net income growth, and total shareholder return. Our estimates of Chipotle’s future performance and the future performance of the restaurant industry peer group are assumptions that involve a high degree of subjectivity. If we had arrived at different assumptions for revenue growth or net income for Chipotle or the peer group, our stock-based compensation expense and results of operations could have been different.
We are self-insured for a significant portion of our risks and associated liabilities with respect to workers’ compensation, general liability, employee health, property and auto damage, but have third party insurance coverage to limit exposure to these claims. We record a liability that represents our estimated cost of claims incurred and unpaid as of the balance sheet date. Our estimated liability is not discounted and is based on a number of assumptions and factors, including historical trends, actuarial assumptions and economic conditions, and is closely monitored and adjusted when warranted by changing circumstances. Our history of claims experience is relatively short and our significant growth during most of our operating history could affect the accuracy of estimates based on historical experience. If a greater amount of claims occurs compared to what we have estimated, or if medical costs increase beyond what we expected, our accrued liabilities might not be sufficient and we may be required to record additional expense. Actual claims experience could also be more favorable than estimated, which would result in expense reductions. Unanticipated changes may produce materially different amounts of expense than that reported under these programs. The total estimated insurance liabilities as of December 31, 2017 were $52.0 million.
Reserves/Contingencies for Litigation and Other Matters
We are involved in various claims and legal actions that arise in the ordinary course of business. These actions are subject to many uncertainties, and we cannot predict the outcomes with any degree of certainty. Consequently, we were unable to estimate the ultimate aggregate amount of monetary liability or financial impact with respect to these matters as of December 31, 2017. Although we have recorded liabilities related to a number of legal actions, our estimates used to determine the amount of these liabilities may not be accurate, and there are other legal actions for which we have not recorded a liability. As a result, in the event legal actions for which we have not accrued a liability or for which our accrued liabilities are not accurate are resolved, such resolution may affect our operating results and cash flows.