BENEFIT PLANS: Expected future benefit payments and prescription drug benefits (Details) (Postretirement Benefits, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Postretirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 4,010
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	4,180
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	4,320
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	4,430
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	4,530
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	23,420
Prescription Drug Subsidy Receipts, Year One	480
Prescription Drug Subsidy Receipts, Year Two	520
Prescription Drug Subsidy Receipts, Year Three	560
Prescription Drug Subsidy Receipts, Year Four	620
Prescription Drug Subsidy Receipts, Year Five	670
Prescription Drug Subsidy Receipts, Five Fiscal Years Thereafter	$ 4,360