Summary of Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation and Consolidation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.
Basis of Consolidation	The consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Segment and geographic information	Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment.
Use of Estimates	Use of Estimates The preparation of financial statements and related disclosures in conformity with GAAP requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. The Company bases its estimates and judgments on historical experience and on various other assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company's Consolidated Balance Sheets and the amount of expenses reported for each of the periods presented are affected by estimates and assumptions, which are used for, but not limited to, accounting for research and development costs and accounting for share-based compensation. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents and Available-for-Sale Securities The Company considers all highly liquid investments with an original maturity of 90 days or less when purchased to be cash equivalents. The carrying amounts reported in the Company's Consolidated Balance Sheets for cash and cash equivalents are valued at cost, which approximates their fair value.
Available-for-Sale Securities	The Company considers debt securities with original maturities of greater than 90 days to be available-for-sale securities. Available-for-sale securities with original maturities of greater than one year are recorded as non-current assets. Available-for-sale securities are recorded at fair value and unrealized gains and losses are recorded within other comprehensive income. On a quarterly basis, the Company reviews the status of each security in an unrealized loss position, to evaluate the existence of potential credit losses. The Company first considers whether it intends to sell, or if it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through income. For securities that do not meet this criteria, the Company considers a number of factors to determine if the decline in fair value has resulted from credit losses or other factors, including but not limited to: (1) the extent of the decline; (2) changes to the rating of the security by a rating agency; (3) any adverse conditions specific to the security; and (4) other market conditions that may affect the fair value of the security. If this assessment indicates that a credit loss exists and the present value of cash flows expected to be collected is less than the amortized cost basis, an allowance for credit losses is required for the credit loss. Any impairment that has not been recorded through an allowance for credit losses is recognized in other comprehensive income.
Concentration of Credit Risk	Concentration of Credit Risk The Company's financial instruments that are exposed to concentration of credit risk consist primarily of cash, cash equivalents and available-for-sale securities. The Company maintains its cash in bank accounts, the balances of which generally exceed federally insured limits. The Company maintains its cash equivalents and available-for-sale securities in investments in money market funds, in U.S. Treasury securities, U.S. Government Agency securities, investment-grade corporate debt securities, asset-backed securities and debt instruments issued by foreign governments with original maturities of 90 days or less. The Company believes it is not exposed to significant credit risk on its cash, cash equivalents and available-for-sale securities.
Concentration of Suppliers	Concentration of Suppliers The Company historically relied upon a single third-party manufacturer to provide the drug substance for ACP on a purchase order basis. The Company also historically relied upon a single third-party manufacturer to provide fill/finish services for clinical supplies of ACP. The Company has engaged one additional third-party manufacturer to provide drug substance for ACP and one additional third-party manufacturer to provide fill/finish services for clinical supplies of ACP. In addition, the Company currently relies upon a single third-party supplier to supply on a purchase order basis the polyethylene glycol starting material used to manufacture ACP. Furthermore, the Company and its contract manufacturers currently rely upon sole-source suppliers of certain raw materials and other specialized components of production used in the manufacture and fill/finish of ACP. The Company currently relies upon a single third-party contract manufacturer to provide the drug substance for IC-500 for preclinical toxicology studies and early-stage clinical trials and a single third-party contract manufacturer to conduct fill/finish services for IC-500 drug product. If the Company’s third-party manufacturers or fill/finish service providers should become unavailable to the Company for any reason, including as a result of capacity constraints, different business objectives, financial difficulties, insolvency or the impact of COVID-19, the Company believes that there are a limited number of potential replacement manufacturers, and the Company likely would incur added costs and delays in identifying or qualifying such replacements.
Equity Investments	Equity Investments The Company holds investments in equity securities without a readily determinable fair value. Equity investments without a readily determinable fair value are recognized at fair value and are adjusted for observable price changes, or when qualitative assessments indicate that impairment exists, which is recorded in other income (loss).
Financial Instruments	Financial Instruments Cash equivalents are reflected in the accompanying financial statements at fair value. The carrying amount of accounts payable and accrued expenses, including accrued research and development expenses, approximates fair value due to the short-term nature of those instruments. The carrying amount of the Company's term loan approximates fair value due to the variable interest rate nature of the debt. Accounting Standards Codification, or ASC 820, Fair Value Measurements and Disclosures, defines fair value as the price that would be received to sell an asset, or paid to transfer a liability, in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. The fair value standard also establishes a three-level hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The Company reviews investments on a periodic basis for other than temporary impairments. This review is subjective as it requires management to evaluate whether an event or change in circumstances has occurred in the period that may have a significant adverse effect on the fair value of the investment. The Company uses the market approach to measure fair value for its cash, cash equivalents and available-for-sale financial assets. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability on the measurement date. The three levels are defined as follows: •Level 1—inputs to the valuation methodology are quoted prices (unadjusted) for an identical asset or liability in an active market. The Company's Level 1 assets consist of investments in money market funds and U.S. Treasury securities. •Level 2—inputs to the valuation methodology include quoted prices for a similar asset or liability in an active market or model-derived valuations in which all significant inputs are observable for substantially the full term of the asset or liability. The Company's Level 2 assets consist of investments in investment-grade corporate debt securities. •Level 3—inputs to the valuation methodology are unobservable and significant to the fair value measurement of the asset or liability. The Company does not hold any assets that are measured using Level 3 inputs.
