Quarterly Results Of Operations (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statements Of Operations [Abstract]
Operating revenues	$ 74,483,455	$ 62,675,511	$ 58,631,729	$ 71,180,773	$ 76,828,268	$ 68,778,352	$ 68,517,526	$ 69,494,223	$ 266,971,468	$ 283,618,369	$ 258,325,345
Total operating expenses	68,250,215	60,200,529	55,725,151	64,019,060	70,143,069	65,509,750	65,592,311	61,096,736	248,194,955	262,341,866	233,967,201
Net interest	3,492,044	3,495,865	3,542,676	3,872,346	4,102,750	3,544,204	4,209,482	4,890,541	14,402,931	16,746,977	20,005,698
Net operating margins	2,741,196	(1,020,883)	(636,098)	3,289,367	2,582,449	(275,602)	(1,284,267)	3,506,946	4,373,582	4,529,526	4,352,446
Nonoperating margins	632,775	261,487	123,962	133,701	628,697	161,595	120,363	133,081	1,151,925	1,043,736	1,057,563
Assignable margins	$ 3,373,971	$ (759,396)	$ (512,136)	$ 3,423,068	$ 3,211,146	$ (114,007)	$ (1,163,904)	$ 3,640,027	$ 5,525,507	$ 5,573,262	$ 5,410,009