republic services , inc . notes to consolidated financial statements 2014 ( continued ) high quality financial institutions . such balances may be in excess of fdic insured limits . to manage the related credit exposure , we continually monitor the credit worthiness of the financial institutions where we have deposits . concentrations of credit risk with respect to trade accounts receivable are limited due to the wide variety of customers and markets in which we provide services , as well as the dispersion of our operations across many geographic areas . we provide services to commercial , industrial , municipal and residential customers in the united states and puerto rico . we perform ongoing credit evaluations of our customers , but do not require collateral to support customer receivables . we establish an allowance for doubtful accounts based on various factors including the credit risk of specific customers , age of receivables outstanding , historical trends , economic conditions and other information . no customer exceeded 5% ( 5 % ) of our outstanding accounts receivable balance at december 31 , 2012 and 2011 . accounts receivable , net of allowance for doubtful accounts accounts receivable represent receivables from customers for collection , transfer , recycling , disposal and other services . our receivables are recorded when billed or when the related revenue is earned , if earlier , and represent claims against third parties that will be settled in cash . the carrying value of our receivables , net of the allowance for doubtful accounts , represents their estimated net realizable value . provisions for doubtful accounts are evaluated on a monthly basis and are recorded based on our historical collection experience , the age of the receivables , specific customer information and economic conditions . we also review outstanding balances on an account-specific basis . in general , reserves are provided for accounts receivable in excess of ninety days old . past due receivable balances are written-off when our collection efforts have been unsuccessful in collecting amounts the following table reflects the activity in our allowance for doubtful accounts for the years ended december 31 , 2012 , 2011 and 2010: .
what was the change in the allowance for doubtful accounts in 2012
restricted cash and marketable securities as of december 31 , 2012 , we had $ 164.2 million of restricted cash and marketable securities . we obtain funds through the issuance of tax-exempt bonds for the purpose of financing qualifying expenditures at our landfills , transfer stations , collection and recycling centers . the funds are deposited directly into trust accounts by the bonding authorities at the time of issuance . as the use of these funds is contractually restricted , and we do not have the ability to use these funds for general operating purposes , they are classified as restricted cash and marketable securities in our consolidated balance sheets . in the normal course of business , we may be required to provide financial assurance to governmental agencies and a variety of other entities in connection with municipal residential collection contracts , closure or post- closure of landfills , environmental remediation , environmental permits , and business licenses and permits as a financial guarantee of our performance . at several of our landfills , we satisfy financial assurance requirements by depositing cash into restricted trust funds or escrow accounts. .