Exicure (XCUR) 10-K 8 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Mar. 05, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	EXICURE, INC.
Entity Central Index Key	1,698,530
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		44,358,000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Public Float			$ 117.6

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 26,268	$ 25,764
Unbilled revenue receivable	3	13
Receivable from related party	10	17
Prepaid expenses and other assets	1,382	1,844
Total current assets	27,663	27,638
Property and equipment, net	1,061	1,317
Other noncurrent assets	32	32
Total assets	28,756	28,987
Current liabilities:
Accounts payable	500	1,049
Accrued expenses and other current liabilities	1,543	1,273
Current portion of deferred revenue	0	1,034
Total current liabilities	2,043	3,356
Long-term debt, net	4,925	4,855
Common stock warrant liability	797	523
Other noncurrent liabilities	39	278
Total liabilities	7,804	9,012
Stockholders’ equity:
Common stock, $0.0001 par value per share; 200,000,000 shares authorized, 44,358,000 issued and outstanding, December 31, 2018; 39,300,823 shares issued and outstanding, December 31, 2017	4	4
Additional paid-in capital	75,942	53,586
Accumulated deficit	(54,994)	(33,615)
Total stockholders' equity	20,952	19,975
Total liabilities and stockholders’ equity	$ 28,756	$ 28,987

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	44,358,000	39,300,823
Common stock, shares outstanding (in shares)	44,358,000	39,300,823

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 118	$ 9,719
Operating expenses:
Research and development expense	14,119	13,080
General and administrative expense	7,818	7,046
Total operating expenses	21,937	20,126
Operating loss	(21,819)	(10,407)
Other income (expense), net:
Interest expense	(672)	(795)
Other income (loss), net	78	191
Total other income (loss), net	(594)	(604)
Net loss	$ (22,413)	$ (11,011)
Basic and diluted loss per common share (in dollars per share)	$ (0.54)	$ (1.09)
Basic and diluted weighted-average common shares outstanding (in shares)	41,189,177	10,119,569

CONSOLIDATED STATEMENT OF CHANG

CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in- Capital	Accumulated Deficit	Series CNon-Redeemable Preferred Stock	Series B-2Non-Redeemable Preferred Stock	Series B-1Non-Redeemable Preferred Stock	Series ANon-Redeemable Preferred Stock
Beginning balance (in shares) at Dec. 31, 2016		131,644			11,239,359	1,403,984	2,451,560	11,381,640
Beginning balance at Dec. 31, 2016	$ 2,448	$ 0	$ (17,578)	$ (22,604)	$ 33,483	$ 3,641	$ 5,371	$ 135
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (in shares)		58,440
Exercise of options	43		43
Equity-based compensation	1,462		1,462
Share conversion in connection with the Merger (in shares)		28,556,543			(11,239,359)	(1,403,984)	(2,451,560)	(11,381,640)
Share conversion in connection with the Merger	(31)	$ 3	42,596		$ (33,483)	$ (3,641)	$ (5,371)	$ (135)
Issuance of common stock in private placement, net (in shares)		10,554,196
Issuance of common stock in private placement, net	27,064	$ 1	27,063
Net loss	(11,011)			(11,011)
Ending balance (in shares) at Dec. 31, 2017		39,300,823			0	0	0	0
Ending balance at Dec. 31, 2017	19,975	$ 4	53,586	(33,615)	$ 0	$ 0	$ 0	$ 0
Adoption of new accounting standard - ASC 606 at Dec. 31, 2017	1,034			1,034
Beginning balance, adjusted at Dec. 31, 2017	$ 21,009	$ 4	53,586	(32,581)	$ 0	$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (in shares)	22,494	22,494
Exercise of options	$ 41		41
Equity-based compensation	1,809		1,809
Issuance of common stock to consultants, net (in shares)		145,466
Issuance of common stock to consultants, net	436		436
Issuance of common stock in private placement, net (in shares)		4,889,217
Issuance of common stock in private placement, net	20,070		20,070
Net loss	(22,413)			(22,413)
Ending balance (in shares) at Dec. 31, 2018		44,358,000			0	0	0	0
Ending balance at Dec. 31, 2018	$ 20,952	$ 4	$ 75,942	$ (54,994)	$ 0	$ 0	$ 0	$ 0

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (22,413)	$ (11,011)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	358	232
Equity-based compensation	1,809	1,462
Amortization of long-term debt issuance costs and fees	96	189
Other	400	0
Change in fair value of warrant liabilities	274	(214)
Changes in operating assets and liabilities:
Unbilled revenue receivable and accounts receivable	10	(13)
Receivable from related party	7	(2)
Prepaid expenses and other current assets	498	(1,442)
Accounts payable	(557)	195
Accrued expenses and other current liabilities	270	(906)
Deferred revenue	0	(8,276)
Other noncurrent liabilities	(239)	(3)
Net cash used in operating activities	(19,487)	(19,789)
Cash flows from investing activities:
Capital expenditures	(94)	(926)
Net cash used in investing activities	(94)	(926)
Cash flows from financing activities:
Proceeds from common stock offering	22,001	31,513
Proceeds from exercise of common stock options	41	43
Repayment of long-term debt	0	(1,001)
Payment of long-term debt fees and issuance costs	(26)	0
Payment of common stock financing costs	(1,931)	(3,699)
Net cash provided by financing activities	20,085	26,856
Net increase in cash and cash equivalents	504	6,141
Cash and cash equivalents - beginning of period	25,764	19,623
Cash and cash equivalents - end of period	26,268	25,764
Non-cash financing activities:
Issuance of common stock for professional services	436	0
Issuance of common stock warrants	0	536
Common stock issuance costs (accounts payable and accrued expenses)	0	214
Non-cash investing activities:
Capital expenditures (accounts payable and accrued expenses)	$ 8	$ 120

