Summary of Significant Accounting Policies	6 Months Ended
Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies In addition to the policies below, our significant accounting policies are described in Note 2 of the Notes to Consolidated Financial Statements included in our 2018 Form 10-K. There were no changes to these policies during the three and six months ended June 30, 2019. Concentration of Risks We are subject to credit risk from our portfolio of cash, cash equivalents and marketable securities. Under our investment policy, we limit amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. Cash is held at major banks in the United States. Therefore, the Company is not exposed to any significant concentrations of credit risk from these financial instruments. The goals of our investment policy, in order of priority, are as follows: safety and preservation of principal and diversification of risk, liquidity of investments sufficient to meet cash flow requirements, and a competitive after-tax rate of return. Share-Based Compensation The Company expenses all share-based payment awards to employees, directors, and consultants, including grants of stock options, warrants, and restricted stock, over the requisite service period based on the grant date fair value of the awards. Consultant awards are remeasured each reporting period through vesting. For awards with performance-based vesting criteria, the Company estimates the probability of achievement of the performance criteria and recognizes compensation expense related to those awards expected to vest. The Company determines the fair value of option awards using the Black-Scholes option-pricing model, which uses both historical and current market data to estimate the fair value. This method incorporates various assumptions such as the risk-free interest rate, expected volatility, expected dividend yield and expected life of the options or warrants. The fair value of the Company’s restricted stock and restricted stock units is based on the closing market price of the Company’s common stock on the date of grant. Income Taxes The Company recognizes (a) the amount of taxes payable or refundable for the current year and (b) deferred tax liabilities and assets for the future tax consequences of events that have been recognized in the Company’s financial statements or tax returns. The Company evaluates the accounting for uncertainty in tax positions at the end of each reporting period. The accounting guidance requires companies to recognize in their financial statements the impact of a tax position if the position is more likely than not to be sustained if the position were to be challenged by a taxing authority. The position ascertained inherently requires judgment and estimates by management. The Company recognizes interest and penalties as a component of income tax expense. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). This ASU requires that a lessee recognize lease assets and lease liabilities for those leases classified as operating leases. The guidance was effective for interim and annual periods beginning after December 15, 2018 and was adopted as of January 1, 2019. The Company adopted the standard using the optional transition method, with an immaterial adjustment to accumulated deficit upon adoption. The comparative information has not been restated and continues to be reported under the accounting standards that were in effect for those periods. The Company concluded that the adoption of ASU 2016-02 was non-cash in nature, did not affect the Company's cash position, and did not have a material impact on the Company's financial statements. In June 2018, the FASB issued ASU No. 2018-07, "Improvements to Nonemployee Share-Based Payment Accounting", which supersedes ASC 505-50 and expands the scope of ASC 718 to include all share-based payments arrangements related to the acquisition of goods and services from both employees and nonemployees. For public companies, the amendments are effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual periods. Early adoption is permitted, but no earlier than a company's adoption date of ASC 606. The Company determined that the adoption of this new accounting guidance did not have a material impact on its financial statements and footnote disclosures.

Summary of Significant Accounting Policies

In addition to the policies below, our significant accounting policies are described in Note 2 of the Notes to Consolidated Financial Statements included in our 2018 Form 10-K. There were no changes to these policies during the three and six months ended June 30, 2019.

Concentration of Risks

We are subject to credit risk from our portfolio of cash, cash equivalents and marketable securities. Under our investment policy, we limit amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. Cash is held at major banks in the United States. Therefore, the Company is not exposed to any significant concentrations of credit risk from these financial instruments. The goals of our investment policy, in order of priority, are as follows: safety and preservation of principal and diversification of risk, liquidity of investments sufficient to meet cash flow requirements, and a competitive after-tax rate of return.

Share-Based Compensation

The Company expenses all share-based payment awards to employees, directors, and consultants, including grants of stock options, warrants, and restricted stock, over the requisite service period based on the grant date fair value of the awards. Consultant awards are remeasured each reporting period through vesting. For awards with performance-based vesting criteria, the Company estimates the probability of achievement of the performance criteria and recognizes compensation expense related to those awards expected to vest. The Company determines the fair value of option awards using the Black-Scholes option-pricing model, which uses both historical and current market data to estimate the fair value. This method incorporates various assumptions such as the risk-free interest rate, expected volatility, expected dividend yield and expected life of the options or warrants. The fair value of the Company’s restricted stock and restricted stock units is based on the closing market price of the Company’s common stock on the date of grant.

Income Taxes

The Company recognizes (a) the amount of taxes payable or refundable for the current year and (b) deferred tax liabilities and assets for the future tax consequences of events that have been recognized in the Company’s financial statements or tax returns.

The Company evaluates the accounting for uncertainty in tax positions at the end of each reporting period. The accounting guidance requires companies to recognize in their financial statements the impact of a tax position if the position is more likely than not to be sustained if the position were to be challenged by a taxing authority. The position ascertained inherently requires judgment and estimates by management. The Company recognizes interest and penalties as a component of income tax expense.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). This ASU requires that a lessee recognize lease assets and lease liabilities for those leases classified as operating leases. The guidance was effective for interim and annual periods beginning after December 15, 2018 and was adopted as of January 1, 2019. The Company adopted the standard using the optional transition method, with an immaterial adjustment to accumulated deficit upon adoption. The comparative information has not been restated and continues to be reported under the accounting standards that were in effect for those periods. The Company concluded that the adoption of ASU 2016-02 was non-cash in nature, did not affect the Company's cash position, and did not have a material impact on the Company's financial statements.

In June 2018, the FASB issued ASU No. 2018-07, "Improvements to Nonemployee Share-Based Payment Accounting", which supersedes ASC 505-50 and expands the scope of ASC 718 to include all share-based payments arrangements related to the acquisition of goods and services from both employees and nonemployees. For public companies, the amendments are effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual periods. Early adoption is permitted, but no earlier than a company's adoption date of ASC 606. The Company determined that the adoption of this new accounting guidance did not have a material impact on its financial statements and footnote disclosures.