Opus Genetics (IRD) S-4 6 Jul 20 Registration of securities issued in business combination transactions Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2020
Document And Entity Information [Abstract]
Document Type	S-4
Entity Registrant Name	REXAHN PHARMACEUTICALS, INC.
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Amendment Flag	false
Entity Central Index Key	0001228627

Balance Sheet

Balance Sheet - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 10,998,096	$ 9,219,547	$ 8,744,301
Marketable securities		2,997,220	5,981,520
Prepaid expenses and other current assets	290,756	447,206	1,173,847
Total Current Assets	11,288,852	12,663,973	15,899,668
Security Deposits	25,681	25,681	30,785
Operating Lease Right-of-Use Assets	171,870	203,348
Equipment, Net	66,515	75,770	112,473
Total Assets	11,552,918	12,968,772	16,042,926
Current Liabilities:
Accounts payable and accrued expenses	1,237,007	1,265,731	3,152,550
Deferred revenue	600,000	1,500,000
Operating lease liabilities, current	144,610	139,765
Total Current Liabilities	1,981,617	2,905,496	3,152,550
Operating Lease Liabilities, non-current	25,790	63,605
Warrant Liabilities	100,109	41,717	2,307,586
Other Liabilities			19,900
Total Liabilities	2,107,516	3,010,818	5,480,036
Commitments and Contingencies
Stockholders' Equity:
Preferred stock
Common stock	402	402	312
Additional paid-in capital	173,354,446	173,278,144	165,267,656
Accumulated other comprehensive income (loss)		2,084	(17,836)
Accumulated deficit	(163,909,446)	(163,322,676)	(154,687,242)
Total Stockholders' Equity	9,445,402	9,957,954	10,562,890
Total Liabilities and Stockholders' Equity	$ 11,552,918	$ 12,968,772	$ 16,042,926

Balance Sheet (Parenthetical)

Balance Sheet (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet [Abstract]
Preferred Stock, Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred Stock, Shares Authorized	10,000,000	10,000,000	10,000,000
Preferred Stock, Shares Issued	0	0	0
Preferred Stock, Shares Outstanding	0	0	0
Common Stock, Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Common Stock, Shares Authorized	75,000,000	75,000,000	75,000,000
Common Stock, Shares, Issued	4,019,141	4,019,141	3,122,843
Common Stock, Shares, Outstanding	4,019,141	4,019,141	3,122,843

Statement Of Operations

Statement Of Operations - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Statement Of Operations [Abstract]
Revenues:	$ 1,150,000
Expenses:
General and administrative	1,256,006	$ 1,695,523	5,738,227	7,428,615
Research and development	456,790	2,242,229	5,476,776	13,109,058
Total Expenses	1,712,796	3,937,752	11,215,003	20,537,673
Loss from Operations	(562,796)	(3,937,752)	(11,215,003)	(20,537,673)
Other Income
Interest income	34,418	81,385	313,700	254,344
Other income				368,750
Unrealized (loss) gain on fair value of warrants	(58,392)	1,513,371	2,265,869	5,546,049
Total Other (Loss) Income	(23,974)	1,594,756	2,579,569	6,169,143
Net Loss Before Provision for Income Taxes	(586,770)	(2,342,996)	(8,635,434)	(14,368,530)
Provision for Income Taxes
Net Loss	$ (586,770)	$ (2,342,996)	$ (8,635,434)	$ (14,368,530)
Net loss per share, basic and diluted	$ (0.15)	$ (0.62)	$ (2.18)	$ (5.25)
Weighted average number of shares outstanding, basic and diluted	4,019,141	3,779,953	3,960,163	2,738,506

Statement Of Comprehensive Loss

Statement Of Comprehensive Loss - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Statement Of Comprehensive Loss [Abstract]
Net Loss	$ (586,770)	$ (2,342,996)	$ (8,635,434)	$ (14,368,530)
Unrealized (loss) gain on available-for-sale securities	(2,084)	5,234	19,920	39,050
Comprehensive Loss	$ (588,854)	$ (2,337,762)	$ (8,615,514)	$ (14,329,480)

Statement Of Stockholders' Equi

Statement Of Stockholders' Equity - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2017	$ 264	$ 157,143,930	$ (140,318,712)	$ (56,886)	$ 16,768,596
Balance, shares at Dec. 31, 2017	2,639,319
Issuance of common stock and units, net of issuance costs	$ 48	6,872,741			6,872,789
Issuance of common stock and units, net of issuance costs, Shares	480,770
Common stock issued in exchange for services		22,650			22,650
Common stock issued in exchange for services, shares	1,250
Common stock issued from vested restricted stock units, shares	1,504
Stock-based compensation		1,228,335			1,228,335
Net Loss			(14,368,530)		(14,368,530)
Other Comprehensive income (loss)				39,050	39,050
Balance at Dec. 31, 2018	$ 312	165,267,656	(154,687,242)	(17,836)	$ 10,562,890
Balance, shares at Dec. 31, 2018	3,122,843				3,122,843
Issuance of common stock and units, net of issuance costs	$ 90	7,553,738			$ 7,553,828
Issuance of common stock and units, net of issuance costs, Shares	895,834
Common stock issued in exchange for services, shares	464
Stock-based compensation		161,000			161,000
Net Loss			(2,342,996)		(2,342,996)
Other Comprehensive income (loss)				5,234	5,234
Balance at Mar. 31, 2019	$ 402	172,982,394	(157,030,238)	(12,602)	15,939,956
Balance, shares at Mar. 31, 2019	4,019,141
Balance at Dec. 31, 2018	$ 312	165,267,656	(154,687,242)	(17,836)	$ 10,562,890
Balance, shares at Dec. 31, 2018	3,122,843				3,122,843
Issuance of common stock and units, net of issuance costs	$ 90	7,553,738			$ 7,553,828
Issuance of common stock and units, net of issuance costs, Shares	895,834
Common stock issued from vested restricted stock units, shares	464
Stock-based compensation		456,750			456,750
Net Loss			(8,635,434)		(8,635,434)
Other Comprehensive income (loss)				19,920	19,920
Balance at Dec. 31, 2019	$ 402	173,278,144	(163,322,676)	2,084	$ 9,957,954
Balance, shares at Dec. 31, 2019	4,019,141				4,019,141
Stock-based compensation		76,302			$ 76,302
Net Loss			(586,770)		(586,770)
Other Comprehensive income (loss)				$ (2,084)	(2,084)
Balance at Mar. 31, 2020	$ 402	$ 173,354,446	$ (163,909,446)		$ 9,445,402
Balance, shares at Mar. 31, 2020	4,019,141				4,019,141

Statement Of Cash Flows

Statement Of Cash Flows - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities:
Net loss	$ (586,770)	$ (2,342,996)	$ (8,635,434)	$ (14,368,530)
Adjustments to reconcile net loss to net cash used in operating activities:
Compensatory stock				22,650
Depreciation and amortization	9,255	11,533	40,992	48,211
Loss on sale of equipment		9,594	9,594
Amortization of premiums and discounts on marketable securities, net	(4,864)	(18,499)	(108,214)	39,251
Stock-based compensation	76,302	161,000	456,750	1,228,335
Amortization and termination of deferred research and development arrangement				(375,000)
Unrealized loss (gain) on fair value of warrants	58,392	(1,513,371)	(2,265,869)	(5,546,049)
Changes in assets and liabilities:
Prepaid expenses and other assets	156,450	73,367	608,143	230,694
Accounts payable and accrued expenses	(28,724)	(906,350)	(1,886,819)	(81,376)
Deferred revenue	(900,000)	150,000	1,500,000
Other, net	(1,492)	(4,373)	3,724	(36,824)
Net Cash Used in Operating Activities	(1,221,451)	(4,380,095)	(10,277,133)	(18,838,638)
Cash Flows from Investing Activities:
Purchase of equipment		(13,181)	(19,383)	(39,224)
Sale of equipment		5,500	5,500
Purchase of marketable securities		(8,887,566)	(8,887,566)
Redemption of marketable securities	3,000,000	3,000,000	12,000,000	11,950,220
Net Cash Provided by (Used in) Investing Activities	3,000,000	(5,895,247)	3,098,551	11,910,996
Cash Flows from Financing Activities:
Issuance of common stock and units, net of issuance costs		7,653,828	7,653,828	6,872,789
Payment of deferred offering costs				(100,000)
Net Cash Provided by Financing Activities		7,653,828	7,653,828	6,772,789
Net Increase (Decrease) in Cash and Cash Equivalents	1,778,549	(2,621,514)	475,246	(154,853)
Cash and Cash Equivalents - beginning of period	9,219,547	8,744,301	8,744,301	8,899,154
Cash and Cash Equivalents - end of period	10,998,096	6,122,787	9,219,547	8,744,301
Supplemental Cash Flow Information
Operating cash flows paid for amounts included in the measurement of lease liabilities	$ 38,262	84,651	197,224
Non-cash financing and investing activties:
Warrants issued		4,735,913	4,735,913	$ 4,841,830
Operating lease right-of-use assets obtained in exchange for lease obligations:		$ 380,935	$ 380,935

Operations And Organization

Operations And Organization	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Operations And Organization [Abstract]
Operations And Organization	1. Operations and Organization Operations Rexahn Pharmaceuticals, Inc. (the “Company”), a Delaware corporation, is a biopharmaceutical company whose principal operations are the development of innovative treatments for cancer. The Company had an accumulated deficit of $163,909,446 at March 31, 2020 and anticipates incurring losses in the foreseeable future. In September 2019, the Company commenced a process to explore and evaluate strategic alternatives to enhance shareholder value and engaged a financial advisory firm to assist in the process.  The Company believes that its cash and cash equivalents of approximately $11.0 million as of March 31, 2020 will be sufficient to cover its cash flow requirements for its current activities for at least the next 12 months from the date these financial statements were issued.  Basis of Presentation The accompanying unaudited condensed financial statements of the Company have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete financial statements. In the opinion of the Company’s management, all adjustments (consisting of only normal recurring accruals) considered necessary for a fair presentation of the Company’s financial position as of March 31, 2020 and December 31, 2019 and of the results of operations, comprehensive loss, stockholders’ equity and cash flows for the three months ended March 31, 2020 and 2019 have been included. Operating results for the three months ended March 31, 2020 are not necessarily indicative of results that may be expected for any other interim period or the full fiscal year ending December 31, 2020. The accompanying unaudited condensed financial statements should be read in conjunction with the audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 (the “2019 Form 10-K”). Information included in the condensed balance sheet as of December 31, 2019 has been derived from the Company’s audited financial statements for the year ended December 31, 2019 included in the 2019 Form 10-K. The unaudited condensed financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business.  Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Actual results may ultimately differ from these estimates. These estimates are reviewed periodically, and as adjustments become necessary, they are reported in earnings in the period in which they become available. COVID-19 Pandemic The outbreak of the COVID-19 disease, which the World Health Organization declared a pandemic in March 2020, has led to disruption in the global economy and the biopharmaceutical industry. The extent of the COVID-19 pandemic’s impact on the Company’s business, financial condition and results of operations, as well as the Company’s ability to enter into and complete a strategic transaction, is highly uncertain and will depend on various factors, including the duration and scope of the pandemic, restrictions on business and social distancing guidelines that may be requested or mandated by governmental authorities, other actions taken to contain the impact of the pandemic, and impacts on the Company’s ability or the ability of potential strategic partners to access the markets on favorable terms, or at all. 	1. Operations and Organization Rexahn Pharmaceuticals, Inc. (the “Company”), a Delaware corporation, is a biopharmaceutical company whose principal operations are the development of innovative treatments for cancer. The Company had an accumulated deficit of $ 163,322,676 at December 31, 2019 and anticipates incurring losses in the foreseeable future. In September 2019, the Company commenced a process to explore and evaluate strategic alternatives to enhance shareholder value and engaged a financial advisory firm to assist in the process.  The Company believes that its cash, cash equivalents and marketable securities of approximately $12.2 million as of December 31, 2019 will be sufficient to cover its cash flow requirements for its current activities for at least the next 12 months from the date these financial statements were issued. 