Foreign Currency Translation	Foreign Currency Translation The Company considers the U.S. dollar to be its functional currency. Expenses denominated in foreign currencies are translated at the exchange rate on the date the expense is incurred. The effect of exchange rate fluctuations on translating foreign currency assets and liabilities into U.S. dollars is included in the Consolidated Statements of Operations and Comprehensive Loss. Foreign exchange transaction gains and losses are included in the results of operations and are not material in the Company's financial statements.
Income Taxes	Income Taxes The Company utilizes the liability method of accounting for deferred income taxes, as set forth in ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the carrying amounts and the tax basis of assets and liabilities. A valuation allowance is established against deferred tax assets when, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company's policy is to record interest and penalties on uncertain tax positions as income tax expense.
Leases	Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, it recognizes a right-of-use ("ROU") asset and operating lease liability on the Company's Consolidated Balance Sheet. ROU assets represent the Company's right to use the underlying asset for the lease term and the lease obligation represents the Company's commitment to make the lease payments arising from the lease. Right-of-use lease assets and obligations are recognized at the commencement date based on the present value of remaining lease payments over the lease term. As the Company’s leases do not provide an implicit discount rate, the Company has used an estimated incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. ROU assets include any lease payments made prior to commencement and excludes any lease incentives. The lease term may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term, subject to any changes in the lease or expectations regarding the terms. Variable lease costs such as common area costs and property taxes are expensed as incurred. For all office lease agreements the Company combines lease and nonlease components. Leases with an initial term of 12 months or less are not recorded on the Company's Consolidated Balance Sheet.
Property and Equipment	Property and Equipment Property and equipment, which consists mainly of clinical equipment, laboratory equipment, computers, software, other office equipment, automobiles and leasehold improvements, are carried at cost less accumulated depreciation. Depreciation is computed over the estimated useful lives of the respective assets, generally three to ten years, using the straight-line method. Amortization of leasehold improvements is recorded over the shorter of the lease term or estimated useful life of the related asset.
Research and Development	Research and Development The Company's research and development expenses primarily consist of costs associated with the manufacturing, development, and preclinical and clinical testing of the Company's product candidates and costs associated with its gene therapy research programs. The Company's research and development expenses consist of: •external research and development expenses incurred under arrangements with third parties, such as contract research organizations ("CROs") and contract development and manufacturing organizations ("CDMOs") and other vendors for the production and analysis of drug substance and drug product; and •employee-related expenses for employees dedicated to research and development activities, including salaries, benefits and share-based compensation expense. Research and development expenses also include costs of acquired product licenses, in-process research and development, and related technology rights where there is no alternative future use, costs of prototypes used in research and development, consultant fees and amounts paid to collaborators. All research and development expenses are charged to operations as incurred in accordance with ASC 730, Research and Development. The Company accounts for non-refundable advance payments for goods and services that will be used in future research and development activities as expenses when the service has been performed or when the goods have been received, rather than when the payment is made.
Share-Based Compensation	Share-Based Compensation The Company follows the provisions of ASC 718, Compensation—Stock Compensation, which requires the measurement and recognition of compensation expense for all share-based payment awards made to employees, non-employee directors and certain other individuals, including employee stock options, restricted stock units (“RSUs”) and options granted to employees to purchase shares under the 2016 Employee Stock Purchase Plan (the “ESPP”). Share-based compensation expense is based on the grant date fair value estimated in accordance with the provisions of ASC 718 and is generally recognized as an expense over the requisite service period, net of estimated forfeitures. For grants containing performance-based vesting provisions, expense is recognized over the estimated achievement period only when the performance-based milestone is deemed probable of achievement. If performance-based milestones are later determined not to be probable of achievement, then all previously recorded stock-based compensation expense associated with such options will be reversed during the period in which the Company makes this determination. For grants containing a market condition, the Company estimated the fair value using a Monte Carlo simulation model which takes into consideration different stock price paths. The Company recognizes compensation expense for the market award on a straight-line basis over the derived service period. Compensation expense is recognized for market awards, so long as the requisite service is provided. The Company estimates forfeitures at the time of grant and revises those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate pre-vesting forfeitures and record share-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company's estimates, the difference is recorded as a cumulative adjustment in the period the estimates were revised.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements The Company has evaluated recent accounting pronouncements through the date the financial statements were issued and filed with the SEC and believes that there are none that will have a material impact on the Company’s financial statements.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

