SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The accompanying condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company has experienced net losses and negative cash flows from operating activities since its inception. At March 31, 2018, the Company had an accumulated deficit of $166.1 million. The Company expects to continue to incur net losses into the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. In accordance with ASU 2014-15, management is required to perform a two-step analysis over its ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company's ability to continue as a going concern (step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (step 2). The evaluation period is through one year beyond the date the financial statements were released (assumed to be through May 9, 2019). The Company has prepared cash flow forecasts which indicate, based on its current cash resources available and access to capital under its Loan Agreement with Pacific Western Bank that it will not have sufficient resources to fund its business, including its ongoing clinical trials, for at least the next 12 months from the date of this filing. The Company will need to raise additional capital to fund its losses from operations. It anticipates raising capital through debt and equity financing, through government funding or through collaborations or partnerships with other entities. Debt or equity financing, government funding or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all. If the Company is not able to secure adequate additional funding, the Company may be forced to delay, reduce or eliminate its research and development programs or future commercialization efforts, or to make reductions in spending, extend payment terms with suppliers, liquidate or grant rights to assets where possible, or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations and future prospects. Management has developed a plan to implement cost cutting measures to reduce its working capital requirements over the next 12 months if an adequate level of financing is not secured. The plan includes the delay of certain of the Company’s development activities, a delay in hiring and a reduction of other discretionary expenditures that are within the Company’s control. Any of the actions contemplated by the implementation of this plan, if required, could have an adverse impact on the Company’s ability to achieve certain of its planned objectives during 2018, and thus, materially harm the Company’s business.
Unaudited Interim Financial Data	Unaudited Interim Financial Data The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with U.S. generally accepted accounting principles, or GAAP, as found in the Accounting Standards Codification, or ASC, of the Financial Accounting Standards Board, or FASB. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended March 31, 2018 and 2017.
Basis of Consolidation	Basis of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s stock options and certain accruals, including those related to nonclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Segment Information	Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.
Cash, and Cash Equivalents, and Restricted Cash	Cash, and Cash Equivalents, and Restricted Cash The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents. Restricted cash represents cash held in a segregated bank account related to a commercial letter of credit to facilitate payment to a foreign supplier.
Investments Available-for-Sale	Investments Available-for-Sale Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive loss. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Securities with maturity dates of 12 months or less from the date of purchase are classified as short-term investments and securities with maturity dates of more than 12 months are classified as long-term investments.
Concentration of Credit Risk	Concentration of Credit Risk The Company’s financial instruments that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. Periodically, the Company maintains deposits in government insured financial institutions in excess of government insured limits. The Company invests its cash balances in financial institutions that it believes have high credit quality, has not experienced any losses on such accounts and does not believe it is exposed to significant credit risk.
Patent Costs	Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications), and such costs are included in general and administrative expenses in the accompanying statements of operations.
Income Taxes	Income Taxes The Company follows the FASB's ASC 740, Income Taxes, in reporting deferred income taxes. ASC 740 requires a company to recognize deferred tax assets and liabilities for expected future income tax consequences of events that have been recognized in the Company’s consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates in the years in which the temporary differences are expected to reverse. Valuation allowances are provided if, 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 accounts for uncertain tax positions pursuant to ASC 740, which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured as the tax benefit having the highest likelihood of being realized upon ultimate settlement with the taxing authority. The Company recognizes interest accrued related to unrecognized tax benefits and penalties in the provision for income taxes. On December 22, 2017, the U.S. enacted the Tax Cuts and Jobs Act (the "Tax Act"), which among other provisions, reduced the U.S. corporate tax rate from 35% to 21%, effective January 1, 2018. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, the Company made reasonable estimates of the effects and recorded provisional amounts in our financial statements as of December 31, 2017. As the Company collects and prepares necessary data, and continues to interpret the Tax Act and any additional guidance issued by the U.S. Treasury Department, the Internal Revenue Service (IRS) and other standard-setting bodies, the Company may make adjustments to the provisional amounts. Those adjustments may affect deferred tax balances. However, due to the valuation allowance position, the Company expects there will be no net impact to the financial statements. The Company did not make any such adjustments during the quarter ended March 31, 2018. Any adjustments to account for the tax effects of the Tax Act would be made in a subsequent quarter.
Revenue Recognition	Revenue Recognition The Company recognizes revenues when customers obtain control of promised goods or services, in an amount that reflects the consideration which we expect to receive in exchange for those goods or services. We recognize revenues following the five step model prescribed under Accounting Standards Update ("ASU") No. 2014-09 ("ASU 2014-09"): (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) we satisfy the performance obligation. Under the Subaward Agreement, the Company is reimbursed for direct costs incurred plus allowable indirect costs which consist of fringe benefits and allowable general and administrative expenses.
Grant Funding and Research and Development Costs	Grant Funding The Company has received research and development funding through a grant from CARB-X, a public-private partnership focused on antibacterials. The Company has evaluated the terms of the grant to assess its obligations and the classification of funding received. Amounts billable for funded research and development are recognized in the statement of operations as a reduction to research and development expense over the grant period as the related costs are incurred to meet the Company's obligations. Research and Development Costs Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and nonclinical and clinical trial costs. The Company accrues nonclinical and clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies, and other events. Costs incurred in purchasing technology assets and intellectual property are charged to research and development expense if the technology has not been conclusively proven to be feasible and has no alternative future use.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized losses on marketable securities. Comprehensive losses have been reflected in the condensed consolidated statements of operations and comprehensive loss for all periods presented.
Stock-based Compensation	Stock-based Compensation The Company accounts for stock-based compensation expense related to employee stock options and employee stock purchase plan rights by estimating the fair value on the date of grant using the Black-Scholes option pricing model. The fair value of Restricted Stock Units (RSUs) and Performance-based RSUs (PRSUs) granted to employees is estimated based on the closing price of the Company's common stock on the date of grant. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. For awards subject to performance-based vesting conditions, the Company assesses the probability of achievement of the individual milestones under the stock-based awards and recognizes stock-based compensation expense over the implicit service period commencing once the Company believes the performance criteria is probable of achievement. The Company accounts for stock options, RSUs, and PRSUs granted to non-employees using the fair value approach. These stock-based awards are subject to periodic revaluation over their vesting terms.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of unvested restricted common stock subject to repurchase, warrants, and RSUs and options outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company follows ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques, such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, restricted cash, marketable securities, and long-term debt. Fair value estimates of these instruments are made at a specific point in time based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, restricted cash, prepaid expenses, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The fair value of short-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company believes that the fair value of long-term debt approximates its carrying value.
Recently Issued Accounting Standards	Recently Issued Accounting Standards Recently Issued Accounting Standards Not Yet Adopted During 2016, the FASB issued ASU 2016-02, “Leases,” which requires that operating lease arrangements longer than 12 months result in an entity recognizing an asset and liability. The updated guidance is effective for interim and annual periods beginning after December 15, 2018, and early adoption is permitted. The Company currently expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon the adoption of ASU 2016-02, which will increase the total assets and total liabilities that it reports relative to such amounts prior to adoption. Recently Adopted Accounting Standards During 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Numerous ASUs were issued in 2016 and 2017 to require additional disclosures, to provide clarification on a number of specific issues pertaining to ASU 2014-09, and to defer the effective date for ASU 2014-09 to interim and annual periods beginning after December 31, 2017. The Company adopted ASC 606 effective January 1, 2018. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

