CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net loss	$ (13,930,593)	$ (10,988,558)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	31,916	18,558
Stock-based compensation	1,224,647	1,459,855
Realized loss from marketable securities	137,248	201,827
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(687,497)	(61,394)
Accounts payable	(420,948)	962,450
Accrued expenses	(739,261)	(796,010)
Deferred revenue	49,315,631	0
Security deposits	13,766	(7,121)
Net cash provided by (used in) operating activities	34,944,909	(9,210,393)
Cash flows from investing activities
Purchases of fixed assets	0	(2,163)
Purchases of marketable securities	0	(7,951,257)
Redemptions of marketable securities	6,658,000	10,451,332
Net cash provided by investing activities	6,658,000	2,497,912
Cash flows from financing activities
Proceeds from exercise of stock options	640,017	0
Net cash provided by financing activities	640,017	0
Net increase (decrease) in cash and cash equivalents	42,242,926	(6,712,481)
Cash and cash equivalents at the beginning of the period	28,575,085	27,107,526
Cash and cash equivalents at the end of the period	70,818,011	20,395,045
Supplemental disclosure of cash flow information:
Change in unrealized gain on marketable securities available-for-sale	$ 76,092	$ 72,090