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates  The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Actual results may ultimately differ from these estimates. These estimates are reviewed periodically and as adjustments become necessary, they are reported in earnings in the period in which they become available. Cash and Cash Equivalents Cash and cash equivalents include cash on hand and short ‑term investments purchased with remaining maturities of three months or less at acquisition. Marketable Securities Marketable securities are considered “available-for-sale” in accordance with Financial Statement Accounting Board (“FASB”) Accounting Standards Codification (“ASC”) 320, “Debt and Equity Securities,” and thus are reported at fair value in the Company’s accompanying balance sheet, with unrealized gains and losses excluded from earnings and reported as a separate component of stockholders’ equity. Amounts reclassified out of accumulated other comprehensive loss into realized gains and losses are accounted for on the basis of specific identification and are included in other income or expense in the statement of operations. The Company classifies such investments as current on the balance sheet as the investments are readily marketable and available for use in the Company’s current operations. Equipment Equipment is stated at cost less accumulated depreciation. Depreciation, based on the lesser of the term of the lease or the estimated useful life of the assets, is provided as follows:    Life Depreciation Method  Furniture and fixtures 7 years straight line  Office equipment 5 years straight line  Laboratory equipment 5 -7 years straight line  Computer equipment 3 -5 years straight line  Leasehold improvements 3 -5 years straight line  Fair Value of Financial Instruments The carrying amounts reported in the accompanying financial statements for cash and cash equivalents and accounts payable and accrued expenses approximate fair value because of the short ‑term maturity of these financial instruments. The fair value of warrant liabilities is discussed in Note 12, and the fair value of marketable securities and certain other assets and liabilities is discussed in Note 16. Warrants The Company classifies its stock warrants as either liability or equity instruments in accordance with ASC 480, “Distinguishing Liabilities from Equity” (ASC 480), depending on the specific terms of the warrant agreement. Warrants that the Company may be required to redeem through payment of cash or other assets outside its control are classified as liabilities pursuant to ASC 480 and are initially and subsequently measured at their estimated fair values. Stock warrants are also classified as warrant liabilities in accordance with ASC 815, “Derivatives and Hedging” (ASC 815) if the warrant contains terms that could require “net cash settlement” and therefore, do not meet the conditions necessary for equity classification according to ASC 815. Warrant instruments that could require “net cash settlement” in the absence of express language precluding such settlement are initially classified as warrant liabilities at their estimated fair values, regardless of the likelihood that such instruments will ever be settled in cash. The Company will continue to record liability-classified warrants at fair value until the warrants are exercised, expire or are amended in a way that would no longer require these warrants to be classified as a liability. For additional discussion on warrants, see Note 12. Research and Development Research and development costs are expensed as incurred. Research and development expenses consist primarily of third-party service costs under research and development agreements, salaries and related personnel costs, including stock-based compensation, costs to acquire pharmaceutical products and product rights for development and amounts paid to contract research organizations, hospitals and laboratories for the provision of services and materials for drug development and clinical trials. Costs incurred in obtaining the licensing rights to technology in the research and development stage that have no alternative future uses and are for unapproved product compounds are expensed as incurred. Income Taxes The Company accounts for income taxes in accordance with ASC 740, “Income Taxes”. Deferred tax assets and liabilities are recorded for differences between the financial statement and tax basis of the assets and liabilities that will result in taxable or deductible amounts in the future based on enacted tax laws and rates. ASC 740 requires that a valuation allowance be established when it is more likely than not that all portions of a deferred tax asset will not be realized. A review of all positive and negative evidence needs to be considered, including a company’s current and past performance, the market environment in which the company operates, length of carryback and carryforward periods and existing contracts that will result in future profits. Income tax expense is recorded for the amount of income tax payable or refundable for the period, increased or decreased by the change in deferred tax assets and liabilities during the period. As a result of the Company’s significant cumulative losses, the Company determined that it was appropriate to establish a valuation allowance for the full amount of net deferred tax assets. The calculation of the Company’s tax liabilities involves the inherent uncertainty associated with the application of complex tax laws. The Company is subject to examination by various taxing authorities. The Company believes that, as a result of its loss carryforward sustained to date, any examination would result in a reduction of its net operating losses rather than a tax liability. As such, the Company has not provided for any additional taxes that would be estimated under ASC 740. Stock-Based Compensation In accordance with ASC 718, “Stock Compensation,” compensation costs related to share-based payment transactions, including employee stock options, are to be recognized in the financial statements. In addition, the Company adheres to the guidance set forth within U.S. Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin (“SAB”) No. 107, which provides the Staff’s views regarding the interaction between ASC 718 and certain SEC rules and regulations, and provides interpretations with respect to the valuation of share-based payments for public companies. For additional discussion on stock-based compensation, see Note 11. Concentration of Credit Risk ASC 825, “Financial Instruments,” requires disclosure of any significant off balance sheet risk and credit risk concentration. The Company does not have significant off ‑balance sheet risk or credit concentration. The Company maintains cash and cash equivalents with major financial institutions. From time to time the Company has funds on deposit with commercial banks that exceed federally insured limits. The balances are insured by the Federal Deposit Insurance Corporation up to $250,000. At December 31, 2019, the Company’s uninsured cash balance was $ 8,969,547 . Management does not consider this to be a significant credit risk as the banks are large, established financial institutions. Reclassification Certain amounts in the prior year’s financial statements have been reclassified to conform to the current year presentation with no material impact on the financial statements. Recent Accounting Pronouncements Affecting the Company Leases  In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous U.S. GAAP. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company adopted the standard on January 1, 2019. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allows carryforward of the historical lease classification. The Company did not elect the hindsight practical expedient. The Company made an accounting policy election to keep leases with an initial term of 12 months or less off the balance sheet. The Company recognizes those lease payments in the consolidated statements of operations on a straight-line basis over the lease term.  Adoption of this standard resulted in recognition of additional net right-of-use assets and lease liabilities, both of which were not quantitatively material to the Company’s financial statements, and there was no impact to the Company’s accumulated deficit. Adoption of this standard did not have a notable impact on the Company’s liquidity.  See Note 8 for additional discussion on the Company’s leases and the adoption of ASU 2016-02.      

Marketable Securities

Marketable Securities	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities [Abstract]
Marketable Securities	2. Marketable Securities  Marketable securities are considered “available-for-sale” in accordance with Financial Accounting Standards Board Accounting Standards Codification (“ASC”) 320, “Debt and Equity Securities,” and thus are reported at fair value in the Company’s accompanying balance sheet, with unrealized gains and losses excluded from earnings and reported as a separate component of stockholders’ equity. Amounts reclassified out of accumulated other comprehensive income (loss) into realized gains and losses are accounted for on the basis of specific identification and are included in other income or expense in the statement of operations. The Company classifies such investments as current on the balance sheet as the investments are readily marketable and available for use in current operations.  The Company had no marketable securities as of March 31, 2020. The following table shows the Company’s marketable securities’ adjusted cost, gross unrealized gains and losses, and fair value by significant investment category as of December 31, 2019:    December 31, 2019   Cost Gross Unrealized Gross Unrealized Fair  Basis Gains Losses Value  Commercial Paper $ 1,996,216 $ 1,184 $ - $ 1,997,400  Corporate Bonds 998,920 900 - 999,820  Total Marketable Securities $ 2,995,136 $ 2,084 $ - $ 2,997,220 	3. Marketable Securities The following table shows the Company’s marketable securities’ adjusted cost, gross unrealized gains and losses, and fair value by significant investment category as of December 31, 2019 and 2018:     December 31, 2019  Cost Gross Unrealized Gross Unrealized Fair  Basis Gains Losses Value  Commercial Paper $ 1,996,216 $ 1,184 $ - $ 1,997,400  Corporate Bonds 998,920 900 - 999,820  Total Marketable Securities $ 2,995,136 $ 2,084 $ - $ 2,997,220   December 31, 2018  Cost Gross Unrealized Gross Unrealized Fair  Basis Gains Losses Value  Corporate Bonds $ 5,999,356 $ - $ (17,836) $ 5,981,520  The Company typically invests in highly rated securities, with the primary objective of minimizing the potential risk of principal loss. As of December 31, 2019, all of the Company’s marketable securities are due to mature in less than one year.

Prepaid Expenses And Other Curr

Prepaid Expenses And Other Current Assets	12 Months Ended
	Dec. 31, 2019
Prepaid Expenses And Other Current Assets [Abstract]
Prepaid Expenses And Other Current Assets	4. Prepaid Expenses and Other Current Assets    December 31, December 31,  2019 2018   Deposits on contracts $ - $ 618,417  Prepaid expenses and other current assets 447,206 555,430   $ 447,206 $ 1,173,847 Deposits on contracts consist of deposits on research and development contracts for services that had not been incurred as of the balance sheet date. Prepaid expenses and other assets include prepaid general and administrative expenses not yet incurred as of the balance sheet date.

Equipment, Net

Equipment, Net	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Equipment, Net [Abstract]
Equipment, Net	3. Equipment, Net    March 31, December 31,  2020 2019   Furniture and fixtures $ 67,650 $ 67,650  Office and computer equipment 163,440 163,440  Leasehold improvements 116,403 116,403   Total equipment 347,493 347,493  Less: Accumulated depreciation and amortization (280,978) (271,723)   Net carrying amount $ 66,515 $ 75,770 	5. Equipment, Net    December 31, December 31,  2019 2018   Furniture and fixtures $ 67,650 $ 82,686  Office and computer equipment 163,440 159,489  Laboratory equipment - 447,653  Leasehold improvements 116,403 131,762   Total equipment 347,493 821,590  Less: Accumulated depreciation and amortization (271,723) (709,117)   Net carrying amount $ 75,770 $ 112,473 During the year ended December 31, 2019, the Company sold its laboratory equipment prior to terminating its laboratory lease. The Company recorded a loss of $9,594 on the sale, which is included in general and administrative expense in the Company’s statement of operations.

Accounts Payable And Accrued Ex

Accounts Payable And Accrued Expenses	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Accounts Payable And Accrued Expenses [Abstract]
Accounts Payable And Accrued Expenses	4. Accounts Payable and Accrued Expenses     March 31, December 31,  2020 2019   Trade payables $ 891,419 $ 488,285  Accrued expenses 165,931 471,700  Accrued research and development contract costs 125,992 221,170  Payroll liabilities 53,665 84,576   $ 1,237,007 $ 1,265,731 	6. Accounts Payable and Accrued Expenses     December 31, December 31,  2019 2018   Trade payables $ 488,285 $ 547,519  Accrued expenses 471,700 140,637  Accrued research and development contract costs 221,170 1,782,131  Payroll liabilities 84,576 682,263   $ 1,265,731 $ 3,152,550 

Collaboration and License Agree

Collaboration and License Agreements	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Collaboration and License Agreements [Abstract]
Collaboration and License Agreements	5. License Agreements  BioSense Global LLC On March 10, 2020, the Company entered into an amendment to its collaboration and license agreement, (as amended, the “License and Assignment Agreement”) with BioSense Global LLC (“BioSense”) to advance the development and commercialization of RX-3117 for all human uses in the Republic of Singapore, China, Hong Kong, Macau, and Taiwan (the “Territory”). Under the terms of the License and Assignment Agreement, upon payment in full of an upfront payment, the Company will (i) grant BioSense an exclusive license to develop and commercialize pharmaceutical products containing RX-3117 as a single agent for all human uses in the Territory and (ii) assign and transfer all of the Company’s patents and patent applications related to RX-3117 in the Territory. The upfront payment consists of an aggregate of $1,650,000 , of which $1,500,000 has been received to date. Under the License and Assignment Agreement, the Company is eligible to receive milestone payments in an aggregate of up to $84.5 million upon the achievement of development, regulatory and commercial goals and will also be eligible to receive tiered royalties in the mid-single digits to low tens on annual net sales in the Territory. The Company has evaluated the License and Assignment Agreement under ASC 606, “Revenue from Contracts with Customers,” to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations under the License and Assignment Agreement. The Company identified the exclusive license to develop RX-3117 and the supply of RX-3117 drug product, drug substance and intermediate materials (collectively, the “Transferred Materials”) as the distinct performance obligations in the contract. The Company has determined that it will recognize revenue related to the exclusive license to develop RX-3117 and the supply of the Transferred Materials transfers to BioSense at a point in time when the exclusive license is conveyed and the Transferred Materials are made available for delivery to BioSense, respectively. The Company has determined the transaction price contains both fixed and variable consideration. The fixed consideration is equal to the upfront payment of $1,650,000. The variable consideration relates to the milestone payments and future sales-based royalty payments. The Company estimates the variable consideration in the contract using the most likely amount method. The Company determined at the contract outset and as of March 31, 2020 that all milestone payments should be fully constrained, as it is not probable that a significant reversal of revenue will not occur in a future period, given the significance of the milestone payments and that the payments are earned based upon the achievement of events that are highly susceptible to factors outside of the Company’s control. Future sales-based royalties related to the exclusive license to develop RX-3117 will be recognized in the period the underlying sales transaction occurs. The $1,650,000 upfront payment has been allocated to the performance obligations on the basis of the relative standalone selling price estimated for each performance obligation. The Company has determined the standalone selling price of the exclusive license to develop RX-3117 using the adjusted market approach, which represents the price the market will bear based on the license rights granted and the state of the intellectual property, and has determined the standalone selling price of the supply of the Transferred Materials using a cost approach. Accordingly, the Company has allocated $750,000 of the upfront transaction price to the exclusive license to develop RX-3117 and $900,000 to the supply of the Transferred Materials. Additional transaction price recognized in future periods related to milestone payments and royalties will be allocated solely to the exclusive license to develop RX-3117, as these amounts relate to efforts associated with the development and commercialization of products related to the exclusive license to develop RX-3117. As of March 31, 2020, $1,500,000 of the upfront payment had been paid, and the remaining $150,000 remained unpaid. As of March 31, 2020, the Company had satisfied the performance obligation related to the Transferred Materials and therefore recognized $900,000 in revenue which was previously classified as deferred revenue. As of March 31, 2020, the exclusive license had not been transferred and no revenue was recognized related to that performance obligation. Therefore, the Company has recorded the additional $600,000 of transaction consideration received as of March 31, 2020 as deferred revenue on the Company’s balance sheet. Zhejiang HaiChang Biotechnology Co., Ltd. On February 8, 2020, the Company entered into an exclusive license agreement (the “HaiChang License Agreement”) with Zhejiang HaiChang Biotechnology Co., Ltd. (“HaiChang”) pursuant to which the Company granted HaiChang an exclusive (even as to the Company), royalty-bearing, sublicensable worldwide license to research, develop and commercialize pharmaceutical products comprising RX-0201 (subject to and limited by the exclusive rights of NEXT BT Co. Ltd (“Next BT”) with respect to RX-0201 in Asia), the nano-liposomal formulation of RX-0201 known as RX-0301, and RX-0047, a proprietary compound currently in preclinical development. HaiChang has agreed to use commercially reasonable efforts to develop, seek regulatory approval for, and commercialize one product comprising RX-0301 and one product comprising RX-0047.  HaiChang paid a one-time upfront payment of $250,000 to the Company for certain materials to be transferred by the Company to HaiChang. HaiChang will pay the Company development milestone payments in an aggregate of up to $63,000,000 with respect to RX-0201 and RX-0301 and up to $33,000,000 with respect to RX-0047, and royalties based on percentages of net sales in the low tens with respect to RX-0201 and RX-0301 and the mid-single digits with respect to RX-0047. However, if HaiChang exclusively sublicenses its rights to a third party with respect to RX-0201 and RX-0301 or RX-0047 in a particular jurisdiction, instead of the foregoing milestones and royalties to the extent relating to such compound(s) and jurisdiction, HaiChang will pay the Company a percentage of any sublicensing revenue received by HaiChang, provided that in any event HaiChang will pay a milestone payment on initiation of a Phase 3 clinical trial that is subject to reduction by the amount of any sublicensing revenue paid with respect to the applicable compound(s) as of the time of initiation of the trial.  The Company accounts for the HaiChang License Agreement under ASC 606. The Company has determined the performance obligations under the contract relates to the transfer of materials and the license of intellectual property. Revenue associated with the materials and license are recognized at a point in time. The Company has determined the transaction price contains both fixed and variable consideration. The fixed consideration is equal to the upfront payment of $250,000 . At the outset of the contract, the value of the license was determined to be de minimis given the early stage of clinical development of the intellectual property, and allocated the entire fixed consideration to the materials. The Company transferred the materials during the three months ended March 31, 2020 and therefore recognized the entire fixed consideration as revenue. The variable consideration relates to the milestone payments, sublicense fees and future sales-based royalty payments . The Company estimates variable consideration under the contract using the expected value method. Given the early stage and the uncertain success of the development work to be performed by HaiChang, the Company has determined that the variable consideration in the contract should be fully constrained at the contract outset and as of March 31, 2020.	 7. Collaboration and License Agreements BioSense Global LLC On February 25, 2019, the Company entered into a collaboration and license agreement (as amended, the “Collaboration and License Agreement”) with BioSense Global LLC (“BioSense”) to advance the development and commercialization of RX-3117 for pancreatic and other cancers in the Republic of Singapore, China, Hong Kong, Macau, and Taiwan (the “Territory”). Under the terms of the Collaboration and License Agreement, the Company will grant BioSense an exclusive license to develop and commercialize pharmaceutical products containing RX-3117 as a single agent for the prevention or treatment of metastatic pancreatic cancer and other forms of cancer in the Territory that is effective upon payment in full of an upfront payment. The upfront payment consists of an aggregate of $3,000,000 . Under the Collaboration and License Agreement, the Company is also eligible to receive milestone payments (i) in an aggregate of up to $126,000,000 for the achievement of development and regulatory goals in China and (ii) in an aggregate of up to $100,000,000 for the achievement of annual sales goals in the Territory with respect to each pharmaceutical product containing RX-3117 as a single agent. The Company will also be eligible to receive tiered royalties in the low double digits to mid-teens on annual net sales in the Territory. The Company has evaluated the Collaboration and License Agreement under ASC 606, “Revenue from Contracts with Customers,” to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations under the Collaboration and License Agreement. The Company identified the exclusive license to develop RX-3117 and the supply of RX-3117 clinical material for clinical trials as the distinct performance obligations in the contract. The Company has determined that it will recognize revenue related to the exclusive license to develop RX-3117 and the supply of RX-3117 clinical material transfers to BioSense at a point in time when the exclusive license is conveyed and RX-3117 clinical material is delivered to BioSense, respectively. The Company has determined the transaction price contains both fixed and variable consideration. The fixed consideration is equal to the upfront payment of $3,000,000 . The variable consideration relates to the milestone payments and future sales-based royalty payments. The Company estimates the variable consideration in the contract using the most likely amount method. The Company determined at the contract outset and as of December 31, 2019 that all milestone payments should be fully constrained, as it is not probable that a significant reversal of revenue will not occur in a future period, given the significance of the milestone payments and that the payments are earned based upon the achievement of events that are highly susceptible to factors outside of the Company’s control. Future sales-based royalties related to the exclusive license to develop RX-3117 will be recognized in the period the underlying sales transaction occurs. The $3,000,000 upfront payment has been allocated to the performance obligations on the basis of the relative standalone selling price estimated for each performance obligation. The Company has determined the standalone selling price of the exclusive license to develop RX-3117 using the adjusted market approach, which represents the price the market will bear based on the license rights granted and the state of the intellectual property, and has determined the standalone selling price of the supply of RX-3117 clinical material using a cost plus a margin approach. Accordingly, the Company has allocated $2,500,000 of the upfront transaction price to the exclusive license to develop RX-3117 and $500,000 to the supply of RX-3117 clinical material. Additional transaction price recognized in future periods related to milestone payments and royalties will be allocated solely to the exclusive license to develop RX-3117, as these amounts relate to efforts associated with the development and commercialization of products related to the exclusive license to develop RX-3117. As of December 31, 2019, $1,500,000 of the upfront payment had been paid, and the remaining $1,500,000 which was due on September 23, 2019 remained unpaid. The Company has not terminated the Collaboration and License Agreement nor amended its performance obligations. As neither performance obligation has been satisfied as of December 31, 2019, no revenue has been recognized for the year ended December 31, 2019. The Company has recorded the $1,500,000 of transaction consideration received as of December 31, 2019 as deferred revenue on the Company’s balance sheet. Zhejiang HaiChang Biotechnology Co., Ltd. On February 8, 2018, the Company entered into a research and development collaboration agreement with Zhejiang HaiChang Biotechnology Co., Ltd. (“HaiChang”) under which HaiChang agreed to develop RX-0301, a nano-liposomal formulation of RX-0201, using its proprietary QTsome™ technology and to conduct certain preclinical and clinical activities through completion of a Phase 2a proof-of-concept clinical trial in hepatocellular carcinoma in China.  The Company accounts for this contract under ASC 606. The Company has determined the sole performance obligation under the contract with HaiChang relates to the license of intellectual property in exchange for variable, non-cash consideration in the form of the rights to the enhanced intellectual property developed by HaiChang under the contract. Revenue associated with this license is recognized at a point in time. At the outset of the contract, the value of the license was determined to be de minimis given the early stage of clinical development of the intellectual property. Because the consideration in the contract varies based upon the success of the research and development efforts of HaiChang, the Company has determined that the non-cash consideration in the contract represents variable consideration. The Company estimates variable consideration under the contract using the expected value method. Given the early stage and the uncertain success of the development work to be performed by HaiChang, as of December 31, 2019 and 2018, the Company has determined that the variable consideration in the contract should be fully constrained at the contract outset and as of December 31, 2019 and 2018. The Company has not recorded revenue for this contract for the years ended December 31, 2019 and 2018.  As further described in Note 16, on February 8, 2020, the Company entered into an exclusive license with HaiChang (the “HaiChang License Agreement”). In connection with entering into the HaiChang License Agreement, the parties terminated the research and development collaboration agreement with HaiChang. Rexgene Biotech Co., Ltd. In 2003, the Company entered into a collaborative research agreement with Rexgene Biotech Co., Ltd. (“Rexgene”), which agreed to assist the Company with the research, development and clinical trials necessary for registration of the Company’s product candidate RX-0201 in Asia. In accordance with the agreement, Rexgene paid the Company a one-time fee of $ 1, 500,000 in 2003. The agreement provided that it would expire upon the later of (i) 20 years after the date of the agreement or (ii) the expiration of the patents relating to RX-0201. The amortization reduces research and development expenses for the periods presented. The payment from Rexgene was used in the cooperative funding of the costs of development of RX-0201. On February 5, 2018, the Company and NEXT BT Co. Ltd. (“Next BT”), the successor in interest to Rexgene, terminated the agreement. In exchange for Next BT terminating its rights to RX-0201 in Asia, the Company agreed to pay Next BT a royalty in the low single digits of any net sales of RX-0201 the Company makes in Asia and 50% of the Company’s licensing revenue related to the licensing of RX-0201 in Asia, up to an aggregate of $5,000,000 . Upon termination of the agreement, the unamortized deferred research and development arrangement liability of $368,750 under the agreement was eliminated and recognized as other income. The Company historically used 20 years as its basis for recognition and accordingly research and development expenses were reduced by $6,250 for the period beginning January 1, 2018 up to the agreement’s termination.  Merck Sharp & Dohme B.V. On August 16, 2018, the Company entered into a clinical trial collaboration and supply agreement (the “Collaboration Agreement”) with Merck Sharp & Dohme B.V. (“Merck”) to conduct a Phase 2 clinical trial to evaluate the safety and efficacy of the combination of RX-5902 with Merck’s anti-PD ‑1 therapy, KEYTRUDA (pembrolizumab), in patients with metastatic triple negative breast cancer (TNBC). Under the terms of the Collaboration Agreement, the Company will sponsor the clinical trial and Merck will supply the Company with KEYTRUDA for use in the trial at no cost to the Company. The Collaboration Agreement provides that the Company and Merck will jointly own clinical data generated from the clinical trial. The Company is currently evaluating the development strategy for RX-5902 and may or may not proceed with this trial.

