U.S. GAAP defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. U.S. GAAP requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value.

We have certain financial assets and liabilities that are measured at fair value on a recurring basis, certain nonfinancial assets and liabilities that may be measured at fair value on a non-recurring basis and certain financial assets and liabilities that are not measured at fair value in our consolidated balance sheets but for which we disclose the fair value. The fair value disclosures of these assets and liabilities are based on a three-level hierarchy, which is defined as follows:

Level 1	Quoted prices in active markets for identical assets or liabilities that the entity can access at the measurement date.
Level 2	Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
Level 3	Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability.

Our marketable debt securities are initially valued at the transaction price and are subsequently remeasured to fair value as of the balance sheet date utilizing third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches and observable market inputs to determine value. Observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers and other industry and economic events. We validate the prices provided by our third-party pricing services by obtaining independent market values from other pricing sources and analyzing pricing data in certain instances.

Our foreign currency exchange contracts are measured at fair value on a recurring basis in our accompanying consolidated balance sheets. We measure the fair value of our foreign currency exchange contracts classified as derivative instruments using an income approach, based on prevailing market forward rates less the contract rate multiplied by the notional amount. The product of this calculation is then adjusted for counterparty risk.

Our interest rate swap agreement in prior years were measured at fair value on a recurring basis in our accompanying consolidated balance sheets. These interest rate swaps were classified as derivative instruments using an income approach, utilizing a discounted cash flow analysis based on the terms of the contract and the interest rate curve adjusted for counterparty risk.

The amount outstanding under our unsecured revolving credit facility and long-term debt are measured at carrying value in our accompanying consolidated balance sheets though we disclose the fair value of these financial instruments. We determine the fair value of the amount outstanding under our credit facility and long-term debt using an income approach, utilizing a discounted cash flow analysis based on current market interest rates for debt issues with similar remaining years to maturity, adjusted for applicable credit risk. Our credit facility and long-term debt are valued using Level 2 inputs. The estimated fair value of our credit facility approximates its carrying value. At December 31, 2017, the estimated fair value and carrying value of our long-term debt were $632.0