Description of Business and Bas

Description of Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Description of Business and Basis of Presentation	Description of Business and Basis of Presentation Description of Business Exicure is a clinical-stage biotechnology company developing therapeutics for immuno-oncology, inflammatory diseases and genetic disorders based on the Company’s proprietary Spherical Nucleic Acid (“SNA”) technology. We believe the design of the Company’s SNAs gives rise to distinct chemical and biological properties that may provide advantages over other nucleic acid therapeutics and enable therapeutic activity outside of the liver. The Company intends to build a leading nucleic acid therapeutics company focused on the discovery and development of therapeutics based on the Company’s proprietary SNA technology, either on its own or in collaboration with pharmaceutical partners. Throughout these consolidated financial statements, the terms “the Company” and “Exicure” refer to Exicure, Inc. and its 100% owned subsidiary, Exicure Operating Company. Exicure Operating Company holds all material assets, and conducts all business activities and operations, of the Company. The Merger On September 26, 2017, pursuant to the merger agreement, Max-1 Acquisition Sub, Inc., a wholly-owned subsidiary of Max-1 Acquisition Corporation (“Max-1”), merged with and into Exicure Operating Company (f/k/a Exicure, Inc.), a privately-held Delaware corporation referred to herein as Exicure OpCo, with Exicure OpCo remaining as the surviving entity and a wholly-owned operating subsidiary of Max-1 (the “Merger”). The Merger was effective as of September 26, 2017 (the “Effective Time”), upon the filing of a Certificate of Merger with the Secretary of State of the State of Delaware. At the Effective Time, the legal existence of Max-1 Acquisition Sub, Inc. ceased. At the Effective Time, each share of Exicure OpCo common and preferred stock (other than shares of Exicure OpCo’s Series C preferred stock) issued and outstanding immediately prior to the closing of the Merger was converted into 0.49649 shares of Max-1’s common stock, and each share of Exicure OpCo’s Series C preferred stock issued and outstanding immediately prior to the closing of the Merger was converted into 0.7666652 shares of Max-1’s common stock. As a result, an aggregate of 26,666,627 shares of Max-1’s common stock were issued to the holders of Exicure OpCo’s capital stock, which is incremental to the 2,080,000 shares of Max-1 common stock that were outstanding immediately prior to the Merger. In addition, pursuant to the Merger Agreement, options to purchase 7,414,115 shares of Exicure OpCo common stock issued and outstanding immediately prior to the closing of the Merger were assumed by Max-1 and converted into options to purchase 3,680,997 shares of Max-1’s common stock. After the filing of the Certificate of Merger with the Secretary of State of the State of Delaware, Max-1 changed its name to Exicure, Inc. The Merger is considered a “reverse merger,” whereby Exicure OpCo is considered the accounting acquirer in the Merger. Exicure OpCo was determined to be the accounting acquirer based on the terms of the Merger and other factors including: (i) legacy Exicure OpCo shareholders own approximately 94% of the combined company on a fully diluted basis immediately following the closing of the Merger, (ii) legacy Exicure OpCo directors will hold all six board seats of the combined company, and (iii) legacy Exicure OpCo management will hold all positions in management of the combined company. The transaction is accounted for as an asset acquisition rather than a business combination because as of the acquisition date, Max-1 does not meet the definition of a business as defined by accounting principles generally accepted in the United States of America (“GAAP”). Consequently, the assets, liabilities and operations that are reflected in Exicure’s historical financial statements prior to the Merger will be those of Exicure OpCo, and the consolidated financial statements after completion of the Merger will include the assets, liabilities and results of operations of Exicure OpCo up to the day prior to the closing of the Merger and the assets, liabilities and results of operations of the combined company from and after the closing date of the Merger. The assets and liabilities of Max-1 included in the accompanying consolidated financial statements are recorded at the historical cost basis of Max-1. In these consolidated financial statements, unless otherwise indicated, all share and per share figures are retrospectively adjusted to reflect the conversion of each share of Exicure OpCo common and preferred stock (other than shares of Exicure OpCo’s Series C preferred stock), preferred stock warrant liability, and common stock options issued and outstanding immediately prior to the closing of the Merger into 0.49649 shares of the Company’s common stock, and each share of Exicure OpCo’s Series C preferred stock issued and outstanding immediately prior to the closing of the Merger into 0.7666652 shares of the Company’s common stock. Capitalization Prior to the Merger AuraSense Therapeutics, LLC was formed on June 13, 2011 as a wholly owned subsidiary of AuraSense, LLC, but did not conduct substantive business until December 12, 2011, which is considered the inception date. On December 12, 2011, AuraSense, LLC contributed the assets and liabilities comprising the business of the Company to the Company through a Bill of Sale and Assumption Agreement. Pursuant to this agreement AuraSense, LLC received 11,381,611 Class A Units of the Company. The assets and liabilities contributed by AuraSense, LLC were transferred at their historical cost and consisted of an unbilled revenue receivable of $143 , scientific equipment of $309 and a liability of $317 for accrued legal expenses related to patent protection. The net book value of AuraSense, LLC’s contribution at inception was $135 . Also on December 12, 2011, the Company and AuraSense, LLC entered into a Partial Assignment of License Agreement whereby certain license rights held by AuraSense, LLC pursuant to a License Agreement with Northwestern University were assigned to the Company. Under the terms of the License Agreement and the Partial Assignment of License Agreement, Northwestern University received 1.0% of the Class A units received by AuraSense, LLC in the formation transaction, which amounted to 113,816 units. On July 9, 2015, AuraSense Therapeutics, LLC was converted into AuraSense Therapeutics, Inc., a Delaware corporation, and on the same date changed its name to Exicure, Inc., which actions together are referred to in these Notes to Consolidated Financial Statements as the corporate conversion. In connection with the corporate conversion, each common unit, Class A unit, Class B-1 unit, Class B-2 unit and Class C unit of AuraSense Therapeutics, LLC issued and outstanding immediately prior to the effectiveness of the corporate conversion was converted into one share of common stock, Series A preferred stock, Series B-1 preferred stock, Series B-2 preferred stock and Series C preferred stock of Exicure OpCo, respectively. No preferred stock was provided in consideration for fractional membership units. Each outstanding option to purchase one common unit of AuraSense Therapeutics, LLC was converted into an option to purchase one share of common stock of Exicure OpCo. In connection with the corporate conversion, the accumulated deficit of AuraSense Therapeutics, LLC of $18,837 was reclassified to Additional paid in capital. Refer to Note 6, Stockholders’ Equity, for more information on capital stock transactions. Basis of Presentation The accompanying consolidated financial statements as of December 31, 2018 and 2017, and for the years then ended, have been presented in conformity with generally accepted accounting principles in the United States (“GAAP”). Principles of Consolidation The accompanying consolidated financial statements include the accounts of Exicure, Inc. and its 100% owned subsidiary, Exicure Operating Company. All intercompany transactions and accounts are eliminated in consolidation. Going Concern As of December 31, 2018, the Company has generated an accumulated deficit of $73,831 since inception and expects to incur significant expenses and negative cash flows for the foreseeable future. Based on the Company’s current operating plans, it believes that existing working capital at December 31, 2018 is sufficient to fund its current operating plans into January 2020. Management believes that it will be able to obtain additional working capital through equity financings, partnerships and licensing, or other arrangements, to fund operations. However, there can be no assurance that such additional financing will be available and, if available, can be obtained on terms acceptable to the Company. If the Company is unable to obtain such additional financing, the Company will need to reevaluate future operating plans. Accordingly, there is substantial doubt regarding the Company’s ability to continue as a going concern. The accompanying consolidated financial statements have been prepared as though the Company will continue as a going concern, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. Use of Estimates The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and 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. Management bases its estimates on certain assumptions which it believes are reasonable in the circumstance and while actual results could differ from those estimates, management does not believe that any change in those assumptions in the near term would have a significant effect on the Company’s financial position, results of operations or cash flows. Actual results in future periods could differ from those estimates. Revision of Prior Period Financial Statements In connection with preparing our condensed consolidated interim financial information for the three months ended March 31, 2018, we identified errors that affected prior interim and annual periods related to the timing of recognition of research and development expense related to a contract for the clinical trial of one of our therapeutic candidates. We evaluated whether our previously issued consolidated financial statements were materially misstated and concluded that the errors individually and in the aggregate were not material to any of our previously issued financial statements. We revised the financial statements to correct the immaterial errors, and the accompanying comparative financial statements reflect these corrections. The correction of the errors increased prepaid expense and other current assets by $933 , decreased accrued expenses by $95 , and decreased accumulated deficit by $1,028 at December 31, 2017; and decreased research and development expense, operating loss, and net loss by $1,028 and loss per share by $0.10 for the year ended December 31, 2017.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Cash and cash equivalents The Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents. Accounts receivable and unbilled revenue receivable Accounts receivable and unbilled revenue receivable consist of reimbursement for research and development activities in connection with the research collaboration, license, and option agreement with Purdue Pharma L.P. (“Purdue”). The Company’s management believes these receivables are fully collectible. Fair value of financial instruments The carrying amounts of financial instruments, which include cash and cash equivalents and accounts payable, approximate their respective fair values due to the relatively short-term nature of these instruments. Management believes that the Company’s long-term debt bears interest at the prevailing market rate for instruments with similar characteristics and, accordingly, the carrying value of long-term debt also approximates their fair value. Concentrations of credit risk and other risks and uncertainties Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. As of December 31, 2018 and 2017, the Company had cash and cash equivalents of $26,268 and $25,764 , respectively. The cash balances at each respective period were maintained at two institutions. These deposits exceed federally insured limits. During the years ended December 31, 2018 and 2017, one counterparty accounted for all of the Company’s revenue. The Company is currently not profitable and no assurance can be provided that it will ever be profitable. The Company’s research and development activities have required significant investment since inception and operations are expected to continue to require cash investment in excess of its revenues. See also Note 1, Description of Business and Basis of Presentation—Going Concern , for more information. The Company is subject to risks common in therapeutic development including, but not limited to, therapeutic candidates that appear promising in the early phases of development often fail because they prove to be inefficacious or unsafe, clinical trial results are unsuccessful, regulatory bodies may not approve the therapeutic or the therapeutic may not be economical in production or distribution. The Company is also subject to risks common to biotechnology firms including, but not limited to new and disruptive technological innovations, dependence on key personnel, protection of proprietary technology, the validity of and continued access to its owned and licensed intellectual property, limitations on the supply of critical materials, compliance with governmental regulations and market acceptance. Property and equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the various classes of property and equipment, which range from three to seven years. Leasehold improvements are amortized using the straight-line method over the shorter of the remaining terms of the respective leases or the estimated lives of the assets. Depreciation begins at the time the asset is placed in service. Property and equipment are reviewed for impairment at least annually or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. No impairment losses were recorded from inception in December 2011 through December 31, 2018. Common stock warrant liability Freestanding warrants related to shares that are redeemable, contingently redeemable, or for purchases of common stock that are not indexed to the Company’s own stock are classified as a liability on the Company’s balance sheet. The common stock warrants are recorded at fair value, estimated using the Black-Scholes option-pricing model, and marked to market at each balance sheet date with changes in the fair value of the liability recorded in other income (expense), net in the statements of operations. Revenue recognition Effective January 1, 2018, the Company adopted the provisions of Accounting Standards Codification (“ASC”) 606, Revenue from Contracts with Customers using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance, while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605). Under ASC 605, the Company’s revenue recognition accounting policy was consistent with ASC 606 revenue recognition accounting policies, except the Company used to recognize upfront license fees on a straight line basis. Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that are within the scope of ASC 606, the Company performs the following five steps: 1. Identify the contract with the customer. A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance, and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. The Company applies judgment in determining the customer’s intent and ability to pay, which is based on a variety of factors including the customer’s historical payment experience, or in the case of a new customer, published credit and financial information pertaining to the customer. 2. Identify the performance obligations in the contract. Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are both capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. 3. Determine the transaction price. The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method, depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment. 4. Allocate the transaction price to performance obligations in the contract. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. However, if a series of distinct services that are substantially the same qualifies as a single performance obligation in a contract with variable consideration, the Company must determine if the variable consideration is attributable to the entire contract or to a specific part of the contract. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. 5. Recognize revenue when or as the Company satisfies a performance obligation. The Company satisfies performance obligations either over time or at a point in time. Revenue is recognized over time if either (i) the customer simultaneously receives and consumes the benefits provided by the entity’s performance, (ii) the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or (iii) the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. Examples of control are using the asset to produce goods or services, enhance the value of other assets, or settle liabilities, and holding or selling the asset. Licenses of intellectual property : If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from consideration allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the licenses. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: At the inception of each arrangement that includes development milestone payments, the Company evaluates the probability of reaching the milestones and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur in the future, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received and therefore revenue recognized is constrained as management is unable to assert that a reversal of revenue would not be possible. The transaction price is then allocated to each performance obligation on a relative standalone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues and earnings in the period of adjustment. Royalties : For arrangements that include sales-based royalties, including milestone payments based on levels of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaboration agreements. For the years ended December 31, 2018 and 2017, the Company’s only revenue recognized is related to the Purdue Collaboration (see Note 3). Equity-based compensation The Company measures the cost of common stock option awards at fair value and records the cost of the awards, net of estimated forfeitures, on a straight-line basis over the requisite service period. The Company measures fair value for all common stock options using the Black-Scholes option-pricing model. For all common stock option awards to employees, the fair value measurement date is the date of grant and the requisite service period is the period over which the employee is required to provide service in exchange for the common stock option awards, which is generally the vesting period. For all common stock option awards to nonemployees, the Company remeasures fair value at each financial statement reporting date and recognizes compensation expense as services are rendered, generally on a straight-line basis. Segments and geographic information The Company has determined it has one reporting segment. Disaggregating the Company’s operations is impracticable because the Company’s research and development activities and its assets overlap and management reviews its business as a single operating segment. Thus, discrete financial information is not available by more than one operating segment. All long-lived assets of the Company are located in the United States. Deferred rent Deferred rent consists of rent escalation payment terms, tenant improvement allowances and other incentives received from the landlord related to the Company’s operating lease and is presented in “Other noncurrent assets” in the accompanying balance sheet. Rent escalation represents the difference between actual operating lease payments due and straight-line rent expense, which is recorded by the Company over the term of the lease. Tenant improvement allowances and other incentives are recorded as deferred rent and amortized as a reduction of periodic rent expense, over the term of the applicable lease. Research and development expense Research and development expense includes wages, benefits, research materials, external services, legal fees related to patent protection, overhead and other expenses directly related to research and development operations. Research and development costs are expensed as incurred in accordance with ASC 730, Research and Development. Research and development costs that are paid in advance of performance are deferred as a prepaid expense and recognized as expense as the services are provided. Income taxes From inception through July 9, 2015, the Company was a Delaware LLC for federal and state tax purposes and, therefore, all items of income or loss through July 9, 2015 flowed through to the members of AuraSense Therapeutics, LLC. Effective July 9, 2015, the Company converted from an LLC to a C corporation for federal and state income tax purposes. Accordingly, prior to the conversion to a C corporation, the Company did not record deferred tax assets or liabilities or have any net operating loss carryforwards. The Company recognizes deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of its assets and liabilities and the expected benefits of net operating loss carryforwards. The impact of changes in tax rates and laws on deferred taxes, if any, is applied during the years in which temporary differences are expected to be settled and is reflected in the financial statements in the period of enactment. The measurement of deferred tax assets is reduced, if necessary, if, based on weight of the evidence, it is more likely than not that some, or all, of the deferred tax assets will not be realized. At December 31, 2018 and 2017, the Company established a full valuation allowance against its deferred tax assets to an amount that is more likely than not to be realized. Recently Adopted Accounting Pronouncements Revenue Recognition In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09 (ASC 606), Revenue from Contracts with Customers . This ASU, as amended by ASU 2015-14, affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. ASU 2014-09 replaces most existing revenue recognition guidance in GAAP when it becomes effective. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the currently effective guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is effective for Exicure in the first quarter of 2018 and early adoption is permitted beginning in the first quarter of 2017. The Company adopted ASC 606 on a modified retrospective basis. See above “Revenue Recognition” for a discussion of the Company’s updated policies related to revenue recognition effective January 1, 2018. Impact of adoption of ASC 606 The Company adopted ASC 606 using the modified retrospective method. The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new guidance, the Company recorded reductions to both accumulated deficit and deferred revenue, current of $1,034 as of the date of adoption. As a result of the adoption of ASC 606: (i) there were no impacts to the totals of our cash flows from operating activities, cash flows from investing activities, or cash flows from financing activities in the accompanying consolidated statement of cash flows for the year ended December 31, 2018; (ii) there were no impacts to the balances of the accompanying consolidated balance sheet as of December 31, 2018, and (iii) total revenue, operating loss, and net loss were lower by $1,034 each in the accompanying consolidated statement of operations for the year ended December 31, 2018. Cash Flows In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . ASU 2016-15 addresses the classification of certain specific cash flow issues including debt prepayment or extinguishment costs, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of certain insurance claims and distributions received from equity method investees. ASU 2016-15 is effective for the Company in the first quarter of 2018 and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company adopted this guidance on January 1, 2018. The adoption of ASU 2016-15 did not have a material impact to the Company’s statement of cash flows. Stock-Based Compensation In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting . ASU 2017-09 clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. ASU 2017-09 will be applied prospectively to awards modified on or after the adoption date. ASU 2017-09 is effective for the Company for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted. The Company adopted this guidance on January 1, 2018. The adoption of ASU 2017-09 did not have a material impact to the Company’s financial statements. Recent Accounting Pronouncements Not Yet Adopted Leases In February 2016, FASB issued ASU 2016-02, Leases (Topic 842) , which requires lessees to recognize right-of-use assets and lease liabilities on the balance sheet. ASU 2016-02 is to be applied using a modified retrospective approach at the beginning of the earliest comparative period in the financial statements. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. ASU 2016-02 requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”), which allows entities to initially apply the new lease guidance at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We expect to adopt the new standard on January 1, 2019 and use the effective date as our date of initial application. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The Company is in the process of gathering a complete inventory of its lease contracts and evaluating the impact of the new guidance on its consolidated financial statements and related disclosures; however, management expects that the adoption of ASU 2016-02 will result in the recognition of a right-of-use asset and related liability associated with the Company’s non-cancelable operating lease arrangement for office and laboratory space that was executed in 2012 (see Note 12, Commitments and Contingencies ).

Purdue Collaboration

Purdue Collaboration	12 Months Ended
	Dec. 31, 2018
Research and Development [Abstract]
Purdue Collaboration	Purdue Collaboration On December 2, 2016, the Company entered into a research collaboration, option and license agreement with Purdue and referred to herein as the “Purdue Collaboration.” Purdue has the option to obtain from us the full worldwide development and commercial rights to AST-005 (the Company’s therapeutic candidate that targets tumor necrosis factor), an option to obtain three additional collaboration targets and a further option to obtain from us the full worldwide development and commercial rights to any therapeutic candidates developed targeting the three additional collaboration targets. In connection with the Purdue Collaboration, the Company received a non-refundable development fee of $10,000 . The Company is eligible to receive up to $776,500 upon successful completion of certain research, regulatory and commercial sales milestones. The research milestones are payable upon target identification and IND-enabling pre-clinical development, per program, with an aggregate total of up to $16,500 . The regulatory milestones are payable upon the initiation or completion of clinical trials, and regulatory approval in the United States and outside the United States, per program, with an aggregate total of up to $410,000 . The commercial sales milestones are payable upon achievement of specified aggregate product sales thresholds and total up to $350,000 . In the event a therapeutic candidate subject to the collaboration results in commercial sales, the Company is eligible to receive royalties ranging from the low single digits to a maximum of 10% on future net sales of such commercialized therapeutic candidates. In April 2018, Purdue notified the Company it had declined to exercise its option to develop AST-005 at that time and there are currently no active therapeutic candidates in development under the Purdue Collaboration. There can be no assurance that any research, regulatory and commercial sales milestones or royalties will be achieved as they are subject to highly significant risks and uncertainties, many of which are outside of our control. Prior to the adoption of ASC 606, the upfront payment of $10,000 was accounted for pursuant to ASC 605 and was recorded as deferred revenue and recognized on a ratable basis over the estimated performance period of the relevant research and development activities. On January 1, 2018, in connection with the adoption of ASC 606, the Company recorded the unamortized deferred revenue of $1,034 as an adjustment to the beginning balance of retained deficit at January 1, 2018. See Note 2, Significant Accounting Policies , for more information related to the adoption of ASC 606. The Company identified multiple performance obligations as part of the Purdue Collaboration agreement, including the upfront payment of $10,000 , discussed above, and the research and development services. The Company determined that the performance obligations should not be combined, the license should be recognized at the time the license is granted, and the research and development services should be recognized at the time the service is performed. The Purdue Collaboration agreement includes contingent promises related to specified research, development and regulatory milestones and sale-based milestones. Each contingent promise related to contingent and milestone payment is evaluated to determine whether it represents a material right. The Company recognizes any payment that is contingent upon the achievement of a substantive milestone entirely in the period in which it is determined that the revenue is not subject to a significant reversal. To date, the Company has not recognized any contingent payments in connection with the Purdue Collaboration agreement as revenue. During the year ended December 31, 2018, the Company recognized collaboration revenue of $118 which consisted entirely of research and development activities that will be reimbursed by Purdue and is presented on a gross basis in the accompanying statement of operations. During the year ended December 31, 2017, the Company recognized collaboration revenue of $9,719 which included $1,443 of research and development activities that was reimbursed by Purdue and is presented on a gross basis in the accompanying statement of operations.