Leases

Leases	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Leases	6. Leases  The Company leases 5,466 square feet of office space in Rockville, Maryland, with a lease term ending June 30, 2024. Under the lease agreement, the Company pays its allocable portion of real estate taxes and common area operating charges, which are recorded as variable lease costs. The lease has escalating rent payments for which the Company records lease expense on a straight-line basis over the lease term, and an option to terminate the leased premises, without penalty, on June 30, 2021. The Company is reasonably certain that it will not remain in these leased premises after the optional termination date, and therefore, is using the optional termination date in assessing the lease term.  The following table summarizes the right of use lease assets and lease liabilities as of March 31, 2020:     Right-of-Use Assets $ 171,870  Operating Lease Liabilities  Current $ 144,610  Long Term 25,790  Total Operating Lease Liabilities $ 170,400  The components of lease expense were as follows:    For the Three Months Ended March 31,  2020 2019  Operating lease cost $ 36,771 $ 80,279  Variable lease cost 5,693 16,012   Total Lease Cost $ 42,464 $ 96,291  The right-of-use asset and lease liability were calculated using an estimated incremental borrowing rate of 11% . At March 31, 2020, the weighted average lease term was 1.3 years. The table below summarizes the Company’s scheduled future minimum lease payments recorded on the balance sheet, as of March 31, 2020:    Year Ending December 31:  2020 (excluding the three months ended March 31, 2020) $ 117,018  2021 65,364  Minimum lease payments 182,382  Less: Imputed interest (11,982)  Present value of minimum lease payments 170,400  Less: current maturities of lease obligations (144,610)  Long-term lease obligations $ 25,790 	8. Leases  The Company adopted ASU 2016-02 on January 1, 2019. Upon adoption, leases classified as operating leases under previous U.S. GAAP are recognized as right of use lease assets and lease liabilities. The classification criteria for distinguishing between finance leases and operating leases pursuant to ASU 2016-02 are substantially similar to the classification criteria for distinguishing between capital leases and operating leases in the previous leases guidance. Upon adoption, the Company did not have any finance leases, and the Company’s operating leases were as follows:  Office Space Lease  The Company leases 5,466 square feet of office space in Rockville, Maryland, with a lease term ending June 30, 2024. Prior to the amendment of this lease on March 18, 2019, the lease covered 7,193 square feet and had a lease term ending June 30, 2019. Under the lease agreement, the Company pays its allocable portion of real estate taxes and common area operating charges. The lease has escalating rent payments for which the Company records lease expense on a straight-line basis over the lease term, and an option to terminate the leased premises, without penalty, on June 30, 2021. The Company is reasonably certain that it will not remain in these leased premises after the optional termination date, and therefore, is using the optional termination date in assessing the lease term.  Laboratory Lease  The Company previously leased 2,552 square feet of laboratory space with a lease term due to end on June 30, 2020. The Company terminated its laboratory lease agreement on February 4, 2019 and surrendered the premises on February 28, 2019.  The following table summarizes the right of use lease assets and lease liabilities as of December 31, 2019:    Right-of-Use Assets $ 203,348   Operating Lease Liabilities  Current $ 139,765  Long Term 63,605  Total Operating Lease Liabilities $ 203,370  Lease expense for the year ended December 31, 2019 was $229,701 , which includes $200,948 in operating lease costs and $28,753 in variable lease costs. The right-of-use asset and lease liability were calculated using an estimated incremental borrowing rate of 11% . At December 31, 2019, the weighted average lease term was 1.5 years.   The table below summarizes the Company’s scheduled future minimum lease payments recorded on the balance sheet, as of December 31, 2019:     Year Ending December 31:  2020 $ 155,280  2021 65,364  Minimum lease payments 220,644  Less: Imputed interest (17,274)  Present value of minimum lease payments 203,370  Less: current maturities of lease obligations (139,765)  Long-term lease obligations $ 63,605

Net Loss Per Common Share

Net Loss Per Common Share	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Net Loss Per Common Share [Abstract]
Net Loss Per Common Share	7. Net Loss per Common Share Basic loss per common share is computed by dividing net loss by the weighted average number of shares of common stock outstanding for the period. Diluted loss per common share is computed by dividing net loss by the weighted average number of shares of common stock outstanding, plus the number of common share equivalents that would be dilutive. As of March 31, 2020 and December 31, 2019, there were stock options, restricted stock units, and warrants to acquire, in the aggregate, 2,070,511 and 2,126,063 shares of the Company’s common stock, respectively, that are potentially dilutive. However, diluted loss per share is the same as basic loss per share for all periods presented because the inclusion of common share equivalents would be anti-dilutive.	9. Net Loss per Common Share Basic loss per common share is computed by dividing net loss by the weighted average number of shares of common stock outstanding for the period. Diluted loss per common share is computed by dividing net loss by the weighted average number of shares of common stock outstanding, plus the number of common share equivalents that would be dilutive. As of December 31, 2019 and 2018, there were stock options, restricted stock units (“RSUs”) and warrants to acquire, in the aggregate, 2,126,063 and 1,322,602 shares of the Company’s common stock, respectively, that are potentially dilutive. However, diluted loss per share for all periods presented is the same as basic loss per share for those periods because the inclusion of common share equivalents would be anti-dilutive. 

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2019
Common Stock [Abstract]
Common Stock	10. Common Stock The following transactions occurred during the years ended December 31, 2019 and 2018:  Reverse Stock Split  On April 12, 2019 the Company effected a 1-for- 12 reverse stock split of the outstanding shares of the Company’s common stock. Each 12 shares of the Company’s common stock, par value $0.0001 per share, issued and outstanding at the effective time of the reverse stock split were reclassified and combined into one share of common stock par value $0.0001 per share. The number of shares of common stock and preferred stock the Company is authorized to issue remained unchanged at 75,000,000 and 10,000,000 , respectively. All share and per share amounts have been restated for all periods to give retroactive effect to the reverse stock split. Accordingly, an amount equal to the par value of the decreased shares resulting from the reverse stock split was reclassified from “Common stock” to “Additional paid-in capital.”  Authorized Shares On August 30, 2018, the Company’s stockholders approved an increase in the Company’s authorized shares of stock from 50,000,000 to 75,000,000 . Public Offerings October 2018 On October 19, 2018, the Company closed a registered direct offering of 480,770 shares of common stock and warrants to purchase up to 480,771 shares of common stock, resulting in gross proceeds to the Company of approximately $7,500,000 . The common stock and warrants were sold in units, consisting of a share of common stock and a warrant to purchase a share of common stock, at a price of $15.60 per unit, with an exercise price for the warrants of $20.04 per share . The warrants became exercisable April 19, 2019 and will remain exercisable through April 19, 2024. The Company also issued warrants to purchase up to 28,848 shares of the Company’s common stock, at an exercise price of $19.50 per share, to designees of the placement agent in the offering. The warrants issued to the investors and to the placement agent are classified as equity instruments. The closing costs of this offering of $896,117 included $286,906 for the placement agent warrants and $627,211 in placement agent and other fees that are recorded as a reduction of the gross proceeds of the offering. January 2019 On January 25, 2019, the Company closed an underwritten public offering of 895,834 shares of common stock and warrants to purchase up to 895,886 shares of common stock, resulting in gross proceeds to the Company of approximately $8,600,000 . The common stock and warrants were sold in units, consisting of a share of common stock and a warrant to purchase a share of common stock, at a price of $9.60 per unit, with an exercise price for the warrants of $9.60 per share . The warrants were immediately exercisable and will remain exercisable until January 25, 2024. The warrants issued are classified as equity instruments. The closing costs of this offering were $1,046,172 in underwriter’s and other professional fees that are recorded as a reduction in the gross proceeds of the offering. 

