Form S-1 'fable of Contents Blue Buffalo Pet Products, Inc. Notes to Consolidated Financial Statements (Continued) standby letters of credit in the amount of approximately $0.1 million and $0.5 million, respectively. issued by TD Bank. These letters of credit are being maintained as security for performance of certain of the Company's operating lease obligations. The letters of credit are automatically renewed on an annual basis sixty days prior to expiration. Receivables Trade receivables consist of uncollateralized, non-interest bearing customer obligations due under normal trade terms. Other receivables consist primarily of reimbursable amounts due from co-manufacturers for packaging of $7.2 million and $4.4 million and income tax receivables of $7.9 million and $18.2 million at December 31, 2013 and 2014, respectively. We also maintain an allowance for doubtful accounts for estimated losses resulting from the inability of our customers to make payments and other actual and estimated deductions. If the financial condition of our customers were to deteriorate, resulting in an impairment of their ability to make payments, an additional allowance could be required. Past due balances are reviewed individually for collectability. As of December 31, 2013 and 2014, the allowance for doubtful accounts was immaterial. Receivables consisted of the following at December 31: (dollar. Br. ikons:And.) 2013 2014 Trade receivables, net $37,236 $54,647 Oder receivables 15.139 23.973 Total $52.375 $78,620 We are exposed to concentration of credit risk by our customers. Approximately 80% and 72% of gross trade accounts receivable at December 31, 2013 and December 31, 2014. respectively, were from our two large customers. In 2013 and 2014, two customers accounted for 10% or more of our consolidated net sales. Sales to these customers represented 58% and 20% of net sales for the year ended December 31, 2012. 53% and 22% of net sales for the year ended De