Income Taxes (Schedule Of Deferred Income Tax Assets And Liabilities) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets:
Accruals not currently deductible	$ 4,546,767	$ 4,282,470
Stock based compensation	8,594,640	18,701,361
Other	3,679,680	3,924,945
Total deferred income tax assets	16,821,087	26,908,776
Liabilities:
Excess tax over book depreciation	(46,123,681)	(65,642,206)
Goodwill	(18,972,334)	(23,225,969)
Unrealized gain on investments	(2,093,105)	(1,435,322)
Intangible assets	(4,172,726)	(5,368,886)
Other	(4,347,885)	(2,449,012)
Net deferred income taxes	$ (58,888,644)	$ (71,212,620)