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Stock-Based Compensation [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation As of March 31, 2020, the Company had 149,022 options to purchase common stock outstanding. In June 2013, the Company’s shareholders voted to approve the Rexahn Pharmaceuticals, Inc. 2013 Stock Option Plan (the “2013 Plan”). Under the 2013 Plan, the Company grants equity awards to key employees, directors and consultants of the Company. The Company has reserved 283,333 shares of common stock for issuance pursuant to the 2013 Plan. As of March 31, 2020, there were 144,366 options outstanding under the 2013 Plan, and 136,936 shares were available for issuance. In addition, as of March 31, 2020, there were 4,656 options outstanding under a previously established stock option plan under which no new stock options may be granted. Accounting for Awards Stock-based compensation expense is the estimated fair value of options granted amortized on a straight-line basis over the requisite vesting service period for the entire portion of the award. Total stock-based compensation recognized by the Company for the three months ended March 31, 2020 and 2019 is as follows:    For the Three Months Ended March 31,  2020 2019 Statement of operations line item:  General and administrative $ 72,420 $ 116,679  Research and development 3,882 44,321   Total $ 76,302 $ 161,000  No income tax benefit has been recognized in the statement of operations for stock-based compensation arrangements as the Company has provided for a 100% valuation allowance on its deferred tax assets. Summary of Stock Option Transactions  A summary of stock option activity for the three months ended March 31, 2020 is as follows:     Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value  Outstanding, January 1, 2020 204,574 $ 35.60 7.3 years $ -  Granted - $ -  Exercised - $ -  Expired (2,498) $ 159.60  Cancelled (53,054) $ 60.40   Outstanding, March 31, 2020 149,022 $ 24.69 7.8 years $ -  Exercisable, March 31, 2020 75,304 $ 37.16 7.0 years $ -  A summary of the Company’s unvested options as of March 31, 2020 and changes during the three months ended March 31, 2020 is presented below:     2020  Number of Options Weighted Average Fair Value at Grant Date  Unvested at January 1, 2020 81,311 $ 7.90  Granted - $ -  Vested (7,593) $ 8.34  Cancelled - $ -   Unvested at March 31, 2020 73,718 $ 7.85 As of March 31, 2020, there was $501,655 of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted average vesting period of 1.7 years.	11. Stock-Based Compensation As of December 31, 2019, the Company had 204,574 options outstanding. The Company grants equity awards to key employees, directors and consultants of the Company under the Rexahn Pharmaceuticals, Inc. 2013 Stock Option Plan (the “2013 Plan”). The Company has reserved 283,333 shares of common stock for issuance pursuant to the 2013 Plan. As of December 31, 2019, there were 187,420 options outstanding under the 2013 Plan, and 93,882 shares were available for issuance. In addition, as of December 31, 2019, there were 17,154 options outstanding under a previously established stock option plan under which no new stock options may be granted. Accounting for Awards Stock-based compensation expense is the estimated fair value of options and RSUs granted amortized on a straight-line basis over the requisite vesting service period for the entire portion of the award. Total stock-based compensation recognized by the Company for the years ended December 31, 2019 and 2018 is as follows:    For the Year Ended December 31,  2019 2018  Statement of operations line item:  General and administrative $ 393,483 $ 883,855  Research and development 63,267 344,480   Total $ 456,750 $ 1,228,335  No income tax benefit has been recognized in the statement of operations for stock-based compensation arrangements as the Company has provided for a 100% valuation allowance on its net deferred tax assets. Summary of Stock Option Transactions There were 52,465 stock options granted at exercise prices ranging from $5.23 to $7.45 with an aggregate fair value of $220,540 during the year ended December 31, 2019. There were 123,587 stock options granted at exercise prices ranging from $13.08 to $27.48 , with an aggregate fair value of $1,540,866 , during the year ended December 31, 2018. For the majority of the grants to employees, the vesting period is 25% on the first anniversary of the grant date and, thereafter, one thirty-sixth of the remaining option vests in equal installments on the first business day of each month until fully vested. Options generally expire ten years from the date of grant. For grants to non-employee directors and consultants of the Company, the vesting period is between one and three years, subject to the fulfillment of certain conditions in the individual stock agreements, or 100% upon the occurrence of certain events specified in the individual stock agreements. The fair value of options at the date of grant was estimated using the Black-Scholes option pricing model. The Company took into consideration guidance under ASC 718 and SAB 107 when reviewing and updating assumptions. Significant assumptions are determined as follows: Expected Term . The expected term is estimated using the simplified method whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. Volatility . Volatility is based on the historical trading volatility of the Company’s stock on the date of grant for a period consistent with the expected term. Risk-Free Interest Rate . The risk-free interest rate is based on the zero-coupon U.S. Treasury instruments on the date of grant with a maturity date consistent with the expected term of the Company’s stock option grants. Expected Dividend . To date, the Company has not declared or paid any cash dividends and do not have any plans to do so in the future. Therefore, the Company used an expected dividend yield of zero. Forfeitures -The Company recognizes forfeitures as they occur.  The assumptions made in calculating the fair values of options are as follows:     For the Year Ended December 31,  2019 2018  Black-Scholes assumptions  Expected dividend yield 0 % 0 %  Expected volatility 74-75 % 69-73 %  Risk-free interest rate 1.9 -2.6 % 2.3 -2.9 %  Expected term (in years) 5.5 -6 years 5.5 -6 years  The following table summarizes share-based transactions:     Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value  Outstanding, January 1, 2019 255,922 $ 41.88 7.8 years $ -  Granted 52,465 $ 6.41  Exercised - $ -  Expired (2,080) $ 97.78  Cancelled (101,733) $ 34.99   Outstanding, December 31, 2019 204,574 $ 35.60 7.3 years $ -  Exercisable, December 31, 2019 123,263 $ 51.15 6.2 years $ -   There were no stock options exercised during the years ended December 31, 2019 and 2018. The weighted average fair value of options granted was $4.20 and $12.48 for the years ended December 31, 2019 and 2018, respectively. A summary of the Company’s unvested options as of December 31, 2019 and changes during the year ended December 31, 2019 is presented below:     2019  Number of Options Weighted Average Fair Value at Grant Date  Unvested at January 1, 2019 131,531 $ 13.19  Granted 52,465 $ 4.20  Vested (51,386) $ 14.12  Cancelled (51,299) $ 11.47   Unvested at December 31, 2019 81,311 $ 7.90 As of December 31, 2019, there was $577,976 of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted average vesting period of 2.0 years. Summary of Restricted Stock Unit Transactions The fair value of an RSU award is the closing price of the Company’s common stock on the date of grant. A summary of RSU activity for the year ended December 31, 2019 is as follows:    Number of RSUs Weighted Average Grant Date Fair Value  Outstanding, January 1, 2019 1,394 $ 22.08  Granted - $ -  Vested and Released (464) $ 22.08  Cancelled (930) $ 22.08   Outstanding, December 31, 2019 - $ - 

Warrants

Warrants	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Warrants [Abstract]
Warrants	9. Warrants The following table summarizes the Company’s outstanding warrants to purchase common stock as of March 31, 2020 and December 31, 2019:     Number of Warrants: Warrant Issuance March 31, 2020 December 31, 2019 Exercise Price Expiration Date Liability-classified Warrants  November 2015 Investors 104,168 104,168 $ 63.60 May 2021  November 2015 Placement Agent 279 279 $ 63.60 Nov. 2020  March 2016 Investors 50,651 50,651 $ 50.40 Sept. 2021  September 2016 Investors 67,084 67,084 $ 36.00 Mar. 2022  June 2017 Investors 126,264 126,264 $ 48.00 Dec. 2022  June 2017 Placement Agent 15,153 15,153 $ 49.50 June 2022  October 2017 Investors 136,058 136,058 $ 34.20 Apr. 2023  October 2017 Placement Agent 16,327 16,327 $ 36.72 Oct. 2022  Total liability classified warrants 515,984 515,984  Equity-classified Warrants  October 2018 Investors 480,771 480,771 $ 20.04 Apr. 2024  October 2018 Placement Agent 28,848 28,848 $ 19.50 Oct. 2023  January 2019 Investors 895,886 895,886 $ 9.60 Jan. 2024  Total equity-classified warrants 1,405,505 1,405,505   Total outstanding warrants 1,921,489 1,921,489  The following table summarizes the Company’s warrant activity for the three months ended March 31, 2020:      Number of Warrants  Liability-classified Equity- classified Total Weighted average exercise price  Balance, January 1, 2020 515,984 1,405,505 1,921,489 $ 22.10  Issued during the period - - - $ -  Exercised during the period - - - $ -  Expired during the period - - $ -   Balance, March 31, 2020 515,984 1,405,505 1,921,489 $ 22.10 At March 31, 2020, the weighted average remaining contractual life of the outstanding warrants was 3.4 years. The following table summarizes the fair value of the liability-classified warrants as of the respective balance sheet dates:    Fair Value as of: Warrant Issuance: March 31, 2020 December 31, 2019  November 2015 Investors $ 971 $ 55  November 2015 Placement Agent - -  March 2016 Investor 1,240 439  September 2016 Investors 14,639 3,196  June 2017 Investors 30,364 11,736  June 2017 Placement Agent 2,574 845  October 2017 Investors 46,178 23,772  October 2017 Placement Agent 4,143 1,674  Total: $ 100,109 $ 41,717  The assumptions used in calculating the fair values of the liability-classified warrants are as follows:     March 31, 2020 December 31, 2019  Trading market prices $ 1.80 $ 1.91  Estimated future volatility 100 % 102 %  Dividend - - Estimated future risk-free rate 0.20 - 0.41 % 1.57 -1.72 % Equivalent volatility 113-129 % 85-94 % Equivalent risk-free rate 0.13 -0.19 % 1.57 -1.59 %  Fundamental transaction likelihood 50 % 50 %  Fundamental transaction timing July 2020 April 2020  . Changes in the fair value of the warrant liabilities, carried at fair value, reported as “unrealized (loss) gain on fair value of warrants” in the statement of operations:     For the Three Months Ended March 31,  2020 2019  November 2015 Investors $ (916) $ 197,084  November 2015 Placement Agent - 380  March 2016 Investors (801) 114,799  September 2016 Investors (11,443) 217,869  June 2017 Investors (18,628) 388,391  June 2017 Placement Agent (1,729) 41,911  October 2017 Investors (22,406) 496,501  October 2017 Placement Agent (2,469) 56,436  Total: $ (58,392) $ 1,513,371 	12. Warrants The following table summarizes the Company’s outstanding warrants to purchase common stock as of December 31, 2019 and 2018    Number of Warrants:  Warrant Issuance December 31, 2019 December 31, 2018 Exercise Price Expiration Date  Liability-classified Warrants  January 2014 Investors - 39,683 $ 153.60 Jan. 2019  November 2015 Investors 104,168 104,168 $ 63.60 May 2021  November 2015 Placement Agent 279 279 $ 63.60 Nov. 2020  March 2016 Investors 50,651 50,651 $ 50.40 Sept. 2021  September 2016 Investors 67,084 67,084 $ 36.00 Mar. 2022  June 2017 Investors 126,264 126,264 $ 48.00 Dec. 2022  June 2017 Placement Agent 15,153 15,153 $ 49.50 June 2022  October 2017 Investors 136,058 136,058 $ 34.20 Apr. 2023  October 2017 Placement Agent 16,327 16,327 $ 36.72 Oct. 2022  Total liability classified warrants 515,984 555,667   Equity-classified Warrants  October 2018 Investors 480,771 480,771 $ 20.04 Apr. 2024  October 2018 Placement Agent 28,848 28,848 $ 19.50 Oct. 2023  January 2019 Investors 895,886 - $ 9.60 Jan. 2024  Total equity-classified warrants 1,405,505 509,619   Total outstanding warrants 1,921,489 1,065,286 The following table summarizes the Company’s warrant activity for the year ended December 31, 2019:    Number of Warrants  Liability-classified Equity- classified Total Weighted average exercise price  Balance, January 1, 2019 555,667 509,619 1,065,286 $ 37.52  Issued during the period - 895,886 895,886 $ 9.60  Exercised during the period - - - $ -  Expired during the period (39,683) - (39,683) $ 153.60   Balance, December 31, 2019 515,984 1,405,505 1,921,489 $ 22.10 At December 31, 2019, the weighted average remaining contractual life of the outstanding warrants was 3.7 years. Accounting for Liability-classified Warrants  The warrants issued to investors in the November 2015, March 2016 and September 2016 offerings contain a provision for net cash settlement in the event of a fundamental transaction (contractually defined to include a merger, sale of substantially all assets, tender offer or share exchange). The warrant holder would have the option to receive cash equal to the fair value of the remaining unexercised portion of the warrant. In addition, the warrants from these three and the June 2017 and October 2017 offerings contain a cashless exercise provision that is exercisable only in the event that a registration statement is not effective. That provision may not be operative if an effective registration statement is not available because an exemption under the U.S. securities laws may not be available to issue unregistered shares. As a result, net cash settlement may be required, and these warrants require liability classification.  ASC 820 provides requirements for disclosure of liabilities that are measured at fair value on a recurring basis in periods subsequent to the initial recognition. Fair values for warrants were determined using the Binomial Lattice (“Lattice”) valuation technique. The Lattice model provides for dynamic assumptions regarding volatility and risk-free interest rates within the total period to maturity. Accordingly, within the contractual term, the Company provided multiple date intervals over which multiple volatilities and risk-free interest rates were used. These intervals allow the Lattice model to project outcomes along specific paths that consider volatilities and risk-free rates that would be more likely in an early exercise scenario.  Significant assumptions are determined as follows: Trading market values —Published trading market values; Exercise price —Stated exercise price; Term —Remaining contractual term of the warrant; Volatility —Historical trading volatility for periods consistent with the remaining terms; and Risk-free rate —Yields on zero coupon government securities with remaining terms consistent with the remaining terms of the warrants.  Due to the fundamental transaction provision, which could provide for early redemption of the warrants, the model also considered the probability the Company would enter into a fundamental transaction during the remaining term of the warrant. Historically, the Company has considered the probability of a fundamental transaction occurring to be remote, however, in September 2019, the Company commenced a process to explore and evaluate strategic alternatives to enhance shareholder value, which could result in a fundamental transaction as defined by the warrant agreements. Therefore, the Company adjusted the likelihood and timing of its fundamental transaction assumptions when calculating the fair values of the liability-classified warrants as of December 31, 2019.  The significant unobservable inputs used in the fair value measurement of the warrants include management’s estimate of the probability that a fundamental transaction may occur in the future. Significant increases (decreases) in the probability of occurrence would result in a significantly higher (lower) fair value measurement.  The following table summarizes the fair value of the warrants as of the respective balance sheet dates:    Fair Value as of:  Warrant Issuance: December 31, 2019 December 31, 2018  November 2015 Investors $ 55 $ 234,918  November 2015 Placement Agent - 435  March 2016 Investor 439 160,099  September 2016 Investors 3,196 333,834  June 2017 Investors 11,736 623,324  June 2017 Placement Agent 845 65,149  October 2017 Investors 23,772 801,551  October 2017 Placement Agent 1,674 88,276  Total: $ 41,717 $ 2,307,586 The assumptions used in calculating the fair values of the warrants are as follows:      December 31, 2019 December 31, 2018  Trading market prices $ 1.91 $ 11.16  Estimated future volatility 102 % 105 %  Dividend - -  Estimated future risk-free rate 1.57 -1.72 % 2.35 -2.53 %  Equivalent volatility 85-94 % 99-104 %  Equivalent risk-free rate 1.57 -1.59 % 2.51 -2.55 %  Fundamental transaction likelihood 50 % 5 %  Fundamental transaction timing April 2020 End of warrant term   Changes in the fair value of the warrant liabilities, carried at fair value, as reported as “unrealized gain on fair value of warrants” in the statement of operations:     For the Year Ended December 31,  2019 2018  Expired Warrants $ - $ 64,307  November 2015 Investors 234,863 1,025,132  November 2015 Placement Agent 435 2,501  March 2016 Investors 159,660 537,455  September 2016 Investors 330,638 720,249  June 2017 Investors 611,588 1,358,540  June 2017 Placement Agent 64,304 156,442  October 2017 Investors 777,779 1,504,001  October 2017 Placement Agent 86,602 177,422  Total: $ 2,265,869 $ 5,546,049 