Basis of Presentation and Consolidation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.

Basis of Consolidation

The consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Segment and geographic information

Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment.

Use of Estimates

The preparation of financial statements and related disclosures in conformity with GAAP requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. The Company bases its estimates and judgments on historical experience and on various other assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company's Consolidated Balance Sheets and the amount of expenses reported for each of the periods presented are affected by estimates and assumptions, which are used for, but not limited to, accounting for research and development costs and accounting for share-based compensation. Actual results could differ from those estimates.

Cash and Cash Equivalents

Cash and Cash Equivalents and Available-for-Sale Securities

The Company considers all highly liquid investments with an original maturity of 90 days or less when purchased to be cash equivalents. The carrying amounts reported in the Company's Consolidated Balance Sheets for cash and cash equivalents are valued at cost, which approximates their fair value.

Available-for-Sale Securities

The Company considers debt securities with original maturities of greater than 90 days to be available-for-sale securities. Available-for-sale securities with original maturities of greater than one year are recorded as non-current assets. Available-for-sale securities are recorded at fair value and unrealized gains and losses are recorded within other comprehensive income.

On a quarterly basis, the Company reviews the status of each security in an unrealized loss position, to evaluate the existence of potential credit losses. The Company first considers whether it intends to sell, or if it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through income. For securities that do not meet this criteria, the Company considers a number of factors to determine if the decline in fair value has resulted from credit losses or other factors, including but not limited to: (1) the extent of the decline; (2) changes to the rating of the security by a rating agency; (3) any adverse conditions specific to the security; and (4) other market conditions that may affect the fair value of the security. If this assessment indicates that a credit loss exists and the present value of cash flows expected to be collected is less than the amortized cost basis, an allowance for credit losses is required for the credit loss. Any impairment that has not been recorded through an allowance for credit losses is recognized in other comprehensive income.

