Comprehensive Income (AOCI Rollforward) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 21,975,363	$ 17,570,711
Comprehensive Income	277,942,231	227,334,601	173,615,348
Balance at end of period	11,313,015	21,975,363	17,570,711
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	2,507,922	2,458,933	2,129,957
Other comprehensive income before reclassifications	(1,104,023)	48,989	328,976
Amounts reclassified from accumulated other comprehensive income	0	0	0
Comprehensive Income	(1,104,023)	48,989	328,976
Balance at end of period	1,403,899	2,507,922	2,458,933
Unrealized gains(losses) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	19,467,441	15,111,778	10,412,246
Other comprehensive income before reclassifications	1,536,416	16,139,845	10,138,902
Amounts reclassified from accumulated other comprehensive income	(10,135,535)	(11,784,182)	(5,439,370)
Comprehensive Income	(8,599,119)	4,355,663	4,699,532
Balance at end of period	10,868,322	19,467,441	15,111,778
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	0	0	0
Other comprehensive income before reclassifications	(959,206)	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	0
Comprehensive Income	(959,206)	0	0
Balance at end of period	$ (959,206)	$ 0	$ 0