Income Taxes

Income Taxes	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Income Taxes [Abstract]
Income Taxes	10. Income Taxes No provision for federal and state income taxes was required for the three months ended March 31, 2020 and 2019 due to the Company’s operating losses and increased deferred tax asset valuation allowance. At March 31, 2020 and December 31, 2019, the Company had unused net operating loss carry-forwards of approximately $157,964,000 and $ 156,586 ,000 respectively, which portions of expire at various dates beginning in 2021. Some of this amount may be subject to annual limitations under certain provisions of the Internal Revenue Code related to “changes in ownership.” As of March 31, 2020 and December 31, 2019, the deferred tax assets related to the aforementioned carry-forwards have been fully offset by valuation allowances, because significant utilization of such amounts is not presently expected in the foreseeable future. Deferred tax assets and valuation allowances consist of:     March 31, December 31,  2020 2019   Net Operating Loss Carryforwards $ 44,230,000 $ 43,844,000  Stock Compensation Expense 551,000 1,191,000  Book Tax Differences on Assets and Liabilities 163,000 464,000  Valuation Allowance (44,944,000) (45,499,000)   Net Deferred Tax Assets $ - $ - The Company files income tax returns in the U.S. federal and Maryland state jurisdictions. Tax years for fiscal 2016 through 2019 are open and potentially subject to examination by the federal and Maryland state taxing authorities.	13. Income Taxes No provision for federal and state income taxes was required for the years ended December 31, 2019 and 2018 due to the Company’s operating losses and increased deferred tax asset valuation allowance. At December 31, 2019 and 2018, the Company had unused net operating loss carry-forwards of approximately $156,586,000 and $147,086,000 respectively, portions of which expire at various dates beginning in 2021 . Some of this amount may be subject to annual limitations under certain provisions of the Internal Revenue Code related to “changes in ownership.” As of December 31, 2019 and 2018, the deferred tax assets related to the aforementioned carry-forwards have been fully offset by valuation allowances, because significant utilization of such amounts is not presently expected in the foreseeable future. Deferred tax assets and valuation allowances consist of:     December 31, December 31,  2019 2018   Net Operating Loss Carryforwards $ 43,844,000 $ 41,184,000  Stock Compensation Expense 1,191,000 1,608,000  Book Tax Differences on Assets and Liabilities 464,000 195,000  Valuation Allowance (45,499,000) (42,987,000)   Net Deferred Tax Assets $ - $ - The Company files income tax returns in the U.S. federal and Maryland state jurisdictions. Tax years for fiscal 2016 through 2019 are open and potentially subject to examination by the federal and Maryland state taxing authorities.

Commitments And Contingencies

Commitments And Contingencies	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Commitments And Contingencies [Abstract]
Commitments And Contingencies	11. Commitments and Contingencies a) The Company has contracted with various vendors for services, with terms that require payments over the terms of the agreements, usually ranging from two to 36 months. The costs to be incurred are estimated and are subject to revision. As of March 31, 2020, the total estimated cost to complete these agreements was approximately $800,000 . All of these agreements may be terminated by either party upon appropriate notice as stipulated in the respective agreements. b) On June 22, 2009, the Company entered into a License Agreement with Korea Research Institute of Chemical Technology (“KRICT”) to acquire the rights to all intellectual property related to quinoxaline-piperazine derivatives that were synthesized under a Joint Research Agreement. The agreement with KRICT calls for a one-time milestone payment of $1,000,000 within 30 days after the first achievement of marketing approval of the first commercial product arising out of or in connection with the use of KRICT’s intellectual property. As of March 31, 2020, the milestone has not occurred. c) The Company has established a 401(k) plan for its employees. The Company has elected to match 100% of the first 3% of an employee’s compensation plus 50% of an additional 2% of the employee’s deferral. Expense related to this matching contribution aggregated to $11,229 and $27,879 for the three months ended March 31, 2020 and 2019, respectively. d) On February 5, 2018, the Company and Next BT terminated a research collaboration agreement between the Company and Rexgene Biotech Co., Ltd, a predecessor in interest to Next BT. The Company agreed to pay Next BT a royalty in the low single digits of any net sales of RX-0201 the Company makes in Asia and 50% of the Company’s licensing revenue related to licensing of RX-0201 in Asia, up to an aggregate of $5,000,000 . As of March 31, 2020, the Company has not made any royalty payments to Next BT.	 14. Commitments and Contingencies a) The Company has contracted with various vendors for research and development services, with terms that require payments over the term of the agreements, usually ranging from two to 36 months. The costs to be incurred are estimated and are subject to revision. As of December 31, 2019, the total estimated cost to complete these agreements was approximately $ 1,750,000 . All of these agreements may be terminated by either party upon appropriate notice as stipulated in the respective agreements. b) On June 22, 2009, the Company entered into a License Agreement with Korea Research Institute of Chemical Technology (“KRICT”) to acquire the rights to all intellectual property related to quinoxaline-piperazine derivatives that were synthesized under a Joint Research Agreement. The agreement with KRICT calls for a one-time milestone payment of $ 1,000,000 within 30 days after the first achievement of marketing approval of the first commercial product arising out of or in connection with the use of KRICT’s intellectual property. As of December 31, 2019, the milestone has not occurred. c) The Company has established a 401(k) plan for its employees. The Company has elected to match 100% of the first 3% of an employee’s compensation plus 50% of an additional 2% of the employee’s deferral. Expense related to this matching contribution aggregated to $71,568 and $120,558 , for the years ended December 31, 2019 and 2018 respectively. d) On February 5, 2018, the Company and Next BT terminated the research collaboration agreement between the Company and Rexgene. In exchange for Next BT terminating its rights to RX-0201 in Asia, the Company agreed to pay Next BT a royalty in the low single digits of any net sales of RX-0201 the Company makes in Asia and 50% of the Company’s licensing revenue related to licensing of RX-0201 in Asia, up to an aggregate of $5,000,000 . As of December 31, 2019, the Company has not made any royalty payments to Next BT. 

Fair Value Measurements

Fair Value Measurements	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Fair Value Measurements [Abstract]
Fair Value Measurements	12. Fair Value Measurements ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date, not adjusted for transaction costs. ASC 820 also establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels giving the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3).  The three levels are described below:  Level 1 Inputs — Unadjusted quoted prices in active markets for identical assets or liabilities that are accessible by the Company; Level 2 Inputs — Quoted prices in markets that are not active or financial instruments for which all significant inputs are observable, either directly or indirectly; Level 3 Inputs — Unobservable inputs for the asset or liability including significant assumptions of the Company and other market participants.  The following tables present assets and liabilities that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy. de   Fair Value Measurements at March 31, 2020  Total Level 1 Level 2 Level 3 Liabilities:  Warrant Liabilities $ 100,109 $ - $ - $ 100,109    Fair Value Measurements at December 31, 2019  Total Level 1 Level 2 Level 3 Assets:  Commercial Paper $ 1,997,400 $ - $ 1,997,400 $ -  Corporate Bonds 999,820 - 999,820 -  Total Assets: $ 2,997,220 $ - $ 2,997,220 $ -  Liabilities:  Warrant Liabilities $ 41,717 $ - $ - $ 41,717  There have been no changes in the methodologies used at March 31, 2020 and December 31, 2019, and no transfers between Level 1, 2 and 3 during the three months ended March 31, 2020.  The reconciliation of changes to the fair value of the Company’s warrant liabilities for the three months ended March 31, 2020 is as follows:     Warrant Liabilities  Balance at January 1, 2020 $ 41,717  Unrealized losses, net 58,392  Balance at March 31, 2020 $ 100,109 	15. Fair Value Measurements ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date, not adjusted for transaction costs. ASC 820 also establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels giving the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3).  The three levels are described below:  Level 1 Inputs — Unadjusted quoted prices in active markets for identical assets or liabilities that are accessible by the Company; Level 2 Inputs — Quoted prices in markets that are not active or financial instruments for which all significant inputs are observable, either directly or indirectly; Level 3 Inputs — Unobservable inputs for the asset or liability including significant assumptions of the Company and other market participants. The following tables present assets and liabilities that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy.     Fair Value Measurements at December 31, 2019  Total Level 1 Level 2 Level 3  Assets:  Commercial Paper $ 1,997,400 $ - $ 1,997,400 $ -  Corporate Bonds 999,820 - 999,820 -  Total Assets: $ 2,997,220 $ - $ 2,997,220 $ -   Liabilities:  Warrant Liabilities $ 41,717 $ - $ - $ 41,717     Fair Value Measurements at December 31, 2018  Total Level 1 Level 2 Level 3  Assets:  Corporate Bonds $ 5,981,520 $ - $ 5,981,520 $ -   Liabilities:  Warrant Liabilities $ 2,307,586 $ - $ - $ 2,307,586  The fair value of the Company’s Level 2 marketable securities is determined by using quoted prices from independent pricing services that use market data for comparable securities in active or inactive markets. A variety of data inputs, including benchmark yields, interest rates, known historical trades and broker dealer quotes are used with pricing models to determine the quoted prices.  The fair value methodology for the warrant liabilities is disclosed in Note 12.  The carrying amounts reported in the financial statements for cash and cash equivalents (Level 1), and accounts payable and accrued expenses approximate fair value because of the short-term maturity of these financial instruments.  There have been no changes in the methodologies used at December 31, 2019 and 2018 and no transfers between Level 1, 2 and 3 during the years ended December 31, 2019 and 2018.  The following table sets forth a reconciliation of changes in the years ended December 31, 2019 and 2018 in the fair value of the liabilities classified as Level 3 in the fair value hierarchy:     Warrant Liabilities  Balance at January 1, 2019 $ 2,307,586  Unrealized gains, net (2,265,869)  Balance at December 31, 2019 $ 41,717    Warrant Liabilities  Balance at January 1, 2018 $ 7,853,635  Unrealized gains, net (5,546,049)  Balance at December 31, 2018 $ 2,307,586

Subsequent Event

Subsequent Event	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Subsequent Event [Abstract]
Subsequent Event	13. Subsequent Event  On April 7 , 2020, the Company notified Merck Sharp & Dohme B.V. (“Merck”) that it was terminating the Clinical Trial Collaboration and Supply Agreement dated as of August 16, 2018, by and between the Company and Merck, effective immediately, in connection with the Company’s determination to discontinue development of RX-5902 for the treatment of metastatic triple negative breast cancer. 	16. Subsequent Event  Exclusive License Agreement with HaiChang  On February 8, 2020, the Company entered into the HaiChang License Agreement pursuant to which the Company granted HaiChang an exclusive (even as to the Company), royalty-bearing, sublicensable worldwide license to research, develop and commercialize pharmaceutical products comprising RX-0201 (subject to and limited by the exclusive rights of Next BT with respect to RX-0201 in Asia), the nano-liposomal formulation of RX-0201 known as RX-0301, and RX-0047, a proprietary compound currently in preclinical development. HaiChang has agreed to use commercially reasonable efforts to develop, seek regulatory approval for, and commercialize one product comprising or RX-0301 and one product comprising RX-0047.  HaiChang will pay to the Company a one-time upfront payment in the amount of $250,000 for certain materials to be transferred by the Company to HaiChang. HaiChang will pay the Company development milestone payments in an aggregate of up to $63,000,000 with respect to RX-0201 and RX-0301 and up to $33,000,000 with respect to RX-0047, and royalties based on percentages of net sales in the low tens with respect to RX-0201 and RX-0301 and the mid-single digits with respect to RX-0047. However, if HaiChang exclusively sublicenses its rights to a third party with respect to RX-0201 and RX-0301 or RX-0047 in a particular jurisdiction, instead of the foregoing milestones and royalties to the extent relating to such compound(s) and jurisdiction, HaiChang will pay the Company a percentage of any sublicensing revenue received by HaiChang, provided that in any event HaiChang will pay a milestone payment on initiation of a Phase 3 clinical trial that is subject to reduction by the amount of any sublicensing revenue paid with respect to the applicable compound(s) as of the time of initiation of the trial.  In connection with entering into the HaiChang License Agreement, the parties terminated the previous research collaboration and license agreement with HaiChang. 