Concentration of Credit Risk

The Company's financial instruments that are exposed to concentration of credit risk consist primarily of cash, cash equivalents and available-for-sale securities. The Company maintains its cash in bank accounts, the balances of which generally exceed federally insured limits. The Company maintains its cash equivalents and available-for-sale securities in investments in money market funds, in U.S. Treasury securities, U.S. Government Agency securities, investment-grade corporate debt securities, asset-backed securities and debt instruments issued by foreign governments with original maturities of 90 days or less.

The Company believes it is not exposed to significant credit risk on its cash, cash equivalents and available-for-sale securities.

Concentration of Suppliers

The Company historically relied upon a single third-party manufacturer to provide the drug substance for ACP on a purchase order basis. The Company also historically relied upon a single third-party manufacturer to provide fill/finish services for clinical supplies of ACP. The Company has engaged one additional third-party manufacturer to provide drug substance for ACP and one additional third-party manufacturer to provide fill/finish services for clinical supplies of ACP. In addition, the Company currently relies upon a single third-party supplier to supply on a purchase order basis the polyethylene glycol starting material used to manufacture ACP. Furthermore, the Company and its contract manufacturers currently rely upon sole-source suppliers of certain raw materials and other specialized components of production used in the manufacture and fill/finish of ACP. The Company currently relies upon a single third-party contract manufacturer to provide the drug substance for IC-500 for preclinical toxicology studies and early-stage clinical trials and a single third-party contract manufacturer to conduct fill/finish services for IC-500 drug product. If the Company’s third-party manufacturers or fill/finish service providers should become unavailable to the Company for any reason, including as a result of capacity constraints, different business objectives, financial difficulties, insolvency or the impact of COVID-19, the Company believes that there are a limited number of potential replacement manufacturers, and the Company likely would incur added costs and delays in identifying or qualifying such replacements.

Equity Investments

The Company holds investments in equity securities without a readily determinable fair value. Equity investments without a readily determinable fair value are recognized at fair value and are adjusted for observable price changes, or when qualitative assessments indicate that impairment exists, which is recorded in other income (loss).

Financial Instruments

Cash equivalents are reflected in the accompanying financial statements at fair value. The carrying amount of accounts payable and accrued expenses, including accrued research and development expenses, approximates fair value due to the short-term nature of those instruments. The carrying amount of the Company's term loan approximates fair value due to the variable interest rate nature of the debt.

Accounting Standards Codification, or ASC 820, Fair Value Measurements and Disclosures, defines fair value as the price that would be received to sell an asset, or paid to transfer a liability, in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. The fair value standard also establishes a three-level hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value.

The Company reviews investments on a periodic basis for other than temporary impairments. This review is subjective as it requires management to evaluate whether an event or change in circumstances has occurred in the period that may have a significant adverse effect on the fair value of the investment. The Company uses the market approach to measure fair value for its cash, cash equivalents and available-for-sale financial assets. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability on the measurement date. The three levels are defined as follows:

•Level 1—inputs to the valuation methodology are quoted prices (unadjusted) for an identical asset or liability in an active market. The Company's Level 1 assets consist of investments in money market funds and U.S. Treasury securities.

•Level 2—inputs to the valuation methodology include quoted prices for a similar asset or liability in an active market or model-derived valuations in which all significant inputs are observable for substantially the full term of the asset or liability. The Company's Level 2 assets consist of investments in investment-grade corporate debt securities.

•Level 3—inputs to the valuation methodology are unobservable and significant to the fair value measurement of the asset or liability. The Company does not hold any assets that are measured using Level 3 inputs.

Foreign Currency Translation

The Company considers the U.S. dollar to be its functional currency. Expenses denominated in foreign currencies are translated at the exchange rate on the date the expense is incurred. The effect of exchange rate fluctuations on translating foreign currency assets and liabilities into U.S. dollars is included in the Consolidated Statements of Operations and Comprehensive Loss. Foreign exchange transaction gains and losses are included in the results of operations and are not material in the Company's financial statements.

