Maintenance Reserves and Accrued Maintenance Costs (1) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Accrued maintenance cost [Roll Forward]
Balance, beginning of period	$ 878,700	$ 1,013,400
Additions [Abstract]
Charged to expense	3,788,700	2,367,100
Capital equipment	384,800	64,800
Accrued claims related to refundable maintenance reserves	388,200	578,100
Prepaid maintenance and other	31,800	32,900
Total additions	4,593,500	3,042,900
Deductions [Abstract]
Payments	3,182,600	1,960,500
Other	558,200	479,800
Total deductions	3,740,800	2,440,300
Net increase in accrued maintenance costs	852,700	602,600
Balance, end of period	$ 1,731,400	$ 1,616,000