SHAREHOLDERS' EQUITY (Details 2) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividends
Diluted earnings per share (in dollars per share)	$ 0.26	$ 0.55	$ 0.26	$ 0.48	$ 0.35	$ 0.56	$ 0.27	$ 0.30	$ 1.55	$ 1.48	$ 1.32
Dividends paid per share (in dollars per share)									$ 1.025	$ 1.005	$ 1.000
Total dividends paid									$ 44,381,000	$ 43,006,000	$ 42,273,000
Retained earnings year-end balance	90,276,000				67,554,000				90,276,000	67,554,000	47,100,000
First quarterly dividend paid excluded from EDE Mortgage covenant									98,000
Cumulative aggregate amount up to which the entity may declare or pay any dividends as per EDE Mortgage covenant									$ 10,750,000
Maximum period for payment of dividend after the related date of declaration or notice of dividend as per EDE Mortgage covenant									60 days
Ratio of total indebtedness to total capitalization	0.625								0.625