Quarterly Financial Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								10 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, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Information [Abstract]
Operating revenue	$ 46,202	$ 47,088	$ 47,141	$ 48,769	$ 46,582	$ 45,813	$ 43,857	$ 46,944	$ 10,783	$ 189,200	$ 183,196	$ 163,538
Operating income	4,469	4,286	5,006	3,857	5,090	4,557	4,487	5,252		17,618	19,386	19,655
Income before income taxes	3,278	3,132	3,888	2,720	3,983	2,935	2,902	3,861		13,018	13,681	13,443
Net Income	1,923	1,862	2,321	1,626	2,525	1,741	1,738	2,294	939	7,732	8,298	8,401
Comprehensive income	$ 2,306	$ 1,733	$ 2,290	$ 1,553	$ 7,564	$ 1,860	$ 1,195	$ 2,373		$ 7,882	$ 12,992	$ 7,809
Basic earnings per share	$ 0.14	$ 0.14	$ 0.17	$ 0.12	$ 0.19	$ 0.13	$ 0.13	$ 0.17		$ 0.57	$ 0.62	$ 0.63
Diluted earnings per share	$ 0.14	$ 0.14	$ 0.17	$ 0.12	$ 0.19	$ 0.13	$ 0.13	$ 0.17	$ 0.07	$ 0.57	$ 0.61	$ 0.63
Dividends per share	$ 0.15	$ 0.145	$ 0.145	$ 0.145	$ 0.145	$ 0.14	$ 0.14	$ 0.14		$ 0.585	$ 0.565	$ 0.545