4.	Financial Instruments

The Corporation’s financial instruments include cash equivalents, accounts receivable, notes receivable, bank overdraft, accounts payable, publicly-registered long-term notes, debentures and other long-term debt.

Cash equivalents are placed primarily in money market funds, money market demand deposit accounts and Eurodollar time deposits. The Corporation’s cash equivalents have original maturities of less than three months. Due to the short maturity of these investments, they are carried on the consolidated balance sheets at cost, which approximates fair value.

4.	Financial Instruments (continued)

Accounts receivable are due from a large number of customers, primarily in the construction industry, and are dispersed across wide geographic and economic regions. However, accounts receivable are more heavily concentrated in certain states (namely, Texas, Colorado, North Carolina, Iowa and Georgia). The estimated fair values of accounts receivable approximate their carrying amounts due to the short-term nature of the receivables.

Notes receivable are classified in the line items Other current assets and Other noncurrent assets on the consolidated balance sheets and are not publicly traded. Management estimates that the fair value of notes receivable approximates the carrying amount due to the variable interest rates of the receivables.

The bank overdraft represents amounts to be funded to financial institutions for checks that have cleared the bank. The estimated fair value of the bank overdraft approximates its carrying value due to the short-term nature of the overdraft.

Accounts payable represent amounts owed to suppliers and vendors. The estimated fair value of accounts payable approximates its carrying amount due to the short-term nature of the payables.

The carrying values and fair values of the Corporation’s long-term debt were $1,779,217,000 and $1,890,319,000, respectively, at June 30, 2016; $1,568,774,000 and $1,625,193,000, respectively, at December 31, 2015; and $1,653,338,000 and $1,729,511,000, respectively, at June 30, 2015. The estimated fair value of the publicly-registered long-term notes was estimated based on Level 1 of the fair value hierarchy using quoted market prices. The estimated fair value of other borrowings, which primarily represents variable-rate debt, was based on Level 2 of the fair value hierarchy using quoted market prices for similar debt instruments, and approximates their carrying amounts as the interest rates reset periodically.