Annual report pursuant to Section 13 and 15(d)

Note 11 - Selected Quarterly Financial Data (Unaudited) (Details) - Unaudited Financial Data of the Trust for Each Quarter

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Note 11 - Selected Quarterly Financial Data (Unaudited) (Details) - Unaudited Financial Data of the Trust for Each Quarter (USD $)
3 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, 2013
Dec. 31, 2012
Dec. 31, 2011
Unaudited Financial Data of the Trust for Each Quarter [Abstract]                      
Income $ 12,503,683 $ 14,936,609 $ 9,953,933 $ 6,726,854 $ 7,276,793 $ 7,043,281 $ 8,706,738 $ 9,580,079 $ 44,109,074 $ 32,587,456 $ 34,300,508
Income before income taxes 11,145,275 14,103,915 9,049,678 5,843,710 6,218,508 6,369,983 7,956,109 8,778,286 40,142,578 29,322,886 30,755,918
Net income $ 7,519,106 $ 9,431,118 $ 6,130,440 $ 4,137,844 $ 4,113,797 $ 4,311,092 $ 5,284,674 $ 5,938,255 $ 27,218,508 $ 19,647,818 $ 20,594,769
Net income per Sub-share Certificate (in Dollars per share) $ 0.88 $ 1.10 $ 0.71 $ 0.47 $ 0.47 $ 0.48 $ 0.59 $ 0.65 $ 3.16 $ 2.20 $ 2.21