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	12 Months Ended
	Dec. 31, 2018
Supplemental Balance Sheet Information [Abstract]
Supplemental Balance Sheet Information	Supplemental Balance Sheet Information Property and equipment, net December 31, 2018 2017 Scientific equipment $ 1,979 $ 1,797 Leasehold improvements 192 192 Furniture and fixtures 41 31 Computers and software 26 26 Construction in process 12 120 Property and equipment, gross 2,250 2,166 Less: accumulated depreciation (1,189 ) (849 ) Property and equipment, net $ 1,061 $ 1,317 Depreciation and amortization expense was $358 and $232 , for the years ended December 31, 2018 and 2017, respectively. Accrued expenses and other current liabilities December 31, 2018 2017 Accrued legal expenses $ 189 $ 251 Accrued payroll-related expenses 899 718 Accrued clinical, contract research and manufacturing costs 102 205 Other accrued expenses 353 99 Accrued expenses and other current liabilities $ 1,543 $ 1,273

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt On February 17, 2016, the Company closed a $10,000 loan facility, with an initial advance against this loan facility of $6,000 , with Hercules Technology Growth Capital (“Hercules”). The loan bears a floating interest rate equal to the greater of either (i) 9.95% or (ii) the sum of 9.95% plus the United States prime rate minus 3.50% . Total proceeds net of fees and issuance costs were $5,839 . Fees and issuance costs of $161 , as well as fees of $231 that are payable to the lender at maturity, are recorded as a reduction in the carrying amount of long-term debt on our balance sheet and will be amortized to interest expense through the maturity date of September 1, 2019 using the effective interest method. Interest amounts were payable monthly beginning on March 1, 2016 through the maturity date of September 1, 2019 . Initially, principal amounts were payable monthly beginning on April 1, 2017 through the maturity date. In 2016, the Company met certain terms in the loan agreement so that principal amounts became payable monthly beginning on July 1, 2017. On January 15, 2018, the Company and Hercules amended its loan agreement so that amortization payments due for the thirteen (13) consecutive months commencing on December 1, 2017 through and including December 1, 2018 were deferred. Commencing on January 1, 2019, and continuing on the first business day of each month thereafter, the loan, including the deferred payments, was to begin amortizing in equal monthly installments of principal and interest based upon an amortization schedule equal to eighteen (18) consecutive months. Any remaining obligations under the loan agreement and other loan documents were due and payable on the maturity date on September 1, 2019. On December 28, 2018, the Company and Hercules further amended its loan agreement so that interest amounts are payable on the first day of each business month and any remaining obligations under the loan agreement and other loan documents are due and payable on the maturity date on September 1, 2019. The loan is collateralized by a security interest in all tangible assets. In addition, the Company is subject to certain financial reporting requirements and certain negative covenants requiring lender consent. In connection with the February 2016 Hercules loan, Hercules also had the right to purchase 80,000 shares of Series C preferred stock at $3.00 per share under the terms of a warrant agreement with the Company. The preferred stock warrant liability was recorded at fair value at the date of issuance of February 17, 2016 in the amount of $134 and recorded as a reduction in the carrying amount of long-term debt on our balance sheet. This discount of $134 will be amortized to interest expense through the loan maturity date of September 1, 2019 using the effective interest method. The Company estimated the fair value of the preferred stock warrant liability at the end of each reporting period using the Black-Scholes model and recorded any changes in fair value to other income (expense), net on its statement of operations. See Note 10, Fair Value Measurements , for more information on the fair value of the preferred stock warrant liability. The warrant agreement to purchase shares of preferred stock was terminated on September 26, 2017 in connection with the Merger. At December 31, 2018 and 2017, the aggregate carrying value of the current and noncurrent portion of long-term debt is $4,925 and $4,855 , respectively. At December 31, 2018, the principal maturities of the long-term debt were as follows: December 31, 2018 2019 $ — 2020 4,999 Principal balance outstanding 4,999 less: unamortized discount (69 ) less: unamortized debt issuance costs (5 ) Long-term debt 4,925 Current portion — Noncurrent portion $ 4,925 The Company paid interest on debt of $572 and $611 during the years ended December 31, 2018 and 2017, respectively. Refer to Note 15, Subsequent Events , for more information on our loan agreement with Hercules.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock As of December 31, 2018 and 2017, the Company had 10,000,000 shares of preferred stock, par value $0.0001 authorized and no shares issued and outstanding. Common Stock As of December 31, 2018 and 2017, the Company had authorized 200,000,000 shares of common stock, par value $0.0001 . As of December 31, 2018, the Company had 44,358,000 shares issued and outstanding. As of December 31, 2017, the Company had 39,300,823 shares issued and outstanding. The holders of shares of the Company’s common stock are entitled to one vote per share on all matters to be voted upon by Exicure stockholders and there are no cumulative rights. Subject to preferences that may be applicable to any outstanding preferred stock, the holders of shares of the Company’s common stock are entitled to receive ratably any dividends that may be declared from time to time by Exicure’s board of directors (the “Board”) out of funds legally available for that purpose. In the event of the Company’s liquidation, dissolution or winding up, the holders of shares of Exicure common stock are entitled to share ratably in all assets remaining after payment of liabilities, subject to prior distribution rights of preferred stock then outstanding. Exicure common stock has no preemptive or conversion rights or other subscription rights. There are no redemption or sinking fund provisions applicable to Exicure common stock. The outstanding shares of Exicure common stock are fully paid and non-assessable. August 2018 Private Placement On August 22, 2018, the Company entered into subscription agreements with several accredited investors, pursuant to which it agreed to issue and sell a total of 4,889,217 shares of the Company’s common stock, at a purchase price of $4.50 per share, resulting in approximately $22,001 in gross proceeds to the Company (the “August 2018 Private Placement”). The aggregate net proceeds from the August 2018 Private Placement (after deducting placement agent fees and expenses of the offering of $1,931 ) were $20,070 . The Company also entered into a registration rights agreement with the investors in the August 2018 Private Placement, which required it to file a “resale” registration statement with the SEC covering the shares issued in the August 2018 Private Placement within 30 calendar days from the final closing of the August 2018 Private Placement Offering. The Company filed and caused to become effective a registration statement with the SEC on October 5, 2018 registering the resale of 5,034,683 shares of our common stock, consisting of (i) 4,889,217 shares that were privately issued through the August 2018 Private Placement and (ii) 145,466 shares that were privately issued on February 1, 2018 in connection with consulting services. In connection with the closing of the August 2018 Private Placement, the placement agents received an aggregate of $1,680 in cash placement fees, and the Company reimbursed up to $87 of expenses incurred by the placement agents in connection with this closing of the August 2018 Private Placement. 2017 Private Placement On September 26, 2017, following the Effective Time of the Merger, the Company sold 6,767,360 shares of Exicure, Inc. common stock pursuant to an initial closing of a private placement offering (the “Offering”) for up to 13,333,333 shares of Exicure, Inc. common stock at a purchase price of $3.00 per share (the “Offering Price”). The aggregate net proceeds from the initial closing of the Offering (after deducting placement agent fees and expenses of the initial offering of $3,037 ) were $17,235 . On October 27, 2017 and November 2, 2017, Exicure entered into subscription agreements (the “Subscription Agreements”) with several accredited investors (the “Investors”) pursuant to which the Company agreed to issue and sell a total of 3,736,836 shares of the Company’s common stock, par value $0.0001 per share (the “Shares”) resulting in approximately $11,211 in gross proceeds to the Company. These shares were issued in Subsequent Closings of the Offering for up to 13,333,333 shares of common stock (the “Maximum Amount”) at a purchase price of $3.00 per share (the “Sale Price”). The Company has sold a total of 10,504,196 shares of common stock for a total of approximately $31,513 in connection with all closings of the Offering (before deducting placement agent fees and expenses which are estimated at $3,966 ) (the “2017 Private Placement”). Placement Agents have received an aggregate of $1,968 in cash placement fees and have received warrants to purchase an aggregate of 413,320 shares of Exicure common stock (the “Warrants”) in connection with the 2017 Private Placement. The Warrants expire on March 27, 2021, have an exercise price of $3.00 per share, and have been issued on the same terms in all closings of the Offering. The warrants to purchase common stock are classified as a liability and presented as a dividend that offsets the gross proceeds of the 2017 Private Placement within the accompanying consolidated statement of changes in stockholders’ equity. The common stock warrant liability will be remeasured each period at fair value. See Note 10, Fair Value Measurements for more information on the common stock warrant liability. The Placement Agents also received 50,000 shares of Exicure common stock in connection with all closings of the Offering. Subject to certain customary exceptions, investors in the 2017 Private Placement have anti-dilution protection with respect to the shares of common stock sold in the Offering such that if within eighteen (18) months after the initial closing of the Offering the Company issues certain additional shares of common stock or common stock equivalents for a consideration per share less than the Offering Price (the “Lower Price”), each such investor will be entitled to receive from the Company additional shares of common stock in an amount such that, when added to the number of shares of common stock initially purchased by such investor in the Offering and still held of record and beneficially owned by such investor at the time of the dilutive issuance (the “Held Shares”), will equal the number of shares of common stock that such investor’s aggregate purchase price for the Held Shares would have purchased at the Lower Price. Either (i) holders of a majority of the then Held Shares or (ii) a representative of the holders of the then Held Shares, which representative shall be appointed by the three investors who then hold the largest number of Held Shares, may waive the anti-dilution rights of all Offering investors with respect to a particular issuance by the Company. This price-based anti-dilution protection automatically terminated on August 22, 2018 in connection with the August 2018 Private Placement. The 2017 Private Placement was exempt from registration under Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”), and Rule 506 of Regulation D promulgated by the SEC. The common stock in the Offering was sold to “accredited investors,” as defined in Regulation D, and was conducted on a “reasonable best efforts” basis. In connection with the Merger and the 2017 Private Placement, the Company entered into a Registration Rights Agreement, pursuant to which the Company has agreed that promptly, but no later than 60 calendar days from the final closing of the Offering, the Company will file a registration statement with the SEC, or the Registration Statement. Each Investor in the Subsequent Closing also entered into the same registration rights agreement signed by investors in the initial closing of the Offering, which requires that the Company file a “resale” registration statement with the SEC covering the shares of common stock and warrants issued in the 2017 Private Placement, certain other shares of common stock issued in connection with the Company’s recently closed reverse merger, and shares held by the Company’s pre-merger stockholders, within 60 calendar days from the final closing of the Offering. The Company filed and caused to become effective a registration statement with the SEC on February 6, 2018 registering the resale of 39,714,143 shares of our common stock issued in connection with the Reverse Merger and the 2017 Private Placement. Common Stock Warrants As discussed above, in connection with the 2017 Private Placement, placement agents received warrants to purchase an aggregate of 413,320 shares of Exicure common stock in connection with all closings of the 2017 Private Placement. The Warrants expire on March 27, 2021, have an exercise price of $3.00 per share, and have been issued on the same terms in all closings of the 2017 Private Placement. The Warrants are classified as a liability. The common stock warrant liability is remeasured each period at fair value. As of December 31, 2018, Warrants to purchase 413,320 shares of common stock remain outstanding. See Note 10, Fair Value Measurements for more information on the fair value of the common stock warrant liability. The Merger On September 26, 2017, in connection with the Merger, each share of Exicure OpCo common and preferred stock (other than shares of Exicure OpCo’s Series C preferred stock) issued and outstanding immediately prior to the closing of the Merger was converted into 0.49649 shares of Max-1’s common stock, and each share of Exicure OpCo’s Series C preferred stock issued and outstanding immediately prior to the closing of the Merger was converted into 0.7666652 shares of Max-1’s common stock. As a result, an aggregate of 26,666,627 shares of the Max-1’s common stock were issued to the holders of Exicure OpCo’s capital stock, which is incremental to the 2,080,000 shares of Max-1’s common stock that were outstanding immediately prior to the Merger. In addition, pursuant to the Merger Agreement options to purchase 7,414,115 shares of Exicure OpCo common stock issued and outstanding immediately prior to the closing of the Merger were assumed by Max-1 and converted into options to purchase 3,680,997 shares of the Max-1’s common stock. Other - Prior to the Merger Series C Preferred Stock On January 11, 2016, the Company sold 149,999 shares of its Series C preferred stock at a price of $3.00 per share. Total gross proceeds raised thereby were $450 . Net proceeds after associated costs and expenses of $6 were $444 . Liquidation preference . The Series C preferred stock were senior to the Class A and Class B preferred stock and common stock in rights and privileges as established in the Exicure OpCo Operating Agreement. Principal among the rights of Class C preferred stock was the creation of the Class C liquidation preference whereby, in the event of a liquidation event (i.e., a liquidation, dissolution or winding up of the Company or a sale of the Company), the Class C preferred stock holders were entitled to receive 1.5 times the aggregate cash contribution of all holders of Class C preferred units/stock.

