SELECTED CONSOLIDATED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of quarterly unaudited consolidated statements of operations information [Abstract]
Operating revenues	$ 16,893	$ 18,073	$ 17,780	$ 16,327	$ 16,952	$ 19,001	$ 17,912	$ 16,698	$ 69,073	$ 70,563	$ 65,070
Operating income	3,277	4,324	4,145	2,738	3,479	4,495	4,294	3,590	14,484	15,855	13,736
Net income applicable to common stock	$ 1,547	$ 2,602	$ 2,512	$ 1,640	$ 1,748	$ 2,846	$ 2,748	$ 2,505	$ 8,301	$ 9,846	$ 6,746
Income per common share [Abstract]
Basic (in dollars per share)	$ 0.18	$ 0.30	$ 0.29	$ 0.19	$ 0.20	$ 0.33	$ 0.32	$ 0.29	$ 0.95	$ 1.14	$ 0.83
Diluted (in dollars per share)	$ 0.17	$ 0.29	$ 0.28	$ 0.19	$ 0.20	$ 0.33	$ 0.32	$ 0.29	$ 0.94	$ 1.13	$ 0.83