Summary of Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Cash and cash equivalents:
Cash Equivalents, at Amorized Cost	$ 153,994,922
Cash Equivalents, Unrealized (Losses) Gains	0
Cash Equivalents, at Fair Value	153,994,922
Short-term investments:
Available-for-sale Securities, Short-term Investments, Amortized Cost	66,812,014
Cash And Cash Equivalents And Short Term Investments Amortized Cost	220,806,936
Available-for-sale Securities, Gross Unrealized Gain	(1,052)
Short-term Investments	66,810,962	$ 0
Short term investment Unrealized (Losses) Gains	(1,052)
Cash, Cash Equivalents, and Short-term Investments	220,805,884
Cash And Money Market Funds [Member]
Cash and cash equivalents:
Cash Equivalents, at Amorized Cost	12,125,898
Cash Equivalents, Unrealized (Losses) Gains	0
Cash Equivalents, at Fair Value	12,125,898
US Government Corporations and Agencies Securities [Member]
Cash and cash equivalents:
Cash Equivalents, at Amorized Cost	141,869,024
Cash Equivalents, Unrealized (Losses) Gains	0
Cash Equivalents, at Fair Value	141,869,024
Short-term investments:
Available-for-sale Securities, Short-term Investments, Amortized Cost	46,793,691
Available-for-sale Securities, Gross Unrealized Gain	221
Short-term Investments	46,793,912
US Treasury Securities [Member]
Short-term investments:
Available-for-sale Securities, Short-term Investments, Amortized Cost	20,018,323
Available-for-sale Securities, Gross Unrealized Gain	(1,273)
Short-term Investments	$ 20,017,050