Operations And Organization (Po

Operations And Organization (Policies)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Operations And Organization [Abstract]
Operations	Operations Rexahn Pharmaceuticals, Inc. (the “Company”), a Delaware corporation, is a biopharmaceutical company whose principal operations are the development of innovative treatments for cancer. The Company had an accumulated deficit of $163,909,446 at March 31, 2020 and anticipates incurring losses in the foreseeable future. In September 2019, the Company commenced a process to explore and evaluate strategic alternatives to enhance shareholder value and engaged a financial advisory firm to assist in the process.  The Company believes that its cash and cash equivalents of approximately $11.0 million as of March 31, 2020 will be sufficient to cover its cash flow requirements for its current activities for at least the next 12 months from the date these financial statements were issued.
Basis Of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements of the Company have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete financial statements. In the opinion of the Company’s management, all adjustments (consisting of only normal recurring accruals) considered necessary for a fair presentation of the Company’s financial position as of March 31, 2020 and December 31, 2019 and of the results of operations, comprehensive loss, stockholders’ equity and cash flows for the three months ended March 31, 2020 and 2019 have been included. Operating results for the three months ended March 31, 2020 are not necessarily indicative of results that may be expected for any other interim period or the full fiscal year ending December 31, 2020. The accompanying unaudited condensed financial statements should be read in conjunction with the audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 (the “2019 Form 10-K”). Information included in the condensed balance sheet as of December 31, 2019 has been derived from the Company’s audited financial statements for the year ended December 31, 2019 included in the 2019 Form 10-K. The unaudited condensed financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Actual results may ultimately differ from these estimates. These estimates are reviewed periodically, and as adjustments become necessary, they are reported in earnings in the period in which they become available.	Use of Estimates  The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Actual results may ultimately differ from these estimates. These estimates are reviewed periodically and as adjustments become necessary, they are reported in earnings in the period in which they become available.
Reclassification		Reclassification Certain amounts in the prior year’s financial statements have been reclassified to conform to the current year presentation with no material impact on the financial statements.
COVID-19 Pandemic	COVID-19 Pandemic The outbreak of the COVID-19 disease, which the World Health Organization declared a pandemic in March 2020, has led to disruption in the global economy and the biopharmaceutical industry. The extent of the COVID-19 pandemic’s impact on the Company’s business, financial condition and results of operations, as well as the Company’s ability to enter into and complete a strategic transaction, is highly uncertain and will depend on various factors, including the duration and scope of the pandemic, restrictions on business and social distancing guidelines that may be requested or mandated by governmental authorities, other actions taken to contain the impact of the pandemic, and impacts on the Company’s ability or the ability of potential strategic partners to access the markets on favorable terms, or at all.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Actual results may ultimately differ from these estimates. These estimates are reviewed periodically, and as adjustments become necessary, they are reported in earnings in the period in which they become available.	Use of Estimates  The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Actual results may ultimately differ from these estimates. These estimates are reviewed periodically and as adjustments become necessary, they are reported in earnings in the period in which they become available.
Cash and Cash Equivalents		Cash and Cash Equivalents Cash and cash equivalents include cash on hand and short ‑term investments purchased with remaining maturities of three months or less at acquisition.
Marketable Securities		Marketable Securities Marketable securities are considered “available-for-sale” in accordance with Financial Statement Accounting Board (“FASB”) Accounting Standards Codification (“ASC”) 320, “Debt and Equity Securities,” and thus are reported at fair value in the Company’s accompanying balance sheet, with unrealized gains and losses excluded from earnings and reported as a separate component of stockholders’ equity. Amounts reclassified out of accumulated other comprehensive loss into realized gains and losses are accounted for on the basis of specific identification and are included in other income or expense in the statement of operations. The Company classifies such investments as current on the balance sheet as the investments are readily marketable and available for use in the Company’s current operations.
Equipment		Equipment Equipment is stated at cost less accumulated depreciation. Depreciation, based on the lesser of the term of the lease or the estimated useful life of the assets, is provided as follows:    Life Depreciation Method  Furniture and fixtures 7 years straight line  Office equipment 5 years straight line  Laboratory equipment 5 -7 years straight line  Computer equipment 3 -5 years straight line  Leasehold improvements 3 -5 years straight line 
Fair Value of Financial Instruments		Fair Value of Financial Instruments The carrying amounts reported in the accompanying financial statements for cash and cash equivalents and accounts payable and accrued expenses approximate fair value because of the short ‑term maturity of these financial instruments. The fair value of warrant liabilities is discussed in Note 12, and the fair value of marketable securities and certain other assets and liabilities is discussed in Note 16.
Warrants		Warrants The Company classifies its stock warrants as either liability or equity instruments in accordance with ASC 480, “Distinguishing Liabilities from Equity” (ASC 480), depending on the specific terms of the warrant agreement. Warrants that the Company may be required to redeem through payment of cash or other assets outside its control are classified as liabilities pursuant to ASC 480 and are initially and subsequently measured at their estimated fair values. Stock warrants are also classified as warrant liabilities in accordance with ASC 815, “Derivatives and Hedging” (ASC 815) if the warrant contains terms that could require “net cash settlement” and therefore, do not meet the conditions necessary for equity classification according to ASC 815. Warrant instruments that could require “net cash settlement” in the absence of express language precluding such settlement are initially classified as warrant liabilities at their estimated fair values, regardless of the likelihood that such instruments will ever be settled in cash. The Company will continue to record liability-classified warrants at fair value until the warrants are exercised, expire or are amended in a way that would no longer require these warrants to be classified as a liability. For additional discussion on warrants, see Note 12.
Research and Development		Research and Development Research and development costs are expensed as incurred. Research and development expenses consist primarily of third-party service costs under research and development agreements, salaries and related personnel costs, including stock-based compensation, costs to acquire pharmaceutical products and product rights for development and amounts paid to contract research organizations, hospitals and laboratories for the provision of services and materials for drug development and clinical trials. Costs incurred in obtaining the licensing rights to technology in the research and development stage that have no alternative future uses and are for unapproved product compounds are expensed as incurred.
Income Taxes		Income Taxes The Company accounts for income taxes in accordance with ASC 740, “Income Taxes”. Deferred tax assets and liabilities are recorded for differences between the financial statement and tax basis of the assets and liabilities that will result in taxable or deductible amounts in the future based on enacted tax laws and rates. ASC 740 requires that a valuation allowance be established when it is more likely than not that all portions of a deferred tax asset will not be realized. A review of all positive and negative evidence needs to be considered, including a company’s current and past performance, the market environment in which the company operates, length of carryback and carryforward periods and existing contracts that will result in future profits. Income tax expense is recorded for the amount of income tax payable or refundable for the period, increased or decreased by the change in deferred tax assets and liabilities during the period. As a result of the Company’s significant cumulative losses, the Company determined that it was appropriate to establish a valuation allowance for the full amount of net deferred tax assets. The calculation of the Company’s tax liabilities involves the inherent uncertainty associated with the application of complex tax laws. The Company is subject to examination by various taxing authorities. The Company believes that, as a result of its loss carryforward sustained to date, any examination would result in a reduction of its net operating losses rather than a tax liability. As such, the Company has not provided for any additional taxes that would be estimated under ASC 740.
Stock-Based Compensation		 Stock-Based Compensation In accordance with ASC 718, “Stock Compensation,” compensation costs related to share-based payment transactions, including employee stock options, are to be recognized in the financial statements. In addition, the Company adheres to the guidance set forth within U.S. Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin (“SAB”) No. 107, which provides the Staff’s views regarding the interaction between ASC 718 and certain SEC rules and regulations, and provides interpretations with respect to the valuation of share-based payments for public companies. For additional discussion on stock-based compensation, see Note 11.
Concentration of Credit Risk		Concentration of Credit Risk ASC 825, “Financial Instruments,” requires disclosure of any significant off balance sheet risk and credit risk concentration. The Company does not have significant off ‑balance sheet risk or credit concentration. The Company maintains cash and cash equivalents with major financial institutions. From time to time the Company has funds on deposit with commercial banks that exceed federally insured limits. The balances are insured by the Federal Deposit Insurance Corporation up to $250,000. At December 31, 2019, the Company’s uninsured cash balance was $8,969,547 . Management does not consider this to be a significant credit risk as the banks are large, established financial institutions.
Reclassification		Reclassification Certain amounts in the prior year’s financial statements have been reclassified to conform to the current year presentation with no material impact on the financial statements.
Recent Accounting Pronouncements Affecting the Company		Recent Accounting Pronouncements Affecting the Company Leases  In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous U.S. GAAP. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company adopted the standard on January 1, 2019. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allows carryforward of the historical lease classification. The Company did not elect the hindsight practical expedient. The Company made an accounting policy election to keep leases with an initial term of 12 months or less off the balance sheet. The Company recognizes those lease payments in the consolidated statements of operations on a straight-line basis over the lease term.  Adoption of this standard resulted in recognition of additional net right-of-use assets and lease liabilities, both of which were not quantitatively material to the Company’s financial statements, and there was no impact to the Company’s accumulated deficit. Adoption of this standard did not have a notable impact on the Company’s liquidity.  See Note 8 for additional discussion on the Company’s leases and the adoption of ASU 2016-02. 

Equipment, Net (Tables)

Equipment, Net (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Equipment, Net [Abstract]
Schedule Of Equipment, Net	  March 31, December 31,  2020 2019   Furniture and fixtures $ 67,650 $ 67,650  Office and computer equipment 163,440 163,440  Leasehold improvements 116,403 116,403   Total equipment 347,493 347,493  Less: Accumulated depreciation and amortization (280,978) (271,723)   Net carrying amount $ 66,515 $ 75,770 	  December 31, December 31,  2019 2018   Furniture and fixtures $ 67,650 $ 82,686  Office and computer equipment 163,440 159,489  Laboratory equipment - 447,653  Leasehold improvements 116,403 131,762   Total equipment 347,493 821,590  Less: Accumulated depreciation and amortization (271,723) (709,117)   Net carrying amount $ 75,770 $ 112,473 

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities [Abstract]
Schedule Of Cost And Fair Value Of Marketable Securities	  December 31, 2019   Cost Gross Unrealized Gross Unrealized Fair  Basis Gains Losses Value  Commercial Paper $ 1,996,216 $ 1,184 $ - $ 1,997,400  Corporate Bonds 998,920 900 - 999,820  Total Marketable Securities $ 2,995,136 $ 2,084 $ - $ 2,997,220 	  December 31, 2019  Cost Gross Unrealized Gross Unrealized Fair  Basis Gains Losses Value  Commercial Paper $ 1,996,216 $ 1,184 $ - $ 1,997,400  Corporate Bonds 998,920 900 - 999,820  Total Marketable Securities $ 2,995,136 $ 2,084 $ - $ 2,997,220   December 31, 2018  Cost Gross Unrealized Gross Unrealized Fair  Basis Gains Losses Value  Corporate Bonds $ 5,999,356 $ - $ (17,836) $ 5,981,520 

Prepaid Expenses And Other Cu_2

Prepaid Expenses And Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2019
Prepaid Expenses And Other Current Assets [Abstract]
Schedule Of Prepaid Expenses And Other Current Assets	  December 31, December 31,  2019 2018   Deposits on contracts $ - $ 618,417  Prepaid expenses and other current assets 447,206 555,430   $ 447,206 $ 1,173,847 

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Schedule Of Estimated Useful Lives	  Life Depreciation Method  Furniture and fixtures 7 years straight line  Office equipment 5 years straight line  Laboratory equipment 5 -7 years straight line  Computer equipment 3 -5 years straight line  Leasehold improvements 3 -5 years straight line 

Accounts Payable And Accrued _2

Accounts Payable And Accrued Expenses (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Accounts Payable And Accrued Expenses [Abstract]
Schedule Of Accounts Payable And Accrued Expenses	  March 31, December 31,  2020 2019   Trade payables $ 891,419 $ 488,285  Accrued expenses 165,931 471,700  Accrued research and development contract costs 125,992 221,170  Payroll liabilities 53,665 84,576   $ 1,237,007 $ 1,265,731 	  December 31, December 31,  2019 2018   Trade payables $ 488,285 $ 547,519  Accrued expenses 471,700 140,637  Accrued research and development contract costs 221,170 1,782,131  Payroll liabilities 84,576 682,263   $ 1,265,731 $ 3,152,550 

Leases (Tables)

Leases (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Summary Of Right Of Use Lease Assets And Lease Liabilities	  Right-of-Use Assets $ 171,870  Operating Lease Liabilities  Current $ 144,610  Long Term 25,790  Total Operating Lease Liabilities $ 170,400 	  Right-of-Use Assets $ 203,348   Operating Lease Liabilities  Current $ 139,765  Long Term 63,605  Total Operating Lease Liabilities $ 203,370 
Components Of Lease Expense	  For the Three Months Ended March 31,  2020 2019  Operating lease cost $ 36,771 $ 80,279  Variable lease cost 5,693 16,012   Total Lease Cost $ 42,464 $ 96,291 
Scheduled Future Minimum Lease Payments	 Year Ending December 31:  2020 (excluding the three months ended March 31, 2020) $ 117,018  2021 65,364  Minimum lease payments 182,382  Less: Imputed interest (11,982)  Present value of minimum lease payments 170,400  Less: current maturities of lease obligations (144,610)  Long-term lease obligations $ 25,790 	  Year Ending December 31:  2020 $ 155,280  2021 65,364  Minimum lease payments 220,644  Less: Imputed interest (17,274)  Present value of minimum lease payments 203,370  Less: current maturities of lease obligations (139,765)  Long-term lease obligations $ 63,605 

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Stock-Based Compensation [Abstract]
Summary Of Stock Compensation Expense	  For the Three Months Ended March 31,  2020 2019 Statement of operations line item:  General and administrative $ 72,420 $ 116,679  Research and development 3,882 44,321   Total $ 76,302 $ 161,000 	  For the Year Ended December 31,  2019 2018  Statement of operations line item:  General and administrative $ 393,483 $ 883,855  Research and development 63,267 344,480   Total $ 456,750 $ 1,228,335 
Schedule Of Assumptions Made In Calculating The Fair Value Of Options		   For the Year Ended December 31,  2019 2018  Black-Scholes assumptions  Expected dividend yield 0 % 0 %  Expected volatility 74-75 % 69-73 %  Risk-free interest rate 1.9 -2.6 % 2.3 -2.9 %  Expected term (in years) 5.5 -6 years 5.5 -6 years 
Summary Of Share-Based Transactions	   Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value  Outstanding, January 1, 2020 204,574 $ 35.60 7.3 years $ -  Granted - $ -  Exercised - $ -  Expired (2,498) $ 159.60  Cancelled (53,054) $ 60.40   Outstanding, March 31, 2020 149,022 $ 24.69 7.8 years $ -  Exercisable, March 31, 2020 75,304 $ 37.16 7.0 years $ - 	   Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value  Outstanding, January 1, 2019 255,922 $ 41.88 7.8 years $ -  Granted 52,465 $ 6.41  Exercised - $ -  Expired (2,080) $ 97.78  Cancelled (101,733) $ 34.99   Outstanding, December 31, 2019 204,574 $ 35.60 7.3 years $ -  Exercisable, December 31, 2019 123,263 $ 51.15 6.2 years $ - 
Summary Of Unvested Shares	   2020  Number of Options Weighted Average Fair Value at Grant Date  Unvested at January 1, 2020 81,311 $ 7.90  Granted - $ -  Vested (7,593) $ 8.34  Cancelled - $ -   Unvested at March 31, 2020 73,718 $ 7.85 	   2019  Number of Options Weighted Average Fair Value at Grant Date  Unvested at January 1, 2019 131,531 $ 13.19  Granted 52,465 $ 4.20  Vested (51,386) $ 14.12  Cancelled (51,299) $ 11.47   Unvested at December 31, 2019 81,311 $ 7.90 
Summary Of RSU Activity		  Number of RSUs Weighted Average Grant Date Fair Value  Outstanding, January 1, 2019 1,394 $ 22.08  Granted - $ -  Vested and Released (464) $ 22.08  Cancelled (930) $ 22.08   Outstanding, December 31, 2019 - $ - 

Warrants (Tables)