3 Months Ended

Mar. 31, 2018

The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The accompanying condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company has experienced net losses and negative cash flows from operating activities since its inception. At March 31, 2018, the Company had an accumulated deficit of $166.1 million. The Company expects to continue to incur net losses into the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure.

In accordance with ASU 2014-15, management is required to perform a two-step analysis over its ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company's ability to continue as a going concern (step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (step 2). The evaluation period is through one year beyond the date the financial statements were released (assumed to be through May 9, 2019).

The Company has prepared cash flow forecasts which indicate, based on its current cash resources available and access to capital under its Loan Agreement with Pacific Western Bank that it will not have sufficient resources to fund its business, including its ongoing clinical trials, for at least the next 12 months from the date of this filing.

The Company will need to raise additional capital to fund its losses from operations. It anticipates raising capital through debt and equity financing, through government funding or through collaborations or partnerships with other entities. Debt or equity financing, government funding or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all. If the Company is not able to secure adequate additional funding, the Company may be forced to delay, reduce or eliminate its research and development programs or future commercialization efforts, or to make reductions in spending, extend payment terms with suppliers, liquidate or grant rights to assets where possible, or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations and future prospects.

Management has developed a plan to implement cost cutting measures to reduce its working capital requirements over the next 12 months if an adequate level of financing is not secured. The plan includes the delay of certain of the Company’s development activities, a delay in hiring and a reduction of other discretionary expenditures that are within the Company’s control. Any of the actions contemplated by the implementation of this plan, if required, could have an adverse impact on the Company’s ability to achieve certain of its planned objectives during 2018, and thus, materially harm the Company’s business.

Unaudited Interim Financial Data

The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with U.S. generally accepted accounting principles, or GAAP, as found in the Accounting Standards Codification, or ASC, of the Financial Accounting Standards Board, or FASB. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended March 31, 2018 and 2017.

Basis of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All significant intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s stock options and certain accruals, including those related to nonclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.

Segment Information

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.

Cash, and Cash Equivalents, and Restricted Cash

The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents.

Restricted cash represents cash held in a segregated bank account related to a commercial letter of credit to facilitate payment to a foreign supplier.

Investments Available-for-Sale

Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive loss. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Securities with maturity dates of 12 months or less from the date of purchase are classified as short-term investments and securities with maturity dates of more than 12 months are classified as long-term investments.

Concentration of Credit Risk

The Company’s financial instruments that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. Periodically, the Company maintains deposits in government insured financial institutions in excess of government insured limits. The Company invests its cash balances in financial institutions that it believes have high credit quality, has not experienced any losses on such accounts and does not believe it is exposed to significant credit risk.

