Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (8,434,543)	$ (15,651,274)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation expense	14,150	21,278
Loss on disposition of property and equipment	37,478	0
Stock-based compensation expense	1,124,970	2,217,709
Non-cash interest expense	194,898	0
Amortization of discount on marketable investment securities	(159,226)	(56,530)
Changes in operating assets and liabilities:
Accrued interest income	(6,825)	29,687
Prepaid and other current assets	(320,255)	(123,898)
Accounts payable	(358,148)	557,904
Litigation insurance recovery	3,319,927	0
Litigation settlement payable	(4,250,000)	0
Accrued expenses	(1,008,424)	600,061
Cash used in operating activities	(9,845,998)	(12,405,063)
Cash flows from investing activities:
Refund of rental deposit	7,000	0
Purchases of marketable investment securities	(20,698,650)	(24,746,690)
Maturities of marketable investment securities	27,038,944	29,682,000
Cash provided by investing activities	6,347,294	4,935,310
Cash flows from financing activities:
Proceeds from debt	10,000,000	0
Proceeds from stock option exercises	0	534,977
Net proceeds from common stock offering	90,761	10,644,883
Cash provided by financing activities	10,090,761	11,179,860
Net increase in cash, cash equivalents, and restricted cash	6,592,057	3,710,107
Cash, cash equivalents, and restricted cash at beginning of period	3,210,749	5,560,716
Cash, cash equivalents, and restricted cash at end of period	9,802,806	9,270,823
Supplemental disclosure of cash flow information:
Interest paid	427,639	0
Income taxes paid	700	700
Supplemental disclosure of non-cash investing and financing activity:
Net unrealized gain on available-for-sale securities	763	7,960
Accrued final payment charge on debt	$ 194,898	$ 0