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-Based Compensation	Equity-Based Compensation On September 22, 2017, the Board adopted and Exicure’s stockholders approved the Exicure, Inc. 2017 Equity Incentive Plan (the “2017 Plan”), which became effective on November 15, 2017. The 2017 Plan provides for the issuance of incentive awards of up to 5,842,525 shares of Exicure common stock, which includes 2,169,905 shares of Exicure common stock to be issued to officers, employees, consultants and directors, plus a number of shares not to exceed 3,683,817 that are subject to issued and outstanding awards under the Exicure OpCo 2015 Equity Incentive Plan (the “2015 Plan”) and were assumed in the Merger. Awards that may be awarded under the 2017 Plan include non-qualified and incentive stock options, stock appreciation rights, bonus shares, restricted stock, restricted stock units, performance units and cash-based awards. The 2017 Plan also provides that the number of shares reserved for issuance thereunder will be increased annually on the first day of each year beginning in 2020 by the least of 4,600,000 shares, five percent ( 5% ) of the shares of Exicure common stock outstanding on the last day of the immediately preceding year, or a lesser number of shares as determined by the Company’s compensation committee. No future awards will be made under the 2015 Plan upon the effectiveness of the 2017 Plan. As of December 31, 2018, the aggregate number of common stock options available for grant under the 2017 Equity Incentive Plan was 928,443 . The common stock options are contingent on the participants’ continued employment or provision of non-employee services and are subject to forfeiture if employment or continued service terminates for any reason. The initial stock option grant to an employee, director or consultant vests 25% on the first 12-month anniversary of the grant date and vests 1/48th monthly thereafter until fully vested at the end of 48 months . Subsequent stock option grants vest 1/48th monthly until fully vested at the end of 48 months . The term of common stock option grants is ten years unless terminated earlier as described above. Equity-based compensation expense is classified in the statements of operations as follows: Year Ended December 31, 2018 2017 Research and development expense $ 485 $ 172 General and administrative expense 1,324 1,290 $ 1,809 $ 1,462 Unamortized equity-based compensation expense at December 31, 2018 was $3,172 , which is expected to be amortized over a weighted-average period of 2.5 years . The Company utilizes the Black-Scholes option-pricing model to determine the fair value of common stock option grants. The Black-Scholes option-pricing model was developed for use in estimating the fair value of traded options that have no vesting restrictions and are fully transferable. The model also requires the input of highly subjective assumptions. In addition to an assumption on the expected term of the option grants as discussed below, application of the Black-Scholes model requires additional inputs for which we have assumed the values described in the table below: Year Ended December 31, 2018 2017 Expected term 5.3 to 6.0 years 5.3 to 6.5 years Risk-free interest rate 2.72% to 2.87%; weighted avg. 2.78% 1.97% to 2.17%; weighted avg. 2.07% Expected volatility 78.1% to 82.4%; weighted avg. 80.6% 80.8% to 83.1%; weighted avg. 81.0% Forfeiture rate 5 % 5 % Expected dividend yield — % — % The expected term is based upon the “simplified method” as described in Staff Accounting Bulletin Topic 14.D.2. Currently, the Company does not have sufficient experience to provide a reasonable estimate of an expected term of its common stock options. The Company will continue to use the “simplified method” until there is sufficient experience to provide a more reasonable estimate in conformance with ASC 718-10-30-25 through 30-26. The risk-free interest rate assumptions were based on the U.S. Treasury bond rate appropriate for the expected term in effect at the time of grant. The expected volatility is based on calculated enterprise value volatilities for publicly traded companies in the same industry and general stage of development. The estimated forfeiture rates were based on historical experience for similar classes of employees. The dividend yield was based on expected dividends at the time of grant. The fair value of the underlying common stock and the exercise price for the common stock options granted during the years ended December 31, 2018 and 2017 are summarized in the table below: Common Stock Options Granted During Period Ended: Fair Value of Underlying Common Stock Exercise Price of Common Stock Option Year ended December 31, 2018 $3.00 to $5.82; weighted avg. $3.45 $3.00 to $5.82; weighted avg. $3.45 Year ended December 31, 2017 $4.21 $4.21 The weighted-average grant date fair value of common stock options granted in the years ended December 31, 2018 and 2017 was $2.40 and $2.92 per common stock option, respectively. A summary of common stock option activity as of the periods indicated is as follows: Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value (thousands) Outstanding - December 31, 2017 3,672,620 $ 1.79 7.5 $ 5,221 Granted 1,277,744 3.45 Exercised (22,494 ) 1.81 Forfeited (36,282 ) 2.29 Outstanding - December 31, 2018 4,891,588 $ 2.22 7.3 $ 7,330 Exercisable - December 31, 2018 3,238,798 $ 1.70 6.7 $ 6,352 Vested and Expected to Vest - December 31, 2018 4,799,984 $ 2.20 7.3 $ 7,287 The aggregate intrinsic value of common stock options exercised during the years ended December 31, 2018 and 2017 was $44 and $202 , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Pretax loss before income taxes was $22,413 and $11,011 for the years ended December 31, 2018 and 2017, respectively, which consists entirely of losses in the U.S. and resulted in no provision for income tax expense during the years then ended. The differences between income taxes computed using the U.S. federal income tax rate and the provision for income taxes are as follows: Year Ended December 31, 2018 2017 Federal income tax expense at statutory rate $ (4,707 ) 21.0 % $ (4,093 ) 34.0 % State income tax expense at statutory rate (1,595 ) 7.1 (610 ) 5.1 Permanent differences 243 (1.1 ) (125 ) 1.0 Impact of Tax Reform Act — — 3,760 (31.2 ) Other — — (10 ) 0.1 Change in valuation allowance 6,059 (27.0 ) 1,078 (9.0 ) $ — — % $ — — % The Company’s effective income tax rate for the years ended December 31, 2018 and 2017 is 0% because the Company has generated tax losses and has provided a full valuation allowance against its deferred tax assets to an amount that is more likely than not to be realized. The significant components of the Company’s net deferred tax assets are as follows: December 31, 2018 2017 Deferred Tax Assets Net operating losses $ 14,827 $ 8,748 Intangibles 187 205 Accrued expenses 271 198 Equity-based compensation 796 728 Deferred revenue — 295 Other 204 — Less: Valuation allowance (16,225 ) (10,166 ) Total deferred tax assets 60 8 Deferred Tax Liabilities Fixed assets and other (60 ) (8 ) Total deferred tax liabilities (60 ) (8 ) Deferred taxes, net $ — $ — The Company has recorded a full valuation allowance against its deferred tax assets to an amount that is more likely than not to be realized at December 31, 2018 and 2017. This determination is based on significant negative evidence, including: • Cumulative losses: The Company has been in a significant cumulative loss position since its inception in 2011. • Projected realization of net operating loss carry forward amounts: Projections of future pre-tax book loss and taxable losses based on the Company’s recent actual performance and current industry data indicate it is more likely than not that the benefits will not be recognized. On December 22, 2017, the President of the United States signed into law the Tax Reform Act. The legislation significantly changes U.S. tax law by, among other things, lowering corporate income tax rates, implementing a modified territorial tax system and imposing a repatriation tax on deemed repatriated earnings of foreign subsidiaries. The Tax Reform Act permanently reduces the U.S. corporate income tax rate from a maximum of 35% to a flat 21% rate, effective January 1, 2018. The Company’s U.S. deferred tax assets, net of deferred tax liabilities, were remeasured at December 31, 2017 and reduced by $3,760 , entirely offset by a valuation allowance reduction. As a result, the remeasurement of the Company’s deferred tax assets, net of deferred tax liabilities, including the valuation allowance, did not impact the Company’s income tax expense or net loss. At December 31, 2018, the Company had a federal net operating loss carryforward of $52,629 which will begin to expire in 2035. The Company has $50,294 of state net operating loss carryforwards which will begin to expire in 2027. At December 31, 2018 and 2017, the Company had no unrecognized tax benefits. The Company’s estimate of the potential outcome of any uncertain tax position is subject to management’s assessment of relevant risks, facts and circumstances existing at that time. The Company evaluates uncertain tax positions to determine if it is more-likely-than-not that they would be sustained upon examination. The Company recognizes interest and penalties related to unrecognized tax benefits in the provision for income taxes. The Company is subject to taxation in the U.S. and various state jurisdictions. The Company remains subject to examination by U.S. federal and state tax authorities for the years 2015 through 2018. There are no pending examinations in any jurisdiction.

Loss Per Common Share

Loss Per Common Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Loss Per Common Share	Loss Per Common Share Basic loss per common share is calculated by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted loss per common share is calculated using the treasury share method by giving effect to all potentially dilutive securities that were outstanding. Potentially dilutive options and warrants to purchase common stock that were outstanding during the periods presented were excluded from the diluted loss per share calculation because such shares had an anti-dilutive effect due to the net loss reported in those periods. Therefore, basic and diluted loss per common share is the same for each of the years ended December 31, 2018 and 2017. The following is the computation of loss per common share for the years ended December 31, 2018 and 2017: Year Ended December 31, 2018 2017 Net loss $ (22,413 ) $ (11,011 ) Weighted-average basic and diluted common shares outstanding 41,189,177 10,119,569 Loss per share - basic and diluted $ (0.54 ) $ (1.09 ) The outstanding securities presented below were excluded from the calculation of net loss per common share, because such securities would have been anti-dilutive due to the Company’s net loss per share during the periods ending on the dates presented: December 31, 2018 2017 Options to purchase common stock 4,891,588 3,672,620 Warrants to purchase common stock 413,320 413,320

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements ASC Topic 820, Fair Value Measurement, establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, as follows: Level 1 Inputs - unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date; Level 2 Inputs - other than quoted prices included in Level 1 inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability; and Level 3 Inputs - unobservable inputs for the asset or liability used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at measurement date. The Company uses the market approach and Level 1 inputs to value its cash equivalents. The Company’s long-term debt bore interest at the prevailing market rates for instruments with similar characteristics and, accordingly, the carrying value for this instrument also approximates its fair value and the financial measurement is also classified within Level 2 of the fair value hierarchy. The Company’s common stock warrant liability (refer to Note 6, Stockholders’ Equity , for more information) and preferred stock warrant liability (terminated on September 26, 2017 in connection with the Merger; see Note 5, Debt , for more information) are classified within Level 3 of the fair value hierarchy. The fair values of the common stock warrant liability and preferred stock warrant liability were determined using the Black-Scholes option-pricing model. The fair value of the common stock warrant liability is based significantly on the fair value of the Company’s common stock. At the date of issuance, the common stock warrant liability was determined using the following weighted-average assumptions: expected term of 2.0 years , risk-free interest rate of 1.53% , expected volatility of 78.97% , and no expected dividends. The fair value of the preferred stock warrant liability was based significantly on the fair value of the Series C preferred stock, which was developed using unobservable inputs, which are classified within Level 3. At the date of issuance, the preferred stock warrant liability was determined using the following assumptions: expected term of 5.0 years , risk-free interest rate of 1.26% , expected volatility of 62.99% , and no expected dividends. In connection with the Merger, the warrants to purchase preferred stock were terminated and therefore the related liability was reduced to zero during 2017. The following weighted-average assumptions were used to estimate the fair value of the common stock warrant liability at December 31, 2018: December 31, 2018 Expected term 2.3 Risk-free interest rate 2.46 % Expected volatility 86.74 % Expected dividend yield — % A 10% change in the estimate of expected volatility at December 31, 2018 would increase or decrease the fair value of the common stock warrant liability in the amount of $53 . A 10% change in the estimate of fair value of the common stock at December 31, 2018 would increase or decrease the fair value of the common stock warrant liability in the amount of $118 . The following is a reconciliation of the Company’s liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3) for the years ended December 31, 2018 and 2017: Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Preferred Stock Warrant Liability Common Stock Warrant Liability Total Balance at January 1, 2017 $ 201 $ — $ 201 Additions — 536 536 Gain included in other income (expense), net (201 ) (13 ) (214 ) Balance at December 31, 2017 $ — $ 523 $ 523 Loss included in other income (expense), net — 274 274 Balance at December 31, 2018 $ — $ 797 $ 797

