COMMON STOCK: Common Stock, Number of Shares, Par Value and Other Disclosures (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Common Stock, Shares, Issued	50,308,702	50,233,463	50,158,486
Common Stock, Shares, Issued	50,352,051	50,308,702	50,233,463
Continuous equity program
Class of Stock [Line Items]
Shares issued during the year	0	0	0
Shares reserved for future issuance	3,000,000
Dividend reinvestment and stock purchase plan
Class of Stock [Line Items]
Shares issued during the year	0	0	0
Shares reserved for future issuance	2,576,723
401(k) Plan
Class of Stock [Line Items]
Shares issued during the year	0	0	0
Shares reserved for future issuance	3,567,954
Long-term incentive and compensation plan
Class of Stock [Line Items]
Shares issued during the year	43,349	75,239	74,977
Shares reserved for future issuance	1,424,695
Restricted stock plan
Class of Stock [Line Items]
Shares issued during the year	0	0	0
Shares reserved for future issuance	256,154