Warrants (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Warrants [Abstract]
Summary Of Warrants Outstanding	  Number of Warrants: Warrant Issuance March 31, 2020 December 31, 2019 Exercise Price Expiration Date Liability-classified Warrants  November 2015 Investors 104,168 104,168 $ 63.60 May 2021  November 2015 Placement Agent 279 279 $ 63.60 Nov. 2020  March 2016 Investors 50,651 50,651 $ 50.40 Sept. 2021  September 2016 Investors 67,084 67,084 $ 36.00 Mar. 2022  June 2017 Investors 126,264 126,264 $ 48.00 Dec. 2022  June 2017 Placement Agent 15,153 15,153 $ 49.50 June 2022  October 2017 Investors 136,058 136,058 $ 34.20 Apr. 2023  October 2017 Placement Agent 16,327 16,327 $ 36.72 Oct. 2022  Total liability classified warrants 515,984 515,984  Equity-classified Warrants  October 2018 Investors 480,771 480,771 $ 20.04 Apr. 2024  October 2018 Placement Agent 28,848 28,848 $ 19.50 Oct. 2023  January 2019 Investors 895,886 895,886 $ 9.60 Jan. 2024  Total equity-classified warrants 1,405,505 1,405,505   Total outstanding warrants 1,921,489 1,921,489 	  Number of Warrants:  Warrant Issuance December 31, 2019 December 31, 2018 Exercise Price Expiration Date  Liability-classified Warrants  January 2014 Investors - 39,683 $ 153.60 Jan. 2019  November 2015 Investors 104,168 104,168 $ 63.60 May 2021  November 2015 Placement Agent 279 279 $ 63.60 Nov. 2020  March 2016 Investors 50,651 50,651 $ 50.40 Sept. 2021  September 2016 Investors 67,084 67,084 $ 36.00 Mar. 2022  June 2017 Investors 126,264 126,264 $ 48.00 Dec. 2022  June 2017 Placement Agent 15,153 15,153 $ 49.50 June 2022  October 2017 Investors 136,058 136,058 $ 34.20 Apr. 2023  October 2017 Placement Agent 16,327 16,327 $ 36.72 Oct. 2022  Total liability classified warrants 515,984 555,667   Equity-classified Warrants  October 2018 Investors 480,771 480,771 $ 20.04 Apr. 2024  October 2018 Placement Agent 28,848 28,848 $ 19.50 Oct. 2023  January 2019 Investors 895,886 - $ 9.60 Jan. 2024  Total equity-classified warrants 1,405,505 509,619   Total outstanding warrants 1,921,489 1,065,286 
Summary Of Changes In Warrants Outstanding During The Period	  Number of Warrants  Liability-classified Equity- classified Total Weighted average exercise price  Balance, January 1, 2020 515,984 1,405,505 1,921,489 $ 22.10  Issued during the period - - - $ -  Exercised during the period - - - $ -  Expired during the period - - $ -   Balance, March 31, 2020 515,984 1,405,505 1,921,489 $ 22.10 	  Number of Warrants  Liability-classified Equity- classified Total Weighted average exercise price  Balance, January 1, 2019 555,667 509,619 1,065,286 $ 37.52  Issued during the period - 895,886 895,886 $ 9.60  Exercised during the period - - - $ -  Expired during the period (39,683) - (39,683) $ 153.60   Balance, December 31, 2019 515,984 1,405,505 1,921,489 $ 22.10 
Schedule Of Fair Value Of Warrants Issued	  Fair Value as of: Warrant Issuance: March 31, 2020 December 31, 2019  November 2015 Investors $ 971 $ 55  November 2015 Placement Agent - -  March 2016 Investor 1,240 439  September 2016 Investors 14,639 3,196  June 2017 Investors 30,364 11,736  June 2017 Placement Agent 2,574 845  October 2017 Investors 46,178 23,772  October 2017 Placement Agent 4,143 1,674  Total: $ 100,109 $ 41,717 	  Fair Value as of:  Warrant Issuance: December 31, 2019 December 31, 2018  November 2015 Investors $ 55 $ 234,918  November 2015 Placement Agent - 435  March 2016 Investor 439 160,099  September 2016 Investors 3,196 333,834  June 2017 Investors 11,736 623,324  June 2017 Placement Agent 845 65,149  October 2017 Investors 23,772 801,551  October 2017 Placement Agent 1,674 88,276  Total: $ 41,717 $ 2,307,586 
Schedule Of Assumptions Used In Calculating Fair Value Of Warrants	   March 31, 2020 December 31, 2019  Trading market prices $ 1.80 $ 1.91  Estimated future volatility 100 % 102 %  Dividend - - Estimated future risk-free rate 0.20 - 0.41 % 1.57 -1.72 % Equivalent volatility 113-129 % 85-94 % Equivalent risk-free rate 0.13 -0.19 % 1.57 -1.59 %  Fundamental transaction likelihood 50 % 50 %  Fundamental transaction timing July 2020 April 2020 	  December 31, 2019 December 31, 2018  Trading market prices $ 1.91 $ 11.16  Estimated future volatility 102 % 105 %  Dividend - -  Estimated future risk-free rate 1.57 -1.72 % 2.35 -2.53 %  Equivalent volatility 85-94 % 99-104 %  Equivalent risk-free rate 1.57 -1.59 % 2.51 -2.55 %  Fundamental transaction likelihood 50 % 5 %  Fundamental transaction timing April 2020 End of warrant term 
Schedule Of Unrealized Gain/(Loss) On Fair Value Of Warrants	  For the Three Months Ended March 31,  2020 2019  November 2015 Investors $ (916) $ 197,084  November 2015 Placement Agent - 380  March 2016 Investors (801) 114,799  September 2016 Investors (11,443) 217,869  June 2017 Investors (18,628) 388,391  June 2017 Placement Agent (1,729) 41,911  October 2017 Investors (22,406) 496,501  October 2017 Placement Agent (2,469) 56,436  Total: $ (58,392) $ 1,513,371 	  For the Year Ended December 31,  2019 2018  Expired Warrants $ - $ 64,307  November 2015 Investors 234,863 1,025,132  November 2015 Placement Agent 435 2,501  March 2016 Investors 159,660 537,455  September 2016 Investors 330,638 720,249  June 2017 Investors 611,588 1,358,540  June 2017 Placement Agent 64,304 156,442  October 2017 Investors 777,779 1,504,001  October 2017 Placement Agent 86,602 177,422  Total: $ 2,265,869 $ 5,546,049 

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Income Taxes [Abstract]
Schedule Of Deferred Tax Assets And Valuation Allowance	   March 31, December 31,  2020 2019   Net Operating Loss Carryforwards $ 44,230,000 $ 43,844,000  Stock Compensation Expense 551,000 1,191,000  Book Tax Differences on Assets and Liabilities 163,000 464,000  Valuation Allowance (44,944,000) (45,499,000)   Net Deferred Tax Assets $ - $ - 	   December 31, December 31,  2019 2018   Net Operating Loss Carryforwards $ 43,844,000 $ 41,184,000  Stock Compensation Expense 1,191,000 1,608,000  Book Tax Differences on Assets and Liabilities 464,000 195,000  Valuation Allowance (45,499,000) (42,987,000)   Net Deferred Tax Assets $ - $ - 

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Fair Value Measurements [Abstract]
Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis	  Fair Value Measurements at March 31, 2020  Total Level 1 Level 2 Level 3 Liabilities:  Warrant Liabilities $ 100,109 $ - $ - $ 100,109    Fair Value Measurements at December 31, 2019  Total Level 1 Level 2 Level 3 Assets:  Commercial Paper $ 1,997,400 $ - $ 1,997,400 $ -  Corporate Bonds 999,820 - 999,820 -  Total Assets: $ 2,997,220 $ - $ 2,997,220 $ -  Liabilities:  Warrant Liabilities $ 41,717 $ - $ - $ 41,717 	   Fair Value Measurements at December 31, 2019  Total Level 1 Level 2 Level 3  Assets:  Commercial Paper $ 1,997,400 $ - $ 1,997,400 $ -  Corporate Bonds 999,820 - 999,820 -  Total Assets: $ 2,997,220 $ - $ 2,997,220 $ -   Liabilities:  Warrant Liabilities $ 41,717 $ - $ - $ 41,717     Fair Value Measurements at December 31, 2018  Total Level 1 Level 2 Level 3  Assets:  Corporate Bonds $ 5,981,520 $ - $ 5,981,520 $ -   Liabilities:  Warrant Liabilities $ 2,307,586 $ - $ - $ 2,307,586 
Reconciliation Of Changes In The Fair Value Of Liabilities	  Warrant Liabilities  Balance at January 1, 2020 $ 41,717  Unrealized losses, net 58,392  Balance at March 31, 2020 $ 100,109 	  Warrant Liabilities  Balance at January 1, 2019 $ 2,307,586  Unrealized gains, net (2,265,869)  Balance at December 31, 2019 $ 41,717    Warrant Liabilities  Balance at January 1, 2018 $ 7,853,635  Unrealized gains, net (5,546,049)  Balance at December 31, 2018 $ 2,307,586 

Operations And Organization (De

Operations And Organization (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operations And Organization [Abstract]
Cash, cash equivalents and marketable securities	$ 11,000,000	$ 12,200,000
Accumulated deficit	$ 163,909,446	$ 163,322,676	$ 154,687,242

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies (Narrative) (Details)	Dec. 31, 2019USD ($)
Summary of Significant Accounting Policies [Abstract]
Uninsured cash balance	$ 8,969,547

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies (Schedule Of Estimated Useful Lives) (Details)	12 Months Ended
	Dec. 31, 2019
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Life	7 years
Depreciation Method	straight line
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Life	5 years
Depreciation Method	straight line
Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation Method	straight line
Lab And Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation Method	straight line
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Depreciation Method	straight line
Minimum [Member] | Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Life	5 years
Minimum [Member] | Lab And Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Life	3 years
Minimum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Life	3 years
Maximum [Member] | Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Life	7 years
Maximum [Member] | Lab And Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Life	5 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Life	5 years

Marketable Securities (Details)

Marketable Securities (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	$ 2,995,136
Gross Unrealized Gains	2,084
Fair Value	2,997,220
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	1,996,216
Gross Unrealized Gains	1,184
Fair Value	1,997,400
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	998,920	$ 5,999,356
Gross Unrealized Gains	900
Gross Unrealized Losses		(17,836)
Fair Value	$ 999,820	$ 5,981,520

Prepaid Expenses And Other Cu_3

Prepaid Expenses And Other Current Assets (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Prepaid Expenses And Other Current Assets [Abstract]
Deposits on contracts			$ 618,417
Prepaid expenses and other current assets		$ 447,206	555,430
Total prepaid expenses and other current assets	$ 290,756	$ 447,206	$ 1,173,847

Equipment, Net (Narrative) (Det

Equipment, Net (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019
Equipment, Net [Abstract]
Loss on sale of equipment	$ (9,594)	$ (9,594)

Equipment, Net (Schedule Of Equ

Equipment, Net (Schedule Of Equipment, Net) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total equipment	$ 347,493	$ 347,493	$ 821,590
Less: Accumulated depreciation and amortization	(280,978)	(271,723)	(709,117)
Net carrying amount	66,515	75,770	112,473
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total equipment	67,650	67,650	82,686
Office And Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total equipment	163,440	163,440	159,489
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total equipment			447,653
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total equipment	$ 116,403	$ 116,403	$ 131,762

Accounts Payable And Accrued _3

Accounts Payable And Accrued Expenses (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Payable And Accrued Expenses [Abstract]
Trade payables	$ 891,419	$ 488,285	$ 547,519
Accrued expenses	165,931	471,700	140,637
Accrued research and development contract costs	125,992	221,170	1,782,131
Payroll liabilities	53,665	84,576	682,263
Total accounts payable and accrued expenses	$ 1,237,007	$ 1,265,731	$ 3,152,550

Collaboration and License Agr_2

Collaboration and License Agreements (Details) - USD ($)	Feb. 08, 2020	Feb. 05, 2018	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2003
Other income					$ 368,750
Upfront payment	$ 250,000			$ 3,000,000
Revenue recognized				0
Deferred revenue			$ 600,000	1,500,000
Amount due				1,500,000
Fixed consideration				3,000,000
RX-3117 License [Member]
Upfront payment				2,500,000
RX-3117 Material [Member]
Upfront payment				$ 500,000
RX-0201 [Member]
Other income		$ 368,750
Research and development period				20 years
Reduction of research and development expenses					$ 6,250
Research and development arrangement, one-time fee						$ 1,500,000
Licensing revenue agreement		$ 5,000,000
Percentage of licensing revenue		50.00%
RX-0047 [Member]
Milestone payment	$ 33,000,000
BioSense Global LLC [Member]
Upfront payment			1,650,000
Amount received from upfront payment			1,500,000
Deferred revenue			600,000
Amount due			150,000
Milestone payment			84,500,000
BioSense Global LLC [Member] | RX-3117 License [Member]
Upfront payment			750,000
Revenue recognized			0
BioSense Global LLC [Member] | RX-3117 Material [Member]
Revenue recognized			900,000
Zhejiang HaiChang Biotechnology Co., Ltd. [Member]
Upfront payment			250,000
Fixed consideration			250,000
Zhejiang HaiChang Biotechnology Co., Ltd. [Member] | RX-0201 [Member]
Milestone payment			63,000,000
Zhejiang HaiChang Biotechnology Co., Ltd. [Member] | RX-0047 [Member]
Milestone payment			$ 33,000,000
China [Member]
Milestone payment				$ 126,000,000
Republic of Singapore, China, Hong Kong, Macau and Taiwan [Member]
Milestone payment				$ 100,000,000

Leases (Narrative) (Details)

Leases (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2020USD ($)ft²	Mar. 31, 2019USD ($)	Dec. 31, 2019USD ($)ft²
Lessee, Lease, Description [Line Items]
Discount rate	11.00%		11.00%
Weighted average lease term	1 year 3 months 18 days		1 year 6 months
Operating lease cost | $	$ 36,771	$ 80,279	$ 200,948
Variable lease cost | $	5,693	16,012	28,753
Lease expense | $	$ 42,464	$ 96,291	$ 229,701
Prior Office Space Rental [Member]
Lessee, Lease, Description [Line Items]
Area | ft²			7,193
Office Space Rental [Member]
Lessee, Lease, Description [Line Items]
Area | ft²	5,466		5,466
Laboratory Lease [Member]
Lessee, Lease, Description [Line Items]
Area | ft²			2,552

Leases (Summary Of Right Of Use

Leases (Summary Of Right Of Use Lease Assets And Lease Liabilities) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Right-of-Use Assets	$ 171,870	$ 203,348
Current	144,610	139,765
Long Term	25,790	63,605
Present value of minimum lease payments	$ 170,400	$ 203,370

Leases (Components Of Lease Exp

Leases (Components Of Lease Expense) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 36,771	$ 80,279	$ 200,948
Variable lease cost	5,693	16,012	28,753
Total Lease Cost	$ 42,464	$ 96,291	$ 229,701

Leases (Scheduled Future Minimu

Leases (Scheduled Future Minimum Lease Payments) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2020 (excluding the three months ended March 31, 2020)	$ 117,018
2020		$ 155,280
2021	65,364	65,364
Minimum lease payments	182,382	220,644
Less: Imputed interest	(11,982)	(17,274)
Present value of minimum lease payments	170,400	203,370
Less: current maturities of lease obligations	(144,610)	(139,765)
Long-term lease obligations	$ 25,790	$ 63,605

Net Loss Per Common Share (Deta

Net Loss Per Common Share (Details) - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Options, Restricted Stock Units And Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities	2,070,511	2,126,063	1,322,602

Common Stock (Details)

Common Stock (Details)	Apr. 12, 2019$ / sharesshares	Jan. 25, 2019USD ($)$ / sharesshares	Oct. 19, 2018USD ($)$ / sharesshares	Mar. 31, 2020$ / sharesshares	Dec. 31, 2019$ / sharesshares	Dec. 31, 2018$ / sharesshares	Aug. 30, 2018shares	Aug. 29, 2018shares
Class of Stock [Line Items]
Reverse stock split	0.083
Common Stock, Par Value | $ / shares	$ 0.0001			$ 0.0001	$ 0.0001	$ 0.0001
Common Stock, Shares Authorized | shares	75,000,000			75,000,000	75,000,000	75,000,000	75,000,000	50,000,000
Preferred Stock, Shares Authorized | shares	10,000,000			10,000,000	10,000,000	10,000,000
Shares issued | shares		895,834	480,770
Warrants issued | shares		895,886	480,771		895,886
Warrants issued per share of stock issued in unit offering | $ / shares		$ 1	$ 1
Proceeds from issuance | $		$ 8,600,000	$ 7,500,000
Share price | $ / shares		$ 9.60	$ 15.60
Warrants exercise price | $ / shares		$ 9.60	$ 20.04
Public offering closing costs | $		$ 1,046,172	$ 896,117
Fair value of placement agent warrants | $			286,906
Cash paid in exchange for legal services | $			$ 627,211
Placement Agent Warrant [Member]
Class of Stock [Line Items]
Warrants exercise price | $ / shares			$ 19.50
Warrants issued included in closing costs | shares			28,848