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Defined Contribution Plan	Defined Contribution Plan Exicure maintains a defined contribution savings plan for the benefit of its employees. During 2018, Exicure began contributing to the defined contribution plan. Company contributions are determined under various formulas. The expense recognized for this plan was $107 for the year ended December 31, 2018.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company conducts all operations in a facility under an operating lease which commenced in March 2012 and was originally scheduled to end in February 2015. The lease was extended for an additional six years through February 2021 during the first quarter of 2014 and includes a renewal option. During the second quarter of 2016, the Company amended the lease agreement to include additional space to be used primarily for administrative functions effective in May 2016. Lease payments include a fixed payment amount as well as contingent payments related to a proportionate share of operating and real estate expenses. At the inception of the lease, the lessor paid for leasehold improvements totaling $52 which has been capitalized and is being amortized over the lease term. The fixed payment amounts, including those in connection with the amended lease agreement in the second quarter of 2016, increase over the term of the lease but rent expense is recognized on a straight-line basis resulting in the recognition of deferred rent liability of $39 and $48 as of December 31, 2018 and December 31, 2017, respectively, calculated on the basis of the extended lease agreement. Rent expense consisted of the following: Years Ended December 31, 2018 2017 Straight-line rent expense $ 332 $ 332 Contingent rent expense 298 281 Total rent expense $ 630 $ 613 Future minimum lease payments as of December 31, 2018 are as follows: Years Ending December 31, Operating Leases 2019 347 2020 353 2021 59 Thereafter — Total $ 759 Northwestern University License Agreements On December 12, 2011, (1) AuraSense, LLC assigned to the Company all of its worldwide rights and interests under AuraSense, LLC’s 2009 license agreement with Northwestern University (“NU”) in the field of the use of nanoparticles, nanotechnology, microtechnology or nanomaterial-based constructs as therapeutics or accompanying therapeutics as a means of delivery, but expressly excluding diagnostics (the “assigned field”); (2) in accordance with the terms and conditions of this assignment, the Company assumed all liabilities and obligations of AuraSense, LLC as set forth in its license agreement in the assigned field; and (3) in order to secure this assignment and the patent rights from NU, the Company agreed (i) to pay NU an annual license fee, which may be credited against any royalties due to NU in the same year, (ii) to reimburse NU for expenses associated with the prosecution and maintenance of the license patent rights, (iii) to pay NU royalties based on any net revenue generated by the Company’s sale or transfer of any licensed product, and (iv) to pay NU, in the event the Company grants a sublicense under the licensed patent rights, the greater of a percentage of all sublicensee royalties or a percentage of any net revenue generated by a sublicensee’s sale or transfer of any licensed product. In August 2015, we entered into a restated license agreement with NU (the “restated license agreement”). In February 2016, we obtained exclusive license as to NU’s rights in certain SNA technology we jointly own with NU. Our license to NU’s rights is limited to the assigned field, however we have no such limitation as to our own rights in this jointly owned technology. In June 2016, we entered into an exclusive license with NU to obtain worldwide rights to certain inhibitors of glucosylceramide synthase and their use in wound healing in diabetes. Our rights and obligations in these 2016 agreements are substantially the same as in the restated license agreement from August 2015 (collectively referred to as “the Northwestern University License Agreements”). As of December 31, 2018, the Company has paid to NU an aggregate of $3,864 in consideration of each of the obligations described above.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions Since its inception in 2011, the Company has shared facilities, certain staff members and certain operating expenses with AuraSense, LLC, our former parent and largest stockholder. On an infrequent basis, the Company also pays certain expenses directly on behalf of AuraSense, LLC which are related to AuraSense, LLC’s grants, and AuraSense, LLC sometimes pays expenses directly on behalf of the Company. These costs are summarized and directly billed between the Company and AuraSense, LLC on a quarterly basis. In addition, certain expense and administrative activities are shared between the Company and AuraSense, LLC. Effective January 1, 2016, the Company and AuraSense, LLC amended its shared services agreement to simplify the billing arrangement. Under the amended shared services agreement, the Company bills AuraSense, LLC $8 per quarter for indirect costs incurred by the Company plus a specified rate for hours worked by Company scientists on projects directly related to AuraSense, LLC. The amended shared services arrangement continues to require direct non-labor expenses incurred by the Company to be billed to AuraSense, LLC. Effective January 1, 2017, the Company and AuraSense, LLC further amended its shared services agreement so that the quarterly fee related to administrative activities billed by the Company to AuraSense, LLC be reduced to $3 per quarter. This decrease was to reflect the current and expected future reduction in administrative activities to be provided by the Company to AuraSense, LLC. The amounts due from AuraSense, LLC in connection with the above mentioned activities were $10 and $17 at December 31, 2018 and 2017, respectively. The following is a summary of amounts billed to AuraSense, LLC and recognized in the accompanying consolidated statement of operations in connection with the above mentioned activities: For the Years Ended December 31, 2018 2017 Quarterly fee for indirect costs $ 12 $ 12 Direct costs of AuraSense LLC paid by the Company 26 5 $ 38 $ 17 The Company received consulting services from, and paid fees to, one of its co-founders who is not an employee but serves as a member of the Board. The Company paid $100 in each of the years ended December 31, 2018 and 2017 in connection with these consulting services and these amounts are recognized as an expense in the accompanying consolidated statement of operations.

Quarterly Financial Data (Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	Quarterly Financial Data (Unaudited) Selected quarterly financial data for the years ended December 31, 2018 and 2017 are as follows: 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Revenue (1) 36 19 57 6 Net loss (1)(2) (5,509 ) (6,825 ) (5,324 ) (4,755 ) Basic and diluted loss per common share (3) $ (0.14 ) $ (0.17 ) $ (0.13 ) $ (0.11 ) 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Revenue 2,432 2,695 2,497 2,095 Net loss (2,652 ) (2,984 ) (1,932 ) (3,443 ) Basic and diluted loss per common share (3) $ (15.62 ) $ (15.70 ) $ (1.12 ) $ (0.09 ) ___________ (1) - As discussed in Note 2, Significant Accounting Policies - Recently Adopted Accounting Pronouncements , the Company adopted ASC 606 on a modified retrospective basis effective January 1, 2018. As a result of the adoption of ASC 606, total revenue and net loss were lower by $1,034 each in the three months ended March 31, 2018. (2) - Net loss includes a non-cash unrealized (loss) gain related to the fair value adjustment of the common stock warrant liability of ($128) , ($915) , $581 , and $186 in the three months ended March 31, 2018, June 30, 2018, September 30, 2018, and December 31, 2018, respectively. (3) - As discussed in Note 1, Description of Business and Basis of Presentation - The Merger , shares of preferred stock issued and outstanding immediately prior to the closing of the Merger were converted into an aggregate of 26,476,543 shares of common stock. As such, these shares of common stock are included in the computation of basic and diluted loss per common share beginning with September 26, 2017 and excluded from the computation of basic and diluted loss per common share for dates prior to September 26, 2017.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events which may require adjustment to or disclosure in the accompanying consolidated financial statements and has concluded that, other than the Hercules loan amendment and license agreement with Dermelix disclosed below, there are no subsequent events or transactions that occurred subsequent to the balance sheet date that would require recognition or disclosure in the accompanying consolidated financial statements. Hercules loan amendment On March 8, 2019, the Company and Hercules amended its loan agreement so that the maturity date of its loan agreement is extended to March 1, 2020 and amortization payments are deferred to, and payable at, the new maturity date of March 1, 2020. Dermelix license agreement On February 17, 2019, Exicure entered into a License and Development Agreement (the “Dermelix License Agreement”) with Dermelix, LLC d/b/a Dermelix Biotherapeutics (“Dermelix”). Pursuant to the Dermelix License Agreement, the Company granted to Dermelix exclusive, worldwide royalty-bearing license rights to, develop, manufacture, have manufactured, use and commercialize the Company’s spherical nucleic acid (“SNA”) technology for the treatment of Netherton Syndrome (“NS”) and, at Dermelix’s option, up to five additional specified orphan diseases that are within the dermatology field. Upon written notice to the Company, Dermelix may exercise its option at any time following the effective date of the Dermelix License Agreement until the date that is six (6) years from the date that the first collaboration SNA therapeutic achieves first dosing in humans in a Phase 1 clinical trial for NS. Dermelix will initially seek to develop a targeted therapy for the treatment of NS. Under the terms of the Dermelix License Agreement, the Company will be responsible for conducting the early stage development for each indication up to IND enabling toxicology studies. Dermelix will assume subsequent development, commercial activities and financial responsibility for such indications. Dermelix will pay the costs and expenses of development and commercialization of any licensed products under the Dermelix License Agreement, including the Company’s expenses incurred in connection with development activities and in accordance with the development budget. Under the terms of the Dermerlix License Agreement, Exicure received an upfront payment of $1,000 , to be applied against the initial $1,000 of the Company’s development expenses. If Dermelix exercises any of its option rights for additional indications, Dermelix will pay an option exercise fee equal to $1,000 for each exercised option (each, an “Option Exercise Fee”). Any Option Exercise Fee will be applied against the Company’s development expenses with respect to the particular indication for which the option was exercised. Pursuant to the Dermelix License Agreement, the Company shall have the right to pursue the development and commercialization of SNA technology for the treatment of orphan diseases which are neither NS nor one of the additional specified orphan diseases selected by Dermelix pursuant to its option rights. If the Company commences development activities of SNA technology for the treatment of such an orphan disease, the Company will notify Dermelix in writing of such development and Dermelix will have thirty (30) days following receipt of such notice to use one of its remaining option rights on such orphan disease. If Dermelix does not use one of its remaining option rights on such orphan disease, or has no option rights remaining, then the Company will have no further obligations to Dermelix with respect to the development of SNA therapeutics for such orphan disease and shall be free to continue commercialization and development activities with respect thereto. For each of NS as well as any additional licensed product for which Dermelix exercises one of its options, the Company shall be eligible to receive additional cash payments totaling up to $13,500 upon achievement of certain development and regulatory milestones and up to $152,500 upon achievement of certain sales milestones. In addition, the Company will receive low double-digit royalties on annual net sales for such licensed products. The Dermelix License Agreement will remain in effect, unless terminated earlier, until the last-to-expire royalty term under the Dermelix License Agreement. Each party has the right to terminate the Dermelix License Agreement for the other party’s material breach of its obligations or representations and warranties under the Dermelix License Agreement, subject to cure rights. Additionally, Dermelix may terminate the Dermelix License Agreement in its sole discretion and in its entirety with specified prior written notice. The Company may also terminate the Dermelix License Agreement in part with respect to a particular indication if Dermelix fails to pay a development milestone payment following non-achievement of a development milestone. Upon termination of the term with respect to a particular licensed product, the license for such product will convert to a fully-paid, royalty-free, irrevocable, perpetual, exclusive and sublicensable license. Upon termination of the Dermelix License Agreement by Dermelix for convenience, by the Company following non-achievement of a development milestone, or by either party for the other’s breach or bankruptcy, all licenses granted by the Company to Dermelix will terminate. The Dermelix License Agreement includes customary representations and warranties on behalf of both the Company and Dermelix, including representations and operative provisions as to the licensed intellectual property. The Dermelix License Agreement also provides for certain mutual indemnities for breaches of representations, warranties and covenants. Upon a change of control of the Company, Dermelix will have 90 days to exercise any of its remaining options for additional indications, and any options that are not exercised within such 90 -day period will lapse. Either party may assign the Dermelix License Agreement or delegate its obligations to an affiliate or to a successor without the consent of the other party.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of presentation	Basis of Presentation The accompanying consolidated financial statements as of December 31, 2018 and 2017, and for the years then ended, have been presented in conformity with generally accepted accounting principles in the United States (“GAAP”).
Principles of consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Exicure, Inc. and its 100% owned subsidiary, Exicure Operating Company. All intercompany transactions and accounts are eliminated in consolidation.
Use of estimates	Use of Estimates The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and 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. Management bases its estimates on certain assumptions which it believes are reasonable in the circumstance and while actual results could differ from those estimates, management does not believe that any change in those assumptions in the near term would have a significant effect on the Company’s financial position, results of operations or cash flows. Actual results in future periods could differ from those estimates.
Cash and cash equivalents	Cash and cash equivalents The Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents.
Accounts receivable and unbilled revenue receivable	Accounts receivable and unbilled revenue receivable Accounts receivable and unbilled revenue receivable consist of reimbursement for research and development activities in connection with the research collaboration, license, and option agreement with Purdue Pharma L.P. (“Purdue”). The Company’s management believes these receivables are fully collectible.
Fair value of financial instruments	Fair value of financial instruments The carrying amounts of financial instruments, which include cash and cash equivalents and accounts payable, approximate their respective fair values due to the relatively short-term nature of these instruments. Management believes that the Company’s long-term debt bears interest at the prevailing market rate for instruments with similar characteristics and, accordingly, the carrying value of long-term debt also approximates their fair value.
Concentrations of credit risk and other risks and uncertainties	Concentrations of credit risk and other risks and uncertainties Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. As of December 31, 2018 and 2017, the Company had cash and cash equivalents of $26,268 and $25,764 , respectively. The cash balances at each respective period were maintained at two institutions. These deposits exceed federally insured limits. During the years ended December 31, 2018 and 2017, one counterparty accounted for all of the Company’s revenue. The Company is currently not profitable and no assurance can be provided that it will ever be profitable. The Company’s research and development activities have required significant investment since inception and operations are expected to continue to require cash investment in excess of its revenues. See also Note 1, Description of Business and Basis of Presentation—Going Concern , for more information. The Company is subject to risks common in therapeutic development including, but not limited to, therapeutic candidates that appear promising in the early phases of development often fail because they prove to be inefficacious or unsafe, clinical trial results are unsuccessful, regulatory bodies may not approve the therapeutic or the therapeutic may not be economical in production or distribution. The Company is also subject to risks common to biotechnology firms including, but not limited to new and disruptive technological innovations, dependence on key personnel, protection of proprietary technology, the validity of and continued access to its owned and licensed intellectual property, limitations on the supply of critical materials, compliance with governmental regulations and market acceptance.
Property and equipment	Property and equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the various classes of property and equipment, which range from three to seven years. Leasehold improvements are amortized using the straight-line method over the shorter of the remaining terms of the respective leases or the estimated lives of the assets. Depreciation begins at the time the asset is placed in service. Property and equipment are reviewed for impairment at least annually or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable.
Common stock warrant liability	Common stock warrant liability Freestanding warrants related to shares that are redeemable, contingently redeemable, or for purchases of common stock that are not indexed to the Company’s own stock are classified as a liability on the Company’s balance sheet. The common stock warrants are recorded at fair value, estimated using the Black-Scholes option-pricing model, and marked to market at each balance sheet date with changes in the fair value of the liability recorded in other income (expense), net in the statements of operations.
Revenue recognition	Effective January 1, 2018, the Company adopted the provisions of Accounting Standards Codification (“ASC”) 606, Revenue from Contracts with Customers using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance, while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605). Under ASC 605, the Company’s revenue recognition accounting policy was consistent with ASC 606 revenue recognition accounting policies, except the Company used to recognize upfront license fees on a straight line basis. Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that are within the scope of ASC 606, the Company performs the following five steps: 1. Identify the contract with the customer. A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance, and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. The Company applies judgment in determining the customer’s intent and ability to pay, which is based on a variety of factors including the customer’s historical payment experience, or in the case of a new customer, published credit and financial information pertaining to the customer. 2. Identify the performance obligations in the contract. Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are both capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. 3. Determine the transaction price. The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method, depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment. 4. Allocate the transaction price to performance obligations in the contract. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. However, if a series of distinct services that are substantially the same qualifies as a single performance obligation in a contract with variable consideration, the Company must determine if the variable consideration is attributable to the entire contract or to a specific part of the contract. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. 5. Recognize revenue when or as the Company satisfies a performance obligation. The Company satisfies performance obligations either over time or at a point in time. Revenue is recognized over time if either (i) the customer simultaneously receives and consumes the benefits provided by the entity’s performance, (ii) the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or (iii) the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. Examples of control are using the asset to produce goods or services, enhance the value of other assets, or settle liabilities, and holding or selling the asset. Licenses of intellectual property : If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from consideration allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the licenses. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: At the inception of each arrangement that includes development milestone payments, the Company evaluates the probability of reaching the milestones and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur in the future, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received and therefore revenue recognized is constrained as management is unable to assert that a reversal of revenue would not be possible. The transaction price is then allocated to each performance obligation on a relative standalone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues and earnings in the period of adjustment. Royalties : For arrangements that include sales-based royalties, including milestone payments based on levels of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaboration agreements.
Equity-based compensation	Equity-based compensation The Company measures the cost of common stock option awards at fair value and records the cost of the awards, net of estimated forfeitures, on a straight-line basis over the requisite service period. The Company measures fair value for all common stock options using the Black-Scholes option-pricing model. For all common stock option awards to employees, the fair value measurement date is the date of grant and the requisite service period is the period over which the employee is required to provide service in exchange for the common stock option awards, which is generally the vesting period. For all common stock option awards to nonemployees, the Company remeasures fair value at each financial statement reporting date and recognizes compensation expense as services are rendered, generally on a straight-line basis.
Segments and geographic information	Segments and geographic information The Company has determined it has one reporting segment. Disaggregating the Company’s operations is impracticable because the Company’s research and development activities and its assets overlap and management reviews its business as a single operating segment. Thus, discrete financial information is not available by more than one operating segment. All long-lived assets of the Company are located in the United States.
Deferred rent	Deferred rent Deferred rent consists of rent escalation payment terms, tenant improvement allowances and other incentives received from the landlord related to the Company’s operating lease and is presented in “Other noncurrent assets” in the accompanying balance sheet. Rent escalation represents the difference between actual operating lease payments due and straight-line rent expense, which is recorded by the Company over the term of the lease. Tenant improvement allowances and other incentives are recorded as deferred rent and amortized as a reduction of periodic rent expense, over the term of the applicable lease.
Research and development expense	Research and development expense Research and development expense includes wages, benefits, research materials, external services, legal fees related to patent protection, overhead and other expenses directly related to research and development operations. Research and development costs are expensed as incurred in accordance with ASC 730, Research and Development. Research and development costs that are paid in advance of performance are deferred as a prepaid expense and recognized as expense as the services are provided.
Income taxes	Income taxes From inception through July 9, 2015, the Company was a Delaware LLC for federal and state tax purposes and, therefore, all items of income or loss through July 9, 2015 flowed through to the members of AuraSense Therapeutics, LLC. Effective July 9, 2015, the Company converted from an LLC to a C corporation for federal and state income tax purposes. Accordingly, prior to the conversion to a C corporation, the Company did not record deferred tax assets or liabilities or have any net operating loss carryforwards. The Company recognizes deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of its assets and liabilities and the expected benefits of net operating loss carryforwards. The impact of changes in tax rates and laws on deferred taxes, if any, is applied during the years in which temporary differences are expected to be settled and is reflected in the financial statements in the period of enactment. The measurement of deferred tax assets is reduced, if necessary, if, based on weight of the evidence, it is more likely than not that some, or all, of the deferred tax assets will not be realized. At December 31, 2018 and 2017, the Company established a full valuation allowance against its deferred tax assets to an amount that is more likely than not to be realized.
Recent accounting pronouncements	Recently Adopted Accounting Pronouncements Revenue Recognition In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09 (ASC 606), Revenue from Contracts with Customers . This ASU, as amended by ASU 2015-14, affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. ASU 2014-09 replaces most existing revenue recognition guidance in GAAP when it becomes effective. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the currently effective guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is effective for Exicure in the first quarter of 2018 and early adoption is permitted beginning in the first quarter of 2017. The Company adopted ASC 606 on a modified retrospective basis. See above “Revenue Recognition” for a discussion of the Company’s updated policies related to revenue recognition effective January 1, 2018. Impact of adoption of ASC 606 The Company adopted ASC 606 using the modified retrospective method. The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new guidance, the Company recorded reductions to both accumulated deficit and deferred revenue, current of $1,034 as of the date of adoption. As a result of the adoption of ASC 606: (i) there were no impacts to the totals of our cash flows from operating activities, cash flows from investing activities, or cash flows from financing activities in the accompanying consolidated statement of cash flows for the year ended December 31, 2018; (ii) there were no impacts to the balances of the accompanying consolidated balance sheet as of December 31, 2018, and (iii) total revenue, operating loss, and net loss were lower by $1,034 each in the accompanying consolidated statement of operations for the year ended December 31, 2018. Cash Flows In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . ASU 2016-15 addresses the classification of certain specific cash flow issues including debt prepayment or extinguishment costs, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of certain insurance claims and distributions received from equity method investees. ASU 2016-15 is effective for the Company in the first quarter of 2018 and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company adopted this guidance on January 1, 2018. The adoption of ASU 2016-15 did not have a material impact to the Company’s statement of cash flows. Stock-Based Compensation In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting . ASU 2017-09 clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. ASU 2017-09 will be applied prospectively to awards modified on or after the adoption date. ASU 2017-09 is effective for the Company for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted. The Company adopted this guidance on January 1, 2018. The adoption of ASU 2017-09 did not have a material impact to the Company’s financial statements. Recent Accounting Pronouncements Not Yet Adopted Leases In February 2016, FASB issued ASU 2016-02, Leases (Topic 842) , which requires lessees to recognize right-of-use assets and lease liabilities on the balance sheet. ASU 2016-02 is to be applied using a modified retrospective approach at the beginning of the earliest comparative period in the financial statements. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. ASU 2016-02 requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”), which allows entities to initially apply the new lease guidance at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We expect to adopt the new standard on January 1, 2019 and use the effective date as our date of initial application. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The Company is in the process of gathering a complete inventory of its lease contracts and evaluating the impact of the new guidance on its consolidated financial statements and related disclosures; however, management expects that the adoption of ASU 2016-02 will result in the recognition of a right-of-use asset and related liability associated with the Company’s non-cancelable operating lease arrangement for office and laboratory space that was executed in 2012 (see Note 12, Commitments and Contingencies ).
Loss per common share	Basic loss per common share is calculated by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted loss per common share is calculated using the treasury share method by giving effect to all potentially dilutive securities that were outstanding. Potentially dilutive options and warrants to purchase common stock that were outstanding during the periods presented were excluded from the diluted loss per share calculation because such shares had an anti-dilutive effect due to the net loss reported in those periods.
Fair Value Measurements	Fair Value Measurements ASC Topic 820, Fair Value Measurement, establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, as follows: Level 1 Inputs - unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date; Level 2 Inputs - other than quoted prices included in Level 1 inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability; and Level 3 Inputs - unobservable inputs for the asset or liability used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at measurement date. The Company uses the market approach and Level 1 inputs to value its cash equivalents. The Company’s long-term debt bore interest at the prevailing market rates for instruments with similar characteristics and, accordingly, the carrying value for this instrument also approximates its fair value and the financial measurement is also classified within Level 2 of the fair value hierarchy. The Company’s common stock warrant liability (refer to Note 6, Stockholders’ Equity , for more information) and preferred stock warrant liability (terminated on September 26, 2017 in connection with the Merger; see Note 5, Debt , for more information) are classified within Level 3 of the fair value hierarchy. The fair values of the common stock warrant liability and preferred stock warrant liability were determined using the Black-Scholes option-pricing model.

