Employee Benefit Plans: Components of Net Periodic Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 797	$ 704	$ 852
Interest cost	2,956	2,991	2,969
Expected return on assets	(3,935)	(3,702)	(3,764)
Amortization of prior service cost (credits)	43	43	43
Amortization of transition obligation	0	0	2,609
Recognized net actuarial loss (gain)	2,196	940	0
Net periodic expense	2,057	976	2,709
Supplemental Non-qualified Defined Benefit Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	142	146	133
Expected return on assets	0	0	0
Amortization of prior service cost (credits)	0	0	0
Amortization of transition obligation	0	0	0
Recognized net actuarial loss (gain)	93	45	66
Net periodic expense	235	191	199
Non-pension Defined Benefit Postretirement Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	233	222	216
Interest cost	214	241	239
Expected return on assets	0	0	0
Amortization of prior service cost (credits)	(336)	(335)	(278)
Amortization of transition obligation	0	0	0
Recognized net actuarial loss (gain)	0	0	9
Net periodic expense	$ 111	$ 128	$ 186