COMMON STOCK (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning of Year	68,334,860	65,430,084	63,306,524
New Issues During Year:
Dividend Reinvestment Plan	2,604,424	2,881,556	1,966,834
Stock-Based Compensation Plan	26,338	23,220	156,726
End of Year	70,965,622	68,334,860	65,430,084
Par value of common stock (in USD per share)	$ 1.25	$ 1.25
Net excess over par value recorded in premium on common stock (in USD)	$ 61,100
Incremental shares included in diluted earnings per share (in shares)	195,139	150,062	115,520
Dividend per share (in USD per share)	$ 1.02	$ 0.96	$ 0.9
Equity capital raised through Dividend Reinvestment Plan (in USD)	$ 63,192	$ 80,680	$ 54,028