secure the 2015 Notes or the 5,179 wireless and broadcast towers that secure the Loan, respectively, in which case we could lose such sites and the revenue associated with those assets.
As discussed above, we use our available liquidity and seek new sources of liquidity to fund capital expenditures, future growth and expansion initiatives, satisfy our distribution requirements and repay or repurchase our debt. If we determine that it is desirable or necessary to raise additional capital, we may be unable to do so, or such additional financing may be prohibitively expensive or restricted by the terms of our outstanding indebtedness. If we are unable to raise capital when our needs arise, we may not be able to fund capital expenditures, future growth and expansion initiatives, satisfy our REIT distribution requirements and debt service obligations, pay preferred stock dividends or refinance our existing indebtedness.
In addition, our liquidity depends on our ability to generate cash flow from operating activities. As set forth under the caption “Risk Factors” in Item 1A of the 2016 Form 10-K, we derive a substantial portion of our revenues from a small number of tenants and, consequently, a failure by a significant tenant to perform its contractual obligations to us could adversely affect our cash flow and liquidity.
For more information regarding the terms of our outstanding indebtedness, please see note 8 to our consolidated financial statements included in the 2016 Form 10-K.
Critical Accounting Policies and Estimates
Management’s discussion and analysis of financial condition and results of operations are based upon our consolidated and condensed consolidated financial statements, which have been prepared in accordance with GAAP. The preparation of these financial statements requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosures of contingent assets and liabilities. We evaluate our policies and estimates on an ongoing basis, including those related to impairment of long-lived assets, asset retirement obligations, revenue recognition, rent expense, stock-based compensation, income taxes and accounting for business combinations and acquisitions of assets, which we discussed in the 2016 Form 10-K. Management bases its estimates on historical experience and various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying amounts of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions.
We have reviewed our policies and estimates to determine our critical accounting policies for the nine months ended September 30, 2017. We have made no material changes to the critical accounting policies described in the 2016 Form 10-K.
Accounting Standards Update
For a discussion of recent accounting standards updates, see note 1 to our consolidated and condensed consolidated financial statements included in this Quarterly Report on Form 10-Q.