obligations relate to amounts owed for chicken, produce, and other ingredients and supplies, construction contractor agreements, orders submitted for equipment for restaurants under construction and planned remodels, and marketing initiatives and corporate sponsorships.
The above table does not include income tax liabilities for uncertain tax positions for which we are not able to make a reasonably reliable estimate of the amount and period of related future payments. Additionally, we have excluded our estimated loss contingencies related to the data security incident described elsewhere, due to uncertainty regarding the timing and amount of payment. See Note 10. “Commitments and Contingencies” of our consolidated financial statements included in Item 8. “Financial Statements and Supplementary Data.”
Off-Balance Sheet Arrangements
As of December 31, 2017 and 2016, we had no off-balance sheet arrangements or obligations.
The primary areas of our operations affected by inflation are food, labor, healthcare costs, fuel, utility costs, and materials used in the construction of our restaurants. Although a significant majority of our crew members make more than the federal and applicable state and local minimum wage, increases in the applicable federal or state minimum wage may have an impact on our labor costs by causing wage inflation above the minimum wage level. Additionally, many of our leases require us to pay property taxes, maintenance, and utilities, all of which are generally subject to inflationary increases. In the past we have largely been able to offset inflationary increases with menu price increases. There have been, and there may be in the future, delays in implementing such menu price increases. If we do raise menu prices in the future, general competitive pressures may limit our ability to completely recover cost increases attributable to inflation.
Critical Accounting Estimates
We describe our significant accounting policies in Note 1. “Description of Business and Summary of Significant Accounting Policies” of our consolidated financial statements included in Item 8. “Financial Statements and Supplementary Data.” Critical accounting estimates are those that we believe are both significant and that require us to make difficult, subjective or complex judgments, often because we need to estimate the effect of inherently uncertain matters. We base our estimates and judgments on historical experiences and various other factors that we believe to be appropriate under the circumstances. Actual results may differ from these estimates, and we might obtain different estimates if we used different assumptions or factors. We believe that of our critical accounting estimates, the following involve a higher degree of judgement and subjectivity.
We lease nearly all of our restaurant locations. Our leases typically contain escalating rentals over the lease term as well as optional renewal periods. We have estimated that our lease term, including reasonably assured renewal periods, is the lesser of the lease term or 20 years. We account for our leases by recognizing rent expense on a straight-line basis over the reasonably assured lease term. The majority of our leasehold improvements are also depreciated over the reasonably assured lease term. If the estimate of our reasonably assured lease term was changed, our depreciation and rent expense could differ materially.
We recognize compensation expense for equity awards over the vesting period based on the award’s fair value. We use the Black-Scholes valuation model to determine the fair value of our stock-only stock appreciation rights, or SOSARs, and we use the Monte Carlo simulation model to determine the fair value of stock awards that contain market conditions. Both of these models require assumptions to be made regarding our stock price volatility, the expected life of the award and expected dividend rates. The volatility assumption was based on our historical data and implied volatility, and the expected life assumptions were based on our historical data. Similarly, the compensation expense of performance share awards, and SOSARs with performance-based vesting conditions, is based in part on the estimated probability of our achieving levels of performance associated with particular levels of payout for performance shares and with vesting for performance SOSARs. We determine the probability of achievement of future levels of performance by comparing the relevant performance level with our internal estimates of future performance. Those estimates are based on a number of assumptions, and different assumptions may have resulted in different conclusions regarding the probability of our achieving future levels of performance relevant to the payout levels for the awards. Had we arrived at different assumptions of stock price volatility or expected lives of our SOSARs, or different assumptions regarding the probability of our achieving future levels of performance with respect to performance share awards and performance SOSARs, our stock-based compensation expense and results of operations could have been different. Certain awards that contain service, performance and market conditions have vesting criteria based on Chipotle’s relative performance versus a restaurant industry peer group in annual average revenue growth,