LONG-TERM DEBT (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Credit Agreement borrowing capacity	$ 795,000,000
Long-term borrowings	$ 530,000,000	$ 69,775,000
Unsecured Revolving Loan [Member]
Debt Instrument [Line Items]
Maturity date	Aug. 08, 2015
Credit Agreement borrowing capacity	$ 25,000,000
Multi-Draw Term Loan [Member]
Debt Instrument [Line Items]
Credit Agreement borrowing capacity	60,000,000
U. S. Bank [Member]
Debt Instrument [Line Items]
Long-term borrowings		39,800,000
Federal Home Loan Bank [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 530,000,000	$ 30,000,000