Borrowings - Narrative (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) borrower	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
Long-term FHLB advances	$ 2,100,000				$ 2,200,000				$ 2,100,000	$ 2,200,000
Number of borrows matched to FHLB advance | borrower									1
Term of FHLB advances									18 years
Repayment term of FHLB advance									30 years
Loans pledged as collateral	0				0				$ 0	0
FHLB discount window	0				0				0	0
Interest paid, less than $1,000									$ 2,833,000	2,087,000	$ 2,035,000
Alaska limit on borrowing, percent of total assets									15.00%
Alaska limit on borrowing, total assets	224,900,000.0				217,400,000.0				$ 224,900,000.0	217,400,000.0
Securities sold under agreements to repurchase	$ 31,420,000				$ 19,843,000				$ 31,420,000	$ 19,843,000
Percentage paid on securities sold under agreements to repurchase	0.10%				0.08%				0.10%	0.08%
Average balance outstanding	$ 23,700,000				$ 20,100,000				$ 23,700,000	$ 20,100,000
Maximum amount outstanding at any month end									37,100,000	22,400,000
Interest expense on deposits, borrowings and junior subordinated debentures	$ 663,000	$ 706,000	$ 748,000	$ 754,000	$ 642,000	$ 487,000	$ 484,000	$ 440,000	$ 2,871,000	$ 2,053,000	$ 2,040,000
Weighted average interest rate	2.52%				3.51%				2.52%	3.51%	5.13%
Note Agreement With Federal Reserve Bank
Debt Instrument [Line Items]
Loans pledged as collateral	$ 81,000,000								$ 81,000,000
Interest paid, less than $1,000									1,000	$ 1,000
Discount Window
Debt Instrument [Line Items]
Loans pledged as collateral	40,200,000								40,200,000
FHLB and Secured Debt
Debt Instrument [Line Items]
Interest expense on deposits, borrowings and junior subordinated debentures									469,000	184,000	$ 340,000
Line of Credit | RML
Debt Instrument [Line Items]
Current draw on line of credit	$ 0				$ 24,100,000				$ 0	$ 24,100,000
Minimum interest rate									2.875%
Interest rate on line of credit at period end	3.063%				2.875%				3.063%	2.875%
London Interbank Offered Rate (LIBOR) | Line of Credit | RML
Debt Instrument [Line Items]
Basis plus LIBOR									2.625%
FHLB Of Seattle
Debt Instrument [Line Items]
Ratio of line of credit to eligible assets	35.00%								35.00%
Line of credit	$ 189,500,000.0								$ 189,500,000.0
Ratio of line of credit to total assets	13.00%								13.00%
Ration of eligible assets to borrowing capacity	35.00%								35.00%
Additional borrowing capacity	$ 524,800,000								$ 524,800,000