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Balance Sheet Information [Abstract]
Property, Plant and Equipment	Property and equipment, net December 31, 2018 2017 Scientific equipment $ 1,979 $ 1,797 Leasehold improvements 192 192 Furniture and fixtures 41 31 Computers and software 26 26 Construction in process 12 120 Property and equipment, gross 2,250 2,166 Less: accumulated depreciation (1,189 ) (849 ) Property and equipment, net $ 1,061 $ 1,317
Schedule of Accrued Liabilities	Accrued expenses and other current liabilities December 31, 2018 2017 Accrued legal expenses $ 189 $ 251 Accrued payroll-related expenses 899 718 Accrued clinical, contract research and manufacturing costs 102 205 Other accrued expenses 353 99 Accrued expenses and other current liabilities $ 1,543 $ 1,273

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Principal Maturities of Long-term Debt	At December 31, 2018, the principal maturities of the long-term debt were as follows: December 31, 2018 2019 $ — 2020 4,999 Principal balance outstanding 4,999 less: unamortized discount (69 ) less: unamortized debt issuance costs (5 ) Long-term debt 4,925 Current portion — Noncurrent portion $ 4,925

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-Based Compensation Expense Classification in Statement of Operations	Equity-based compensation expense is classified in the statements of operations as follows: Year Ended December 31, 2018 2017 Research and development expense $ 485 $ 172 General and administrative expense 1,324 1,290 $ 1,809 $ 1,462
Assumptions Used to Determine Fair Value of Common Stock Option Grants	The fair value of the underlying common stock and the exercise price for the common stock options granted during the years ended December 31, 2018 and 2017 are summarized in the table below: Common Stock Options Granted During Period Ended: Fair Value of Underlying Common Stock Exercise Price of Common Stock Option Year ended December 31, 2018 $3.00 to $5.82; weighted avg. $3.45 $3.00 to $5.82; weighted avg. $3.45 Year ended December 31, 2017 $4.21 $4.21 In addition to an assumption on the expected term of the option grants as discussed below, application of the Black-Scholes model requires additional inputs for which we have assumed the values described in the table below: Year Ended December 31, 2018 2017 Expected term 5.3 to 6.0 years 5.3 to 6.5 years Risk-free interest rate 2.72% to 2.87%; weighted avg. 2.78% 1.97% to 2.17%; weighted avg. 2.07% Expected volatility 78.1% to 82.4%; weighted avg. 80.6% 80.8% to 83.1%; weighted avg. 81.0% Forfeiture rate 5 % 5 % Expected dividend yield — % — %
Common Stock Option Activity	A summary of common stock option activity as of the periods indicated is as follows: Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value (thousands) Outstanding - December 31, 2017 3,672,620 $ 1.79 7.5 $ 5,221 Granted 1,277,744 3.45 Exercised (22,494 ) 1.81 Forfeited (36,282 ) 2.29 Outstanding - December 31, 2018 4,891,588 $ 2.22 7.3 $ 7,330 Exercisable - December 31, 2018 3,238,798 $ 1.70 6.7 $ 6,352 Vested and Expected to Vest - December 31, 2018 4,799,984 $ 2.20 7.3 $ 7,287

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	The differences between income taxes computed using the U.S. federal income tax rate and the provision for income taxes are as follows: Year Ended December 31, 2018 2017 Federal income tax expense at statutory rate $ (4,707 ) 21.0 % $ (4,093 ) 34.0 % State income tax expense at statutory rate (1,595 ) 7.1 (610 ) 5.1 Permanent differences 243 (1.1 ) (125 ) 1.0 Impact of Tax Reform Act — — 3,760 (31.2 ) Other — — (10 ) 0.1 Change in valuation allowance 6,059 (27.0 ) 1,078 (9.0 ) $ — — % $ — — %
Schedule of Deferred Tax Assets and Liabilities	The significant components of the Company’s net deferred tax assets are as follows: December 31, 2018 2017 Deferred Tax Assets Net operating losses $ 14,827 $ 8,748 Intangibles 187 205 Accrued expenses 271 198 Equity-based compensation 796 728 Deferred revenue — 295 Other 204 — Less: Valuation allowance (16,225 ) (10,166 ) Total deferred tax assets 60 8 Deferred Tax Liabilities Fixed assets and other (60 ) (8 ) Total deferred tax liabilities (60 ) (8 ) Deferred taxes, net $ — $ —

Loss Per Common Share (Tables)

Loss Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Computation of Loss Per Common Share	The following is the computation of loss per common share for the years ended December 31, 2018 and 2017: Year Ended December 31, 2018 2017 Net loss $ (22,413 ) $ (11,011 ) Weighted-average basic and diluted common shares outstanding 41,189,177 10,119,569 Loss per share - basic and diluted $ (0.54 ) $ (1.09 )
Antidilutive Securities	The outstanding securities presented below were excluded from the calculation of net loss per common share, because such securities would have been anti-dilutive due to the Company’s net loss per share during the periods ending on the dates presented: December 31, 2018 2017 Options to purchase common stock 4,891,588 3,672,620 Warrants to purchase common stock 413,320 413,320

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Assumptions used to Estimate Fair Value of Warrant Liability	The following weighted-average assumptions were used to estimate the fair value of the common stock warrant liability at December 31, 2018: December 31, 2018 Expected term 2.3 Risk-free interest rate 2.46 % Expected volatility 86.74 % Expected dividend yield — %
Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis	The following is a reconciliation of the Company’s liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3) for the years ended December 31, 2018 and 2017: Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Preferred Stock Warrant Liability Common Stock Warrant Liability Total Balance at January 1, 2017 $ 201 $ — $ 201 Additions — 536 536 Gain included in other income (expense), net (201 ) (13 ) (214 ) Balance at December 31, 2017 $ — $ 523 $ 523 Loss included in other income (expense), net — 274 274 Balance at December 31, 2018 $ — $ 797 $ 797

