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 small-container , large-container , municipal and residential , and energy services customers in the united states and puerto rico . we perform ongoing credit evaluations of our customers , but generally 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 . accounts receivable , net accounts receivable represent receivables from customers for collection , transfer , recycling , disposal , energy services 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 and customer credits , 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 90 days outstanding . past due receivable balances are written-off when our collection efforts have been unsuccessful in collecting amounts due . the following table reflects the activity in our allowance for doubtful accounts for the years ended december 31: .
as of december 31 , 2017 what was the ratio of restricted cash and marketable securities for the supports our insurance programs for workers 2019 compensation , commercial general liability , and commercial auto liability to the total restricted cash and marketable securities
restricted cash and marketable securities as of december 31 , 2017 , we had $ 141.1 million of restricted cash and marketable securities of which $ 71.4 million supports our insurance programs for workers 2019 compensation , commercial general liability , and commercial auto liability . additionally , 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 . property and equipment we record property and equipment at cost . expenditures for major additions and improvements to facilities are capitalized , while maintenance and repairs are charged to expense as incurred . when property is retired or .