Income Taxes (Schedule Of Deferred Income Tax Assets And Liabilities) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Assets:
Accruals not currently deductible	$ 4,282,470	$ 4,157,660
Stock based compensation	18,701,361	20,360,105
Other	3,924,945	3,928,824
Total deferred income tax assets	26,908,776	28,446,589
Liabilities:
Excess tax over book depreciation	(65,642,206)	(53,538,861)
Goodwill	(23,225,969)	(16,047,068)
Unrealized gain on investments	(1,435,322)	(961,980)
Intangible assets	(5,368,886)	(3,056,712)
Other	(2,449,012)	(2,114,430)
Net deferred income taxes	$ (71,212,619)	$ (47,272,462)