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Rent Expense	Rent expense consisted of the following: Years Ended December 31, 2018 2017 Straight-line rent expense $ 332 $ 332 Contingent rent expense 298 281 Total rent expense $ 630 $ 613
Schedule of Future Minimum Rental Payments	Future minimum lease payments as of December 31, 2018 are as follows: Years Ending December 31, Operating Leases 2019 347 2020 353 2021 59 Thereafter — Total $ 759

Related-Party Transactions (Tab

Related-Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Schedule of Revenue from Related Party	The following is a summary of amounts billed to AuraSense, LLC and recognized in the accompanying consolidated statement of operations in connection with the above mentioned activities: For the Years Ended December 31, 2018 2017 Quarterly fee for indirect costs $ 12 $ 12 Direct costs of AuraSense LLC paid by the Company 26 5 $ 38 $ 17

Quarterly Financial Data (Una_2

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	Selected quarterly financial data for the years ended December 31, 2018 and 2017 are as follows: 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Revenue (1) 36 19 57 6 Net loss (1)(2) (5,509 ) (6,825 ) (5,324 ) (4,755 ) Basic and diluted loss per common share (3) $ (0.14 ) $ (0.17 ) $ (0.13 ) $ (0.11 ) 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Revenue 2,432 2,695 2,497 2,095 Net loss (2,652 ) (2,984 ) (1,932 ) (3,443 ) Basic and diluted loss per common share (3) $ (15.62 ) $ (15.70 ) $ (1.12 ) $ (0.09 ) ___________ (1) - As discussed in Note 2, Significant Accounting Policies - Recently Adopted Accounting Pronouncements , the Company adopted ASC 606 on a modified retrospective basis effective January 1, 2018. As a result of the adoption of ASC 606, total revenue and net loss were lower by $1,034 each in the three months ended March 31, 2018. (2) - Net loss includes a non-cash unrealized (loss) gain related to the fair value adjustment of the common stock warrant liability of ($128) , ($915) , $581 , and $186 in the three months ended March 31, 2018, June 30, 2018, September 30, 2018, and December 31, 2018, respectively. (3) - As discussed in Note 1, Description of Business and Basis of Presentation - The Merger , shares of preferred stock issued and outstanding immediately prior to the closing of the Merger were converted into an aggregate of 26,476,543 shares of common stock. As such, these shares of common stock are included in the computation of basic and diluted loss per common share beginning with September 26, 2017 and excluded from the computation of basic and diluted loss per common share for dates prior to September 26, 2017.

Description of Business and B_2

Description of Business and Basis of Presentation - Description of Business (Details) $ in Thousands	Sep. 26, 2017shares	Jul. 09, 2015USD ($)	Dec. 12, 2011USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares
Conversion of Stock [Line Items]
Common stock, shares outstanding (in shares) | shares				44,358,000	39,300,823
Property and equipment, gross | $				$ 2,250	$ 2,166
Accumulated deficit generated, since inception | $				(73,831)
Common Stock
Conversion of Stock [Line Items]
Conversion ratio		1
Shares issued in conversion of stock (in shares) | shares	26,476,543
Exicure OpCo Common and Preferred, Excluding Series C Preferred
Conversion of Stock [Line Items]
Percent ownership after transaction	94.00%
Class A Units
Conversion of Stock [Line Items]
Issuance of stock, net (in shares) | shares			11,381,611
Subsidiary of Common Parent
Conversion of Stock [Line Items]
Unbilled revenue receivable | $			$ 143
Accrued legal expenses | $			317
Capital contribution at net book value | $			135
Reclassification to additional paid in capital | $		$ 18,837
Scientific equipment
Conversion of Stock [Line Items]
Property and equipment, gross | $				$ 1,979	$ 1,797
Scientific equipment | Subsidiary of Common Parent
Conversion of Stock [Line Items]
Property and equipment, gross | $			$ 309
Exicure OpCo 2015 Equity Incentive Plan
Conversion of Stock [Line Items]
Number of options converted (in shares) | shares	7,414,115
Exicure, Inc. 2017 Equity Incentive Plan
Conversion of Stock [Line Items]
Conversion grants in the period (in shares) | shares	3,680,997
Common and Preferred Stock, Excluding Series C Preferred Stock Converted into Max-1 Common Stock
Conversion of Stock [Line Items]
Conversion ratio	0.49649
Series C Preferred Stock Converted into Max-1 Common Stock
Conversion of Stock [Line Items]
Conversion ratio	0.7666652
Conversion of Common Unit of AuraSense Therapeutics, LLC Into One Share of Common Stock of Exicure OpCo
Conversion of Stock [Line Items]
Conversion ratio		1
Conversion of Class A Unit of AuraSense Therapeutics, LLC Into One Share of Series A Preferred Stock of Exicure OpCo
Conversion of Stock [Line Items]
Conversion ratio		1
Conversion of Class B-1 Unit of AuraSense Therapeutics, LLC Into One Share of Series B-1 Preferred Stock of Exicure OpCo
Conversion of Stock [Line Items]
Conversion ratio		1
Conversion of Class B-2 Unit of AuraSense Therapeutics, LLC Into One Share of Series B-2 Preferred Stock of Exicure OpCo
Conversion of Stock [Line Items]
Conversion ratio		1
Conversion of Class C Unit of AuraSense Therapeutics, LLC Into One Share of Series C Preferred Stock of Exicure OpCo
Conversion of Stock [Line Items]
Conversion ratio		1
Conversion of Options to Purchase Common Units of AuraSense Therapeutics, LLC Into Options to Purchase Common Stock of Exicure OpCo
Conversion of Stock [Line Items]
Option conversion ratio		1
Northwestern University | Class A Units
Conversion of Stock [Line Items]
Percent of units received			1.00%
Number of units received (in shares) | shares			113,816
Pre-Merger Shareholders | Investor
Conversion of Stock [Line Items]
Common stock, shares outstanding (in shares) | shares	2,080,000
Pre-Merger Shareholders | Investor | Common Stock
Conversion of Stock [Line Items]
Shares issued in conversion of stock (in shares) | shares	26,666,627

Description of Business and B_3

Description of Business and Basis of Presentation - Schedule of Error Corrections (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments
Prepaid expenses and other assets	$ 1,382				$ 1,844				$ 1,382	$ 1,844
Accrued expenses	1,543				1,273				1,543	1,273
Accumulated deficit	(54,994)				(33,615)				(54,994)	(33,615)
Research and development expense									14,119	13,080
Operating loss									21,819	10,407
Net loss	$ (4,755)	$ (5,324)	$ (6,825)	$ (5,509)	$ (3,443)	$ (1,932)	$ (2,984)	$ (2,652)	$ (22,413)	$ (11,011)
Loss per share - basic and diluted (in dollars per share)	$ 0.11	$ 0.13	$ 0.17	$ 0.14	$ 0.09	$ 1.12	$ 15.70	$ 15.62	$ 0.54	$ 1.09
Immaterial Error Corrections
Error Corrections and Prior Period Adjustments
Prepaid expenses and other assets					$ 933					$ 933
Accrued expenses					(95)					(95)
Accumulated deficit					$ 1,028					1,028
Research and development expense										(1,369)
Operating loss										1,369
Net loss										$ 1,028
Loss per share - basic and diluted (in dollars per share)										$ 0.10

Significant Accounting Polici_3

Significant Accounting Policies - Concentrations of Credit Risk and Other Risks and Uncertainties (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 26,268	$ 25,764	$ 19,623

Significant Accounting Polici_4

Significant Accounting Policies - Property and Equipment (Details) - USD ($)	12 Months Ended	85 Months Ended
	Dec. 31, 2018	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Impairment losses		$ 0
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years

Significant Accounting Polici_5

Significant Accounting Policies - Segments and Geographic Information (Details)	12 Months Ended
	Dec. 31, 2018segment
Accounting Policies [Abstract]
Number of reporting segments	1
Number of operating segments	1

Significant Accounting Polici_6

Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents	$ 26,268				$ 25,764				$ 26,268	$ 25,764	$ 19,623
Adoption of new accounting standard - ASC 606					1,034					1,034
Accumulated deficit	(54,994)				(33,615)				(54,994)	(33,615)
Deferred revenue, current	0				1,034				0	1,034
Revenues	6	$ 57	$ 19	$ 36	2,095	$ 2,497	$ 2,695	$ 2,432	118	9,719
Operating loss									(21,819)	(10,407)
Net loss	$ (4,755)	$ (5,324)	$ (6,825)	(5,509)	(3,443)	$ (1,932)	$ (2,984)	$ (2,652)	(22,413)	(11,011)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current					1,034					1,034
Revenues				1,034					(1,034)
Operating loss									1,034
Net loss				$ 1,034					1,034
Accumulated Deficit
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Adoption of new accounting standard - ASC 606					$ 1,034					1,034
Net loss									$ (22,413)	$ (11,011)
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated useful lives									3 years
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated useful lives									7 years

Purdue Collaboration (Details)

Purdue Collaboration (Details) $ in Thousands	Dec. 02, 2016USD ($)target	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current portion of deferred revenue		$ 0	$ 1,034
Purdue Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current portion of deferred revenue			1,034
Collaboration revenue		$ 118	9,719
Reimbursable research and development activities			$ 1,443
Purdue Collaboration | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of additional collaboration targets | target	3
Non-refundable upfront payment received for research agreement	$ 10,000
Potential milestone revenue	776,500
Aggregate research milestone revenue	16,500
Aggregate regulatory milestone revenue	410,000
Aggregate commercial milestone revenue	$ 350,000
Purdue Collaboration | Maximum | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Commercial sales royalty, percent	10.00%

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,250	$ 2,166
Less: accumulated depreciation	(1,189)	(849)
Property and equipment, net	1,061	1,317
Depreciation and amortization	358	232
Scientific equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,979	1,797
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	192	192
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	41	31
Computers and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	26	26
Construction in process
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 12	$ 120

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Accrued Expense and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Supplemental Balance Sheet Information [Abstract]
Accrued legal expenses	$ 189	$ 251
Accrued payroll-related expenses	899	718
Accrued clinical, contract research and manufacturing costs	102	205
Other accrued expenses	353	99
Accrued expenses and other current liabilities	$ 1,543	$ 1,273

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($)	Jan. 15, 2018	Feb. 17, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2020
Debt Instrument [Line Items]
Unamortized debt issuance costs			$ 5,000
Unamortized discount			69,000
Long-term debt			4,925,000	$ 4,855,000
Interest paid			$ 572,000	$ 611,000
Hercules Technology Growth Capital | Secured Debt | Loans Payable
Debt Instrument [Line Items]
Loan facility		$ 10,000,000
Initial draw amount		6,000,000
Proceeds net of issuance costs		$ 5,839,000
Debt payments deferred, consecutive period	13 months
Hercules Technology Growth Capital | Secured Debt | Loans Payable | Prime Rate
Debt Instrument [Line Items]
Floating interest rate (as a percent)		9.95%
Reduction of prime rate (as a percent)		3.50%
Series C | Hercules Technology Growth Capital | Secured Debt | Loans Payable
Debt Instrument [Line Items]
Shares issuable on debt instrument (in shares)		80,000
Exercise price (in dollars per share)		$ 3
Preferred stock warrant liability		$ 134,000
Unamortized discount		$ 134,000
Minimum | Hercules Technology Growth Capital | Secured Debt | Loans Payable
Debt Instrument [Line Items]
Interest rate, stated percentage		9.95%
Fees at Issuance | Hercules Technology Growth Capital | Secured Debt | Loans Payable
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ 161,000
Fees at Maturity | Hercules Technology Growth Capital | Secured Debt | Loans Payable
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ 231,000
Scenario, Forecast | Hercules Technology Growth Capital | Secured Debt | Loans Payable
Debt Instrument [Line Items]
Amortization of principal and interest, consecutive period					18 months

Debt - Principal Maturities of

Debt - Principal Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
2,019	$ 0
2,020	4,999
Principal balance outstanding	4,999
less: unamortized discount	(69)
less: unamortized debt issuance costs	(5)
Long-term debt	4,925	$ 4,855
Current portion	0
Noncurrent portion	$ 4,925	$ 4,855

Stockholders' Equity - Current

Stockholders' Equity - Current Capitalization (Details)	Dec. 31, 2018vote_per_share$ / sharesshares	Dec. 31, 2017$ / sharesshares
Equity [Abstract]
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.0001	$ 0.0001
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.0001	$ 0.0001
Common stock, shares issued (in shares)	44,358,000	39,300,823
Common stock, shares outstanding (in shares)	44,358,000	39,300,823
Common stock, voting rights for each share | vote_per_share	1

Stockholders' Equity - Private

Stockholders' Equity - Private Placement Post-Merger and Registration Rights (Details) $ / shares in Units, $ in Thousands	Aug. 22, 2018USD ($)$ / sharesshares	Feb. 01, 2018shares	Nov. 02, 2017USD ($)shares	Sep. 26, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)investor$ / sharesshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)$ / sharesshares	Oct. 05, 2018shares	Feb. 06, 2018shares	Oct. 26, 2017$ / shares
Class of Stock [Line Items]
Proceeds from common stock offering | $						$ 22,001	$ 31,513
Issuance of common stock to consultants, net (in shares)		145,466
Private Placement
Class of Stock [Line Items]
Shares issued in sale of stock (in shares)	4,889,217		3,736,836	6,767,360	10,504,196
Price per share in sale of stock (in dollars per share) | $ / shares	$ 4.50			$ 3						$ 0.0001
Proceeds from common stock offering | $	$ 22,001
Stock issuance costs | $	1,931			$ 3,037	$ 3,966
Proceeds received from sale of stock, gross | $	$ 20,070		$ 11,211	$ 17,235	$ 31,513
Issuance of stock, net (in shares)	4,889,217				50,000
Payments to private placement agents for private placement | $	$ 1,680				$ 1,968
Expenses reimbursed to placement agents | $	$ 87
Shares available for sale of stock (in shares)				13,333,333
Number of shares called by warrants (in shares)					413,320	413,320	413,320
Exercise price (in dollars per share) | $ / shares					$ 3		$ 3
Anti-dilution protection period					18 months
Number of investors with largest number of held shares | investor					3
Common Stock
Class of Stock [Line Items]
Shares registered for resale (in shares)									39,714,143
Common Stock
Class of Stock [Line Items]
Shares registered for resale (in shares)								5,034,683

