Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ (1,130,836)	$ 11,313,015
Comprehensive Income	347,450,807	306,026,008	$ 277,942,231
Balance at end of period	(1,271,305)	(1,130,836)	11,313,015
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(44,909)	1,403,899	2,507,922
Other comprehensive income (loss) before reclassifications	(2,818,090)	(1,448,808)	(1,104,023)
Comprehensive Income	(2,818,090)	(1,448,808)	(1,104,023)
Balance at end of period	(2,862,999)	(44,909)	1,403,899
Unrealized gains(losses) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	829,907	10,868,322	19,467,441
Other comprehensive income (loss) before reclassifications	2,167,196	(5,513,842)	1,536,416
Amounts reclassified from accumulated other comprehensive income	(208,128)	(4,524,573)	(10,135,535)
Comprehensive Income	1,959,068	(10,038,415)	(8,599,119)
Balance at end of period	2,788,975	829,907	10,868,322
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(1,915,834)	(959,206)	0
Other comprehensive income (loss) before reclassifications	(672,419)	(1,659,115)	(959,206)
Amounts reclassified from accumulated other comprehensive income	1,390,972	702,487	0
Comprehensive Income	718,553	(956,628)	(959,206)
Balance at end of period	$ (1,197,281)	$ (1,915,834)	$ (959,206)