BENEFIT PLANS: Defined Benefit Plan, Estimated Future Benefit Payments (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Pension Plan
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 30,086
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	32,529
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	35,156
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	37,795
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	40,527
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	241,079
Senior Management Security Plan
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments in Year One	4,516
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	4,582
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	4,371
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	4,547
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	4,964
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 25,659