DERIVATIVE FINANCIAL INSTRUMENTS: Derivative Financial Instruments Level 4 (Details) - USD ($) $ in Thousands	Dec. 31, 2015		Dec. 31, 2014
Fair Value
Derivative Asset, Fair Value, Gross Asset	$ 1,388		$ 3,015
Derivative Asset, Fair Value, Gross Liability	(984)		(2,381)
Derivative Asset, Fair Value, Amount Offset Against Collateral	404		634
Derivative Liability, Fair Value, Gross Liability	5,956		5,096
Derivative Liability, Fair Value, Gross Asset	(984)		(1,135)
Derivative Liability, Fair Value, Amount Offset Against Collateral	4,972		3,961
Derivative Asset, Collateral, Obligation to Return Cash, Offset			1,200
Derivatives in a net liability position	5,700
Collateral Already Posted, Aggregate Fair Value	900
Additional Collateral, Aggregate Fair Value	9,000
Other current assets | Energy Related Derivative
Fair Value
Derivative Asset, Fair Value, Gross Asset	999		2,509
Derivative Asset, Fair Value, Gross Liability	(785)	[1]	(2,002)
Derivative Asset, Fair Value, Amount Offset Against Collateral	214		507
Derivative Liability, Fair Value, Gross Liability	785		756
Derivative Liability, Fair Value, Gross Asset	(785)		(756)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0		0
Other current assets | Forward contracts
Fair Value
Derivative Asset, Fair Value, Gross Asset	64		64
Derivative Asset, Fair Value, Gross Liability	0		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	64		64
Other current liabilities | Energy Related Derivative
Fair Value
Derivative Asset, Fair Value, Gross Asset	177		379
Derivative Asset, Fair Value, Gross Liability	(177)		(379)
Derivative Asset, Fair Value, Amount Offset Against Collateral	0		0
Derivative Liability, Fair Value, Gross Liability	5,146		4,335
Derivative Liability, Fair Value, Gross Asset	(177)		(379)	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	4,969		3,956
Other current liabilities | Forward contracts
Fair Value
Derivative Liability, Fair Value, Gross Liability	3		5
Derivative Liability, Fair Value, Gross Asset	0		0
Derivative Liability, Fair Value, Amount Offset Against Collateral	3		5
Other assets | Energy Related Derivative
Fair Value
Derivative Asset, Fair Value, Gross Asset	148
Derivative Asset, Fair Value, Gross Liability	(22)
Derivative Asset, Fair Value, Amount Offset Against Collateral	126
Derivative Liability, Fair Value, Gross Liability	22
Derivative Liability, Fair Value, Gross Asset	(22)
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 0
Other assets | Forward contracts
Fair Value
Derivative Asset, Fair Value, Gross Asset			63
Derivative Asset, Fair Value, Gross Liability			0
Derivative Asset, Fair Value, Amount Offset Against Collateral			$ 63

[1] Current asset and current liability derivative amounts offset include $0.9 million of collateral receivable and $1.2 million of collateral payable and for the periods ending December 31, 2015 and 2014, respectively.