Adoption of New Accounting Standards (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Recognized a discrete tax benefit	$ 200,000	$ 1,800,000		$ 2,000,000
Tax benefit (expense) recognized as additional paid-in capital			$ 300,000		$ (100,000)
Reclassified tax benefits to operating activities				172,173,180	131,076,603
Cash flows from operating activities				$ 263,557,719	255,129,954
Additional Paid-in Capital [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax benefit (expense) recognized as additional paid-in capital			300,000		(100,000)
Tax benefit recognized as additional paid-in capital			800,000		1,000,000
Tax expense recognized as additional paid-in capital			$ 500,000		1,100,000
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified tax benefits to operating activities					1,700,000
Cash flows from operating activities					$ 1,700,000
Effect on earnings per share (in dollars per share)	$ 0.01			$ 0.01