deductions for stock compensation. The adoption on January 1, 2017, of ASU 2016-09 will subject our tax rate to quarterly volatility from the effect of stock award exercises and vesting activities.
Seasonal factors cause our profitability to fluctuate from quarter to quarter. Historically, our average daily restaurant sales are lower and net income has generally been lower in the first and fourth quarters due, in part, to the holiday season and because fewer people eat out during periods of inclement weather (the winter months) than during periods of mild or warm weather (the spring, summer and fall months). Other factors also have a seasonal effect on our results. For example, restaurants located near colleges and universities generally do more business during the academic year. Seasonal factors, however, might be moderated or outweighed by other factors that may influence our quarterly results, such as unexpected publicity impacting our business in a positive or negative way, as well as fluctuations in food or packaging costs or the timing of menu price increases. The number of trading days in a quarter can also affect our results, although, on an overall annual basis, changes in trading days do not have a significant impact.
Our quarterly results are also affected by other factors such as the amount and timing of non-cash stock-based compensation expense, the number of new restaurants opened in a quarter, and anticipated and unanticipated events. New restaurants typically have lower margins following opening as a result of the expenses associated with opening new restaurants and their operating inefficiencies in the months immediately following opening. Accordingly, results for a particular quarter are not necessarily indicative of results to be expected for any other quarter or for any year.
Liquidity and Capital Resources
Our primary liquidity and capital requirements are for new restaurant construction, working capital and general corporate needs. As of September 30, 2017, we had a cash and short-term investment balance of $548.4 million that we expect to utilize, along with cash flow from operations, to provide capital to support the growth of our business (primarily through opening restaurants), to repurchase additional shares of our common stock subject to market conditions, to maintain our existing restaurants and for general corporate purposes. As of September 30, 2017, $95.4 million remained available under previously-announced repurchase authorizations. On October 24, 2017, we announced that our Board of Directors authorized the expenditure of an additional $100 million to repurchase shares of common stock. Under the remaining repurchase authorizations, shares may be purchased from time to time in open market transactions, subject to market conditions. We believe that cash from operations, together with our cash and investment balances, will be enough to meet ongoing capital expenditures, working capital requirements and other cash needs for the foreseeable future.
We haven’t required significant working capital because customers generally pay using cash or credit and debit cards and because our operations do not require significant receivables, nor do they require significant inventories due, in part, to our use of various fresh ingredients. In addition, we generally have the right to pay for the purchase of food, beverage and supplies some time after the receipt of those items, generally within ten days, thereby reducing the need for incremental working capital to support our growth.
Off-Balance Sheet Arrangements
As of September 30, 2017, we had no off-balance sheet arrangements or obligations.
Critical Accounting Estimates
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 had no significant changes in our critical accounting estimates since our last annual report. Our critical accounting estimates are identified and described in our annual report on Form 10-K for the year ended December 31, 2016.
ITEM 3.QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK
Commodity Price Risks
We are exposed to commodity price risks. Many of the ingredients we use to prepare our food, our packaging materials, as well as utilities to run our restaurants are commodities or ingredients that are affected by the price of other commodities, exchange rates, foreign demand, weather, seasonality, production, availability and other factors outside our control. We work closely with our suppliers and use a mix of forward pricing protocols under which we agree with our supplier on fixed prices for deliveries at some time in the future, fixed pricing protocols under which we agree on a fixed price with our supplier for the duration of that protocol, and formula pricing protocols under which the prices we pay are based on a specified formula related to the prices of the goods, such as spot prices. However, a majority of the dollar value of goods