Income Taxes

The Company utilizes the liability method of accounting for deferred income taxes, as set forth in ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the carrying amounts and the tax basis of assets and liabilities. A valuation allowance is established against deferred tax assets when, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company's policy is to record interest and penalties on uncertain tax positions as income tax expense.

Leases

The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, it recognizes a right-of-use ("ROU") asset and operating lease liability on the Company's Consolidated Balance Sheet. ROU assets represent the Company's right to use the underlying asset for the lease term and the lease obligation represents the Company's commitment to make the lease payments arising from the lease. Right-of-use lease assets and obligations are recognized at the commencement date based on the present value of remaining lease payments over the lease term. As the Company’s leases do not provide an implicit discount rate, the Company has used an estimated incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. ROU assets include any lease payments made prior to commencement and excludes any lease incentives. The lease term may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term, subject to any changes in the lease or expectations regarding the terms. Variable lease costs such as common area costs and property taxes are expensed as incurred. For all office lease agreements the Company combines lease and nonlease components. Leases with an initial term of 12 months or less are not recorded on the Company's Consolidated Balance Sheet.

Property and Equipment

Property and equipment, which consists mainly of clinical equipment, laboratory equipment, computers, software, other office equipment, automobiles and leasehold improvements, are carried at cost less accumulated depreciation. Depreciation is computed over the estimated useful lives of the respective assets, generally three to ten years, using the straight-line method. Amortization of leasehold improvements is recorded over the shorter of the lease term or estimated useful life of the related asset.

Research and Development

The Company's research and development expenses primarily consist of costs associated with the manufacturing, development, and preclinical and clinical testing of the Company's product candidates and costs associated with its gene therapy research programs. The Company's research and development expenses consist of:

•external research and development expenses incurred under arrangements with third parties, such as contract research organizations ("CROs") and contract development and manufacturing organizations ("CDMOs") and other vendors for the production and analysis of drug substance and drug product; and

•employee-related expenses for employees dedicated to research and development activities, including salaries, benefits and share-based compensation expense.

Research and development expenses also include costs of acquired product licenses, in-process research and development, and related technology rights where there is no alternative future use, costs of prototypes used in research and development, consultant fees and amounts paid to collaborators.

All research and development expenses are charged to operations as incurred in accordance with ASC 730, Research and Development. The Company accounts for non-refundable advance payments for goods and services that will be used in future research and development activities as expenses when the service has been performed or when the goods have been received, rather than when the payment is made.

Share-Based Compensation

The Company follows the provisions of ASC 718, Compensation—Stock Compensation, which requires the measurement and recognition of compensation expense for all share-based payment awards made to employees, non-employee directors and certain other individuals, including employee stock options, restricted stock units (“RSUs”) and options granted to employees to purchase shares under the 2016 Employee Stock Purchase Plan (the “ESPP”). Share-based compensation expense is based on the grant date fair value estimated in accordance with the provisions of ASC 718 and is generally recognized as an expense over the requisite service period, net of estimated forfeitures. For grants containing performance-based vesting provisions, expense is recognized over the estimated achievement period only when the performance-based milestone is deemed probable of achievement. If performance-based milestones are later determined not to be probable of achievement,

then all previously recorded stock-based compensation expense associated with such options will be reversed during the period in which the Company makes this determination. For grants containing a market condition, the Company estimated the fair value using a Monte Carlo simulation model which takes into consideration different stock price paths. The Company recognizes compensation expense for the market award on a straight-line basis over the derived service period. Compensation expense is recognized for market awards, so long as the requisite service is provided.

The Company estimates forfeitures at the time of grant and revises those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate pre-vesting forfeitures and record share-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company's estimates, the difference is recorded as a cumulative adjustment in the period the estimates were revised.

Recently Adopted Accounting Pronouncements

The Company has evaluated recent accounting pronouncements through the date the financial statements were issued and filed with the SEC and believes that there are none that will have a material impact on the Company’s financial statements.