Stock-Based Compensation (Narra

Stock-Based Compensation (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefit from share-based compensation	$ 0	$ 0
Valuation allowance on deferred tax assets	100.00%	100.00%
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding	149,022	204,574	255,922
Percentage of Event Occurence to Vest		100.00%
Stock options granted		52,465
Stock option exercise price		$ 6.41
Intrinsic value of options exercised		$ 0	$ 0
Weighted average fair value at grant date, Vested		$ 4.20	$ 12.48
Unrecognized compensation cost	$ 501,655	$ 577,976
Weighted average vesting period, years	1 year 8 months 12 days	2 years
The 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options authorized for issuance	283,333
Shares available for issuance	136,936	93,882
The 2013 Plan [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding	144,366	187,420
Options authorized for issuance		283,333
The 2003 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	0
The 2003 Plan [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding	4,656	17,154
Shares available for issuance		0
Share-based Compensation Award, Tranche One [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Share-based Compensation Award, Tranche Two [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		2.77%
Minimum [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Maximum [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Expiration of options from grant date, years		10 years
Exercise Price Range $5.23 to $7.45 [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted		52,465
Stock option grants fair value		$ 220,540
Exercise Price Range $5.23 to $7.45 [Member] | Minimum [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option exercise price		$ 5.23
Exercise Price Range $5.23 to $7.45 [Member] | Maximum [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option exercise price		$ 7.45
Exercise Price Range $13.08 to $27.48 [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted			123,587
Stock option grants fair value			$ 1,540,866
Exercise Price Range $13.08 to $27.48 [Member] | Minimum [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option exercise price			$ 13.08
Exercise Price Range $13.08 to $27.48 [Member] | Maximum [Member] | Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option exercise price			$ 27.48

Stock-Based Compensation (Summa

Stock-Based Compensation (Summary Of Stock Compensation Expense) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share Based Compensation	$ 76,302	$ 161,000	$ 456,750	$ 1,228,335
General and administrative [Member]
Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share Based Compensation	72,420	116,679	393,483	883,855
Research and development [Member]
Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share Based Compensation	$ 3,882	$ 44,321	$ 63,267	$ 344,480

Stock-Based Compensation (Sched

Stock-Based Compensation (Schedule Of Assumptions Made In Calculating The Fair Value Of Options) (Details) - Stock Option [Member]	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum	74.00%	69.00%
Expected volatility, maximum	75.00%	73.00%
Risk-free interest rate, minimum	1.90%	2.30%
Risk-free interest rate, maximum	2.60%	2.90%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years	6 years

Stock-Based Compensation (Sum_2

Stock-Based Compensation (Summary Of Share-Based Transactions ) (Details) - Stock Option [Member] - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Options, Oustanding	204,574	255,922
Number of Options, Granted		52,465
Number of Options, Exercised
Number of Options, Expired	(2,498)	(2,080)
Number of Options, Cancelled	(53,054)	(101,733)
Number of Options, Oustanding	149,022	204,574	255,922
Weighted Average Exercise Price, Outstanding	$ 35.60	$ 41.88
Weighted Average Exercise Price, Granted		6.41
Weighted Average Exercise Price, Exercised
Weighted Average Exercise Price, Expired	159.60	97.78
Weighted Average Exercise Price, Cancelled	60.40	34.99
Weighted Average Exercise Price, Outstanding	$ 24.69	$ 35.60	$ 41.88
Weighted Average Remaining Contractual Term, Outstanding	7 years 9 months 18 days	7 years 3 months 18 days	7 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding
Number of Options, Exercisable	75,304	123,263
Weighted Average Exercise Price, Exercisable	$ 37.16	$ 51.15
Weighted Average Remaining Contractual Term, Exercisable	7 years	6 years 2 months 12 days
Aggregate Intrinsic Value, Exercisable

Stock-Based Compensation (Sum_3

Stock-Based Compensation (Summary Of Unvested Shares) (Details) - Stock Option [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Options, Granted		52,465
Nonvested Options [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Options, Unvested	81,311	131,531
Number of Options, Granted		52,465
Number of Options, Vested	(7,593)	(51,386)
Number of Options, Cancelled		(51,299)
Number of Options, Unvested	73,718	81,311
Weighted Average Fair Value at Grant Date, Unvested	$ 7.90	$ 13.19
Weighted Average Fair Value at Grant Date, Granted		4.20
Weighted Average Fair Value at Grant Date, Vested	8.34	14.12
Weighted Average Fair Value at Grant Date, Cancelled		11.47
Weighted Average Fair Value at Grant Date, Unvested	$ 7.85	$ 7.90

Stock-Based Compensation (Sum_4

Stock-Based Compensation (Summary Of RSU Activity) (Details) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSUs, Outstanding | shares	1,394
Number of RSUs, Granted | shares
Number of RSUs, Vested and Released | shares	(464)
Number of RSUs, Cancelled | shares	(930)
Number of RSUs, Outstanding | shares
Weighted Average Grant Date Fair Value, Outstanding | $ / shares	$ 22.08
Weighted Average Grant Date Fair Value, Granted | $ / shares
Weighted Average Grant Date Fair Value, Vested and Released | $ / shares	22.08
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	22.08
Weighted Average Grant Date Fair Value, Outstanding | $ / shares

Warrants (Narrative) (Details)

Warrants (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Warrants [Abstract]
Average remaining contractual life of warrants outstanding	3 years 4 months 24 days	3 years 8 months 12 days

Warrants (Summary Of Warrants O

Warrants (Summary Of Warrants Outstanding) (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Jan. 25, 2019	Dec. 31, 2018	Oct. 19, 2018
Class of Warrant or Right [Line Items]
Number of Warrants	1,921,489	1,921,489		1,065,286
Exercise Price			$ 9.60		$ 20.04
Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	515,984	515,984		555,667
Equity-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	1,405,505	1,405,505		509,619
January 2014 Investor Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants				39,683
Exercise Price		$ 153.60
Expiration Date		2019-01
November 2015 Investor Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	104,168	104,168		104,168
Exercise Price	$ 63.60	$ 63.60
Expiration Date	2021-05	2021-05
November 2015 Placement Agent Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	279	279		279
Exercise Price	$ 63.60	$ 63.60
Expiration Date	2020-11	2020-11
March 2016 Investor Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	50,651	50,651		50,651
Exercise Price	$ 50.40	$ 50.40
Expiration Date	2021-09	2021-09
September 2016 Investor Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	67,084	67,084		67,084
Exercise Price	$ 36	$ 36
Expiration Date	2022-03	2022-03
June 2017 Investor Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	126,264	126,264		126,264
Exercise Price	$ 48	$ 48
Expiration Date	2022-12	2022-12
June 2017 Placement Agent Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	15,153	15,153		15,153
Exercise Price	$ 49.50	$ 49.50
Expiration Date	2022-06	2022-06
October 2017 Investor Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	136,058	136,058		136,058
Exercise Price	$ 34.20	$ 34.20
Expiration Date	2023-04	2023-04
October 2017 Placement Agent Warrants [Member] | Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	16,327	16,327		16,327
Exercise Price	$ 36.72	$ 36.72
Expiration Date	2022-10	2022-10
October 2018 Investor Warrants [Member] | Equity-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	480,771	480,771		480,771
Exercise Price	$ 20.04	$ 20.04
Expiration Date	2024-04	2024-04
October 2018 Placement Agent Warrants [Member] | Equity-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	28,848	28,848		28,848
Exercise Price	$ 19.50	$ 19.50
Expiration Date	2023-10	2023-10
January 2019 Investor Warrants [Member] | Equity-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of Warrants	895,886	895,886
Exercise Price	$ 9.60	$ 9.60
Expiration Date	2024-01	2024-01

Warrants (Summary Of Changes In

Warrants (Summary Of Changes In Warrants Outstanding During The Period) (Details) - $ / shares	Jan. 25, 2019	Oct. 19, 2018	Mar. 31, 2020	Dec. 31, 2019
Class of Warrant or Right [Line Items]
Number of warrants, Outstanding			1,921,489	1,065,286
Number of warrants, issued	895,886	480,771		895,886
Number of warrants, Exercised
Number of warrants, Expired				(39,683)
Number of warrants, Outstanding			1,921,489	1,921,489
Weigted average exercise price, Outstanding			$ 22.10	$ 37.52
Weighted average exercise price, Issued				9.60
Weighted average exercise price, Exercised
Weighted average exercise price, Expired				153.60
Weigted average exercise price, Outstanding			$ 22.10	$ 22.10
Liability-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of warrants, Outstanding			515,984	555,667
Number of warrants, issued
Number of warrants, Exercised
Number of warrants, Expired				(39,683)
Number of warrants, Outstanding			515,984	515,984
Equity-Classified Warrants [Member]
Class of Warrant or Right [Line Items]
Number of warrants, Outstanding			1,405,505	509,619
Number of warrants, issued				895,886
Number of warrants, Exercised
Number of warrants, Expired
Number of warrants, Outstanding			1,405,505	1,405,505

Warrants (Schedule Of Fair Valu

Warrants (Schedule Of Fair Value Of Warrants Issued) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Fair value	$ 100,109	$ 41,717	$ 2,307,586
November 2015 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	971	55	234,918
November 2015 Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value			435
March 2016 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	1,240	439	160,099
September 2016 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	14,639	3,196	333,834
June 2017 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	30,364	11,736	623,324
June 2017 Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	2,574	845	65,149
October 2017 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	46,178	23,772	801,551
October 2017 Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Fair value	$ 4,143	$ 1,674	$ 88,276

Warrants (Schedule Of Assumptio

Warrants (Schedule Of Assumptions Used In Calculating Fair Value Of Warrants) (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Trading market prices	$ 1.80	$ 1.91	$ 11.16
Estimated future volatility	100.00%	102.00%	105.00%
Dividend
Fundamental transaction likelihood	50.00%	50.00%	5.00%
Fundamental transaction timing	2020-07	2020-04
Fundamental transaction timing			End of warrant term
Minimum [Member]
Class of Warrant or Right [Line Items]
Estimated future risk-free rate	0.20%	1.57%	2.35%
Equivalent volatility	113.00%	85.00%	99.00%
Equivalent risk-free rate	0.13%	1.57%	2.51%
Maximum [Member]
Class of Warrant or Right [Line Items]
Estimated future risk-free rate	0.41%	1.72%	2.53%
Equivalent volatility	129.00%	94.00%	104.00%
Equivalent risk-free rate	0.19%	1.59%	2.55%

Warrants (Schedule Of Unrealize

Warrants (Schedule Of Unrealized Gain/(Loss) On Fair Value Of Warrants) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	$ (58,392)	$ 1,513,371	$ 2,265,869	$ 5,546,049
Expired Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants				64,307
November 2015 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	(916)	197,084	234,863	1,025,132
November 2015 Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants		380	435	2,501
March 2016 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	(801)	114,799	159,660	537,455
September 2016 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	(11,443)	217,869	330,638	720,249
June 2017 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	(18,628)	388,391	611,588	1,358,540
June 2017 Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	(1,729)	41,911	64,304	156,442
October 2017 Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	(22,406)	496,501	777,779	1,504,001
October 2017 Placement Agent Warrants [Member]
Class of Warrant or Right [Line Items]
Unrealized (loss) gain on fair value of warrants	$ (2,469)	$ 56,436	$ 86,602	$ 177,422

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Provision for Income Taxes
Operating loss carry-forward	$ 157,964,000		$ 156,586,000	147,086,000
Net operating loss carry-forwards expiration			Dec. 31, 2021
Federal And State [Member]
Operating Loss Carryforwards [Line Items]
Provision for Income Taxes	$ 0	$ 0	$ 0	$ 0

Income Taxes (Schedule Of Defer

Income Taxes (Schedule Of Deferred Tax Assets And Valuation Allowance) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Abstract]
Net Operating Loss Carryforwards	$ 44,230,000	$ 43,844,000	$ 41,184,000
Stock Compensation Expense	551,000	1,191,000	1,608,000
Book Tax Differences on Assets and Liabilities	163,000	464,000	195,000
Valuation Allowance	(44,944,000)	(45,499,000)	(42,987,000)
Net Deferred Tax Assets

Commitments And Contingencies (

Commitments And Contingencies (Details) - USD ($)	Jun. 22, 2009	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Feb. 05, 2018
Commitments And Contingencies [Line Items]
Estimated cost to complete contracts		$ 800,000		$ 1,750,000
One-time milestone payment	$ 1,000,000
First achievement of marketing approvals	30 days
Employer matching contribution		100.00%		100.00%
Maximum percentage of employee's gross pay		3.00%		3.00%
Employer matching contribution on deferral		50.00%		50.00%
Percentage of employee's gross pay		2.00%		2.00%
Expense related to matching contribution		$ 11,229	$ 27,879	$ 71,568	$ 120,558
RX-0201 [Member]
Commitments And Contingencies [Line Items]
Royalty						50.00%
Licensing revenue agreement						$ 5,000,000
Percentage of licensing revenue						50.00%
Maximum [Member]
Commitments And Contingencies [Line Items]
Contract term, months		36 months		36 months
Maximum [Member] | RX-0201 [Member]
Commitments And Contingencies [Line Items]
Licensing revenue agreement						$ 5,000,000
Minimum [Member]
Commitments And Contingencies [Line Items]
Contract term, months		2 months		2 months
Minimum [Member] | RX-0201 [Member]
Commitments And Contingencies [Line Items]
Licensing revenue						$ 5,000,000

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurements [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0	$ 0	$ 0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0	0	0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount	0	0	0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	$ 0	$ 0	$ 0

Fair Value Measurements (Schedu

Fair Value Measurements (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:		$ 2,997,220
Warrant Liabilities	$ 100,109	41,717	$ 2,307,586
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:		999,820	5,981,520
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:		1,997,400
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:
Warrant Liabilities
Level 1 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:
Level 1 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:		2,997,220
Warrant Liabilities
Level 2 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:		999,820	5,981,520
Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:		1,997,400
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:
Warrant Liabilities	$ 100,109	41,717	$ 2,307,586
Level 3 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:
Level 3 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets:

Fair Value Measurements (Reconc

Fair Value Measurements (Reconciliation Of Changes In The Fair Value Of Liabilities) (Details) - Warrant Liabilities [Member] - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance	$ 41,717	$ 2,307,586	$ 7,853,635
Unrealized losses, net	58,392	(2,265,869)	(5,546,049)
Balance	$ 100,109	$ 41,717	$ 2,307,586

Subsequent Event (Details)

Subsequent Event (Details) - USD ($)	Feb. 08, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Upfront payment	$ 250,000	$ 3,000,000
RX-0201 And RX-0301 [Member]
Subsequent Event [Line Items]
Milestone payment	63,000,000
RX-0047 [Member]
Subsequent Event [Line Items]
Milestone payment	$ 33,000,000