Maintenance Reserves and Accrued Maintenance Costs (1) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Accrued maintenance cost [Roll Forward]
Balance, beginning of period	$ 878,700	$ 1,013,400
Additions [Abstract]
Charged to expense	6,239,900	3,174,500
Capital equipment	384,800	52,300
Accrued claims related to refundable maintenance reserves	605,900	578,100
Prepaid maintenance and other	134,100	333,500
Total additions	7,364,700	4,138,400
Deductions [Abstract]
Payments	4,770,000	3,233,900
Other	803,700	292,400
Total deductions	5,573,700	3,526,300
Net increase in accrued maintenance costs	1,791,000	612,100
Balance, end of period	$ 2,669,700	$ 1,625,500