Financial instruments that potentially subject the Company to concentrations of credit risk are principally cash, cash equivalents, short-term investments, accounts receivable and derivative financial instruments. The Company's policy is to place its cash, cash equivalents and short-term investments in highly-rated financial instruments and institutions. Concentration of credit risk with respect to accounts receivable is mitigated by the diversity of the Company's payers and their dispersion across many different geographic regions, and is limited to certain payers who are large buyers of the Company's services. To reduce risk, the Company routinely assesses the financial strength of these payers and, consequently, believes that its accounts receivable credit risk exposure, with respect to these payers, is limited. While the Company has receivables due from federal and state governmental agencies, the Company does not believe that such receivables represent a credit risk since the related healthcare programs are funded by federal and state governments, and payment is primarily dependent on submitting appropriate documentation. At December 31, 2013 and 2012, receivables due from government payers under the Medicare and Medicaid programs represent approximately 13% and 15%, respectively, of the Company's consolidated net accounts receivable. The portion of the Company's accounts receivable due from patients comprises the largest portion of credit risk. At both December 31, 2013 and 2012, receivables due from patients represent approximately 18% of the Company's consolidated net accounts receivable. The Company applies assumptions and judgments including historical collection experience for assessing collectibility and determining allowances for doubtful accounts for accounts receivable from patients.