Quarterly Results Of Operations (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Results Of Operations [Abstract]
Operating revenues	$ 62,934,930	$ 49,405,607	$ 51,554,650	$ 60,793,482	$ 57,741,954	$ 45,132,973	$ 44,622,517	$ 50,250,135	$ 224,688,669	$ 197,747,579	$ 216,421,152
Operating expenses	52,778,100	44,850,594	48,365,752	51,223,238	47,000,307	40,308,301	41,472,710	42,359,071	197,217,684	171,140,389	188,791,558
Net interest	5,575,665	5,569,961	5,535,031	5,520,479	5,341,242	5,427,440	5,247,404	5,385,211	22,201,136	21,401,297	21,814,445
Net operating margins	4,581,165	(1,014,948)	(2,346,133)	4,049,765	5,400,405	(602,768)	(2,097,597)	2,505,853	5,269,849	5,205,893	5,815,149
Nonoperating margins	157,569	207,513	201,916	211,877	231,683	125,332	127,871	123,077	778,875	607,963	687,703
Assignable margins	$ 4,738,734	$ (807,435)	$ (2,144,217)	$ 4,261,642	$ 5,632,088	$ (477,436)	$ (1,969,726)	$ 2,628,930	$ 6,048,724	$ 5,813,856	$ 6,502,852