Patent Costs

The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications), and such costs are included in general and administrative expenses in the accompanying statements of operations.

Income Taxes

The Company follows the FASB's ASC 740, Income Taxes, in reporting deferred income taxes. ASC 740 requires a company to recognize deferred tax assets and liabilities for expected future income tax consequences of events that have been recognized in the Company’s consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates in the years in which the temporary differences are expected to reverse. Valuation allowances are provided if, 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 accounts for uncertain tax positions pursuant to ASC 740, which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured as the tax benefit having the highest likelihood of being realized upon ultimate settlement with the taxing authority. The Company recognizes interest accrued related to unrecognized tax benefits and penalties in the provision for income taxes.

On December 22, 2017, the U.S. enacted the Tax Cuts and Jobs Act (the "Tax Act"), which among other provisions, reduced the U.S. corporate tax rate from 35% to 21%, effective January 1, 2018. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, the Company made reasonable estimates of the effects and recorded provisional amounts in our financial statements as of December 31, 2017. As the Company collects and prepares necessary data, and continues to interpret the Tax Act and any additional guidance issued by the U.S. Treasury Department, the Internal Revenue Service (IRS) and other standard-setting bodies, the Company may make adjustments to the provisional amounts. Those adjustments may affect deferred tax balances. However, due to the valuation allowance position, the Company expects there will be no net impact to the financial statements. The Company did not make any such adjustments during the quarter ended March 31, 2018. Any adjustments to account for the tax effects of the Tax Act would be made in a subsequent quarter.

Revenue Recognition

The Company recognizes revenues when customers obtain control of promised goods or services, in an amount that reflects the consideration which we expect to receive in exchange for those goods or services. We recognize revenues following the five step model prescribed under Accounting Standards Update ("ASU") No. 2014-09 ("ASU 2014-09"): (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) we satisfy the performance obligation.

Under the Subaward Agreement, the Company is reimbursed for direct costs incurred plus allowable indirect costs which consist of fringe benefits and allowable general and administrative expenses.

Grant Funding and Research and Development Costs

Grant Funding

The Company has received research and development funding through a grant from CARB-X, a public-private partnership focused on antibacterials. The Company has evaluated the terms of the grant to assess its obligations and the classification of funding received. Amounts billable for funded research and development are recognized in the statement of operations as a reduction to research and development expense over the grant period as the related costs are incurred to meet the Company's obligations.

Research and Development Costs

Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and nonclinical and clinical trial costs. The Company accrues nonclinical and clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies, and other events.

Costs incurred in purchasing technology assets and intellectual property are charged to research and development expense if the technology has not been conclusively proven to be feasible and has no alternative future use.

Comprehensive Loss

Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized losses on marketable securities. Comprehensive losses have been reflected in the condensed consolidated statements of operations and comprehensive loss for all periods presented.

Stock-based Compensation

The Company accounts for stock-based compensation expense related to employee stock options and employee stock purchase plan rights by estimating the fair value on the date of grant using the Black-Scholes option pricing model. The fair value of Restricted Stock Units (RSUs) and Performance-based RSUs (PRSUs) granted to employees is estimated based on the closing price of the Company's common stock on the date of grant. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. For awards subject to performance-based vesting conditions, the Company assesses the probability of achievement of the individual milestones under the stock-based awards and recognizes stock-based compensation expense over the implicit service period commencing once the Company believes the performance criteria is probable of achievement. The Company accounts for stock options, RSUs, and PRSUs granted to non-employees using the fair value approach. These stock-based awards are subject to periodic revaluation over their vesting terms.

Net Loss Per Share

Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of unvested restricted common stock subject to repurchase, warrants, and RSUs and options outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding.

Fair Value of Financial Instruments

The Company follows ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques, such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels.

The Company’s financial instruments consist of cash and cash equivalents, restricted cash, marketable securities, and long-term debt. Fair value estimates of these instruments are made at a specific point in time based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, restricted cash, prepaid expenses, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The fair value of short-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company believes that the fair value of long-term debt approximates its carrying value.

Recently Issued Accounting Standards

Recently Issued Accounting Standards Not Yet Adopted

During 2016, the FASB issued ASU 2016-02, “Leases,” which requires that operating lease arrangements longer than 12 months result in an entity recognizing an asset and liability. The updated guidance is effective for interim and annual periods beginning after December 15, 2018, and early adoption is permitted. The Company currently expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon the adoption of ASU 2016-02, which will increase the total assets and total liabilities that it reports relative to such amounts prior to adoption.

Recently Adopted Accounting Standards

During 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Numerous ASUs were issued in 2016 and 2017 to require additional disclosures, to provide clarification on a number of specific issues pertaining to ASU 2014-09, and to defer the effective date for ASU 2014-09 to interim and annual periods beginning after December 31, 2017. The Company adopted ASC 606 effective January 1, 2018. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements.