Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (2,719,971)	$ (4,861,260)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation expense	5,261	7,093
Loss on disposition of property and equipment	37,478	0
Stock-based compensation expense	427,280	632,290
Non-cash interest expense	64,966	0
Amortization of discount on marketable investment securities	(48,863)	(6,169)
Changes in operating assets and liabilities:
Accrued interest income	(24,182)	2,997
Prepaid and other current assets	160,248	67,509
Accounts payable	(209,714)	607,595
Litigation insurance recovery	(246,722)	0
Accrued expenses	(1,191,992)	411,194
Cash used in operating activities	(3,746,211)	(3,138,751)
Cash flows from investing activities:
Refund of rental deposit	7,000	0
Purchases of marketable investment securities	(13,210,225)	(6,972,103)
Maturities of marketable investment securities	12,300,000	8,400,000
Cash provided by (used in) investing activities	(903,225)	1,427,897
Cash flows from financing activities:
Proceeds from debt agreement	10,000,000	0
Proceeds from stock option exercises	0	388,551
Net proceeds from common stock offering	0	2,698,098
Cash provided by financing activities	10,000,000	3,086,649
Net increase in cash and cash equivalents	5,350,564	1,375,795
Cash and cash equivalents at beginning of period	3,210,749	5,560,716
Cash and cash equivalents at end of period	8,561,313	6,936,511
Supplemental disclosure of cash flow information:
Income taxes paid	700	700
Supplemental disclosure of non-cash investing and financing activity:
Net unrealized gain (loss) on available-for-sale securities	(15,035)	2,707
Accrued final payment charge on debt	$ 64,966	$ 0