Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 11,313,015	$ 21,975,363
Comprehensive Income	306,026,008	277,942,231	$ 227,334,601
Balance at end of period	(1,130,836)	11,313,015	21,975,363
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	1,403,899	2,507,922	2,458,933
Other comprehensive income before reclassifications	(1,448,808)	(1,104,023)	48,989
Amounts reclassified from accumulated other comprehensive income	0	0	0
Comprehensive Income	(1,448,808)	(1,104,023)	48,989
Balance at end of period	(44,909)	1,403,899	2,507,922
Unrealized gains(losses) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	10,868,322	19,467,441	15,111,778
Other comprehensive income before reclassifications	(5,513,842)	1,536,416	16,139,845
Amounts reclassified from accumulated other comprehensive income	(4,524,573)	(10,135,535)	(11,784,182)
Comprehensive Income	(10,038,415)	(8,599,119)	4,355,663
Balance at end of period	829,907	10,868,322	19,467,441
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(959,206)	0	0
Other comprehensive income before reclassifications	(1,659,115)	(959,206)	0
Amounts reclassified from accumulated other comprehensive income	702,487	0	0
Comprehensive Income	(956,628)	(959,206)	0
Balance at end of period	$ (1,915,834)	$ (959,206)	$ 0