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock Warrants (Details) - Private Placement - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Number of shares called by warrants (in shares)	413,320	413,320
Exercise price (in dollars per share)		$ 3

Stockholders' Equity - The Merg

Stockholders' Equity - The Merger and Other - Prior to the Merger (Details) $ / shares in Units, $ in Thousands	Sep. 26, 2017shares	Jan. 11, 2016USD ($)$ / sharesshares	Jul. 09, 2015	Dec. 31, 2017shares	Dec. 31, 2018shares
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)				39,300,823	44,358,000
Liquidation preference, percent of aggregate cash contributions				1.5
Common Stock
Class of Stock [Line Items]
Conversion ratio			1
Shares issued in conversion of stock (in shares)	26,476,543
Series C Preferred Stock
Class of Stock [Line Items]
Shares issued in sale of stock (in shares)		149,999
Price per share in sale of stock (in dollars per share) | $ / shares		$ 3
Proceeds received from sale of stock, gross | $		$ 450
Stock issuance costs | $		6
Proceeds from preferred stock offering | $		$ 444
Common and Preferred Stock, Excluding Series C Preferred Stock Converted into Max-1 Common Stock
Class of Stock [Line Items]
Conversion ratio	0.49649
Series C Preferred Stock Converted into Common Stock
Class of Stock [Line Items]
Conversion ratio	0.7666652
Pre-Merger Shareholders | Investor
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)	2,080,000
Pre-Merger Shareholders | Investor | Common Stock
Class of Stock [Line Items]
Shares issued in conversion of stock (in shares)	26,666,627
Exicure OpCo 2015 Equity Incentive Plan
Class of Stock [Line Items]
Number of options converted (in shares)	7,414,115
Exicure, Inc. 2017 Equity Incentive Plan
Class of Stock [Line Items]
Conversion grants in the period (in shares)	3,680,997

Equity-Based Compensation - Nar

Equity-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 22, 2017	Oct. 06, 2015	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized			$ 3,172
Compensation expense recognition period			2 years 6 months
Weighted-average grant date fair value (in dollars per share)			$ 2.40	$ 2.92
Intrinsic value of options exercised			$ 44	$ 202
Exicure, Inc. 2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	5,842,525
Number of shares available for grant (in shares)	2,169,905		928,443
Potential maximum additional shares (in shares)	4,600,000
Percentage of common stock outstanding	5.00%
Exicure OpCo 2015 Equity Incentive Plan | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	3,683,817
Expiration period		10 years
Exicure OpCo 2015 Equity Incentive Plan | Initial Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		48 months
Exicure OpCo 2015 Equity Incentive Plan | Subsequent Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		48 months
Share-based Compensation Award, Tranche One | Exicure OpCo 2015 Equity Incentive Plan | Initial Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Share-based Compensation Award, Tranche Two | Initial Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		2.08%
Share-based Compensation Award, Tranche Two | Subsequent Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		2.08%

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 1,809	$ 1,462
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	485	172
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 1,324	$ 1,290

Equity-Based Compensation - Ass

Equity-Based Compensation - Assumptions Used for Fair Value Measurement (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture rate	5.00%	5.00%
Expected dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years 3 months 18 days	5 years 3 months 18 days
Risk-free interest rate	2.72%	1.97%
Expected volatility rate	78.10%	80.80%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 years	6 years 6 months
Risk-free interest rate	2.87%	2.17%
Expected volatility rate	82.40%	83.10%
Weighted Average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.78%	2.07%
Expected volatility rate	80.60%	81.00%

Equity-Based Compensation - Fai

Equity-Based Compensation - Fair Value of Underlying Common Stock and Exercise Price of Stock Options (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value of Underlying Common Stock (dollars per share)		$ 4.21
Exercise Price of Common Stock Option (dollars per share)		$ 4.21
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value of Underlying Common Stock (dollars per share)	$ 3
Exercise Price of Common Stock Option (dollars per share)	3
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value of Underlying Common Stock (dollars per share)	5.82
Exercise Price of Common Stock Option (dollars per share)	5.82
Weighted Average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value of Underlying Common Stock (dollars per share)	3.45
Exercise Price of Common Stock Option (dollars per share)	$ 3.45

Equity-Based Compensation - S_2

Equity-Based Compensation - Schedule of Stock Options Rollforward (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Options
Shares outstanding, beginning period	3,672,620
Granted, shares	1,277,744
Exercised, shares	(22,494)
Forfeited, shares	(36,282)
Shares outstanding, ending period	4,891,588	3,672,620
Weighted-Average Exercise Price
Weighted-Average Exercise Price, beginning period (dollars per share)	$ 1.79
Weighted-Average Exercise Price, granted (dollars per share)	3.45
Weighted-Average Exercise Price, exercised (dollars per share)	1.81
Weighted-Average Exercise Price, forfeitures (dollars per share)	2.29
Weighted-Average Exercise Price, ending period (dollars per share)	$ 2.22	$ 1.79
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-Average Remaining Contractual Term (years)	7 years 3 months	7 years 6 months
Aggregate Intrinsic Value (thousands)	$ 7,330	$ 5,221
Exercisable, shares	3,238,798
Exercisable, Weighted-Average Exercise Price (dollars per share)	$ 1.70
Exercisable, Weighted-Average Remaining Contractual Term	6 years 8 months
Exercisable, Aggregate Intrinsic Value	$ 6,352
Vested and Expected to Vest, shares	4,799,984
Vested and Expected to Vest, Weighted-Average Exercise Price (dollars per share)	$ 2.20
Vested and Expected to Vest, Weighted-Average Remaining Contractual Term (years)	7 years 3 months
Vested and Expected to Vest, Aggregate Intrinsic Value (dollars per share)	$ 7,287

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Net loss	$ (4,755,000)	$ (5,324,000)	$ (6,825,000)	$ (5,509,000)	$ (3,443,000)	$ (1,932,000)	$ (2,984,000)	$ (2,652,000)	$ (22,413,000)	$ (11,011,000)
Provision for income tax expense									$ 0	$ 0
Effective tax rate									0.00%	0.00%
Impact of Tax Reform Act										$ 3,760,000
Unrecognized tax benefits	0				$ 0				$ 0	$ 0
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	52,629,000								52,629,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	$ 50,294,000								$ 50,294,000

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal income tax expense at statutory rate	$ (4,707,000)	$ (4,093,000)
State income tax expense at statutory rate	(1,595,000)	(610,000)
Permanent differences	243,000	(125,000)
Impact of Tax Reform Act	0	3,760,000
Other	0	(10,000)
Change in valuation allowance	6,059,000	1,078,000
Provision for income tax expense	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal income tax expense at statutory rate	21.00%	34.00%
State income tax expense at statutory rate	7.10%	5.10%
Permanent differences	(1.10%)	1.00%
Impact of Tax Reform Act	0.00%	(31.20%)
Other	0.00%	0.10%
Change in valuation allowance	(27.00%)	(9.00%)
Effective tax rate	0.00%	0.00%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets
Net operating losses	$ 14,827	$ 8,748
Intangibles	187	205
Accrued expenses	271	198
Equity-based compensation	796	728
Deferred revenue	0	295
Other	204	0
Less: Valuation allowance	(16,225)	(10,166)
Total deferred tax assets	60	8
Deferred Tax Liabilities
Fixed assets and other	(60)	(8)
Total deferred tax liabilities	(60)	(8)
Deferred taxes, net	$ 0	$ 0

Loss Per Common Share - Computa

Loss Per Common Share - Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (4,755)	$ (5,324)	$ (6,825)	$ (5,509)	$ (3,443)	$ (1,932)	$ (2,984)	$ (2,652)	$ (22,413)	$ (11,011)
Weighted-average basic and diluted common shares outstanding (in shares)									41,189,177	10,119,569
Loss per share - basic and diluted (in dollars per share)	$ (0.11)	$ (0.13)	$ (0.17)	$ (0.14)	$ (0.09)	$ (1.12)	$ (15.70)	$ (15.62)	$ (0.54)	$ (1.09)

Loss Per Common Share - Antidil

Loss Per Common Share - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares excluded from computation of weighted-average diluted common shares outstanding (in shares)	4,891,588	3,672,620
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares excluded from computation of weighted-average diluted common shares outstanding (in shares)	413,320	413,320

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 26, 2017	Dec. 31, 2016USD ($)	Feb. 17, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impact of 10% change in expected volatility rate	$ 53
Impact of 10% change in the estimate of fair value of the common stock	$ 118
Risk-free interest rate | Warrant Liability | Non-Redeemable Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input					0.0153
Risk-free interest rate | Warrant Liability | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input	0.0246		0.0126
Expected term | Warrant Liability | Non-Redeemable Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input, term					2 years
Expected term | Warrant Liability | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input, term	2 years 3 months		5 years
Expected volatility | Warrant Liability | Non-Redeemable Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input					0.7897
Expected volatility | Warrant Liability | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input	0.8674		0.6299
Expected dividend yield | Warrant Liability | Non-Redeemable Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input					0
Expected dividend yield | Warrant Liability | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability, measurement input	0		0
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) | Warrant Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value liability	$ 797	$ 523		$ 201
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) | Warrant Liability | Non-Redeemable Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value liability	0	0		201
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) | Warrant Liability | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value liability	$ 797	$ 523		$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assumptions used to Estimate Fair Value of Warrant Liability (Details) - Warrant Liability - Common Stock	Dec. 31, 2018	Sep. 26, 2017
Expected term
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input, term	2 years 3 months	5 years
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	0.0246	0.0126
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	0.8674	0.6299
Expected dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	0	0

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value Measurements Using Significant Unobservable Inputs (Level 3) - Warrant Liability - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 523	$ 201
Additions		536
Gain (loss) included in other income (expense), net	(274)	214
Ending balance	797	523
Non-Redeemable Preferred Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	201
Additions		0
Gain (loss) included in other income (expense), net	0	201
Ending balance	0	0
Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	523	0
Additions		536
Gain (loss) included in other income (expense), net	(274)	13
Ending balance	$ 797	$ 523

Defined Contribution Plan - Nar

Defined Contribution Plan - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Retirement Benefits [Abstract]
Expense recognized on defined contribution savings plan	$ 107

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	76 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2014	Mar. 31, 2012
Commitments and Contingencies [Abstract]
Extended lease term				6 years
Deferred rent liability		$ 39	$ 48		$ 52
Aggregate consideration paid to NU for agreement obligations	$ 3,864

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Rent Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Straight-line rent expense	$ 332	$ 332
Contingent rent expense	298	281
Total rent expense	$ 630	$ 613

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Future Minimum Rental Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 347
2,020	353
2,021	59
Thereafter	0
Total	$ 759

Related-Party Transactions - Na

Related-Party Transactions - Narrative (Details) - USD ($) $ in Thousands	Jan. 01, 2017	Jan. 01, 2016	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Receivable from related party			$ 10	$ 17
Board of Directors | Consulting services
Related Party Transaction [Line Items]
Expenses from transactions with related party			$ 100
AuraSense
Related Party Transaction [Line Items]
Quarterly revenue from related party for indirect costs	$ 3	$ 8
Receivable from related party				$ 17

Related-Party Transactions - Sc

Related-Party Transactions - Schedule of Revenue from Related Party (Details) - AuraSense - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Revenue from related parties	$ 38	$ 17
Quarterly fee for indirect costs
Related Party Transaction [Line Items]
Revenue from related parties	12	12
Direct costs of AuraSense LLC paid by the Company
Related Party Transaction [Line Items]
Revenue from related parties	$ 26	$ 5

Quarterly Financial Data (Una_3

Quarterly Financial Data (Unaudited) - Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 26, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		$ 6	$ 57	$ 19	$ 36	$ 2,095	$ 2,497	$ 2,695	$ 2,432	$ 118	$ 9,719
Net loss		$ (4,755)	$ (5,324)	$ (6,825)	$ (5,509)	$ (3,443)	$ (1,932)	$ (2,984)	$ (2,652)	$ (22,413)	$ (11,011)
Basic and diluted loss per common share (in dollars per share)		$ (0.11)	$ (0.13)	$ (0.17)	$ (0.14)	$ (0.09)	$ (1.12)	$ (15.70)	$ (15.62)	$ (0.54)	$ (1.09)
Change in fair value of warrant liabilities		$ 186	$ 581	$ (915)	$ (128)					$ 274	$ (214)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue					1,034					(1,034)
Net loss					$ 1,034					$ 1,034
Common Stock
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Shares issued in conversion of stock (in shares)	26,476,543

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - Dermelix License Agreement - Collaborative Arrangement - Subsequent Event	Feb. 17, 2019USD ($)target
Subsequent Event [Line Items]
Number of additional collaboration targets | target	5
Term of license agreement	6 years
Non-refundable upfront payment received for research agreement	$ 1,000,000
Option exercise fee	$ 1,000,000
Period to exercise upon commencement of SNA technology development	30 days
Aggregate regulatory milestone revenue	$ 13,500,000
Potential milestone revenue	$ 152,500,000
Exercise termination period upon change of control	90 days