Net gain (loss) on sale of investments	$ 1,000	$ 47,000	$ (20,000)	103,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	18		18		13
Unrealized Loss | securities	57		57		36
Proceeds from Sale of Available-for-sale Securities, Debt
Payments to Acquire Marketable Securities			$ 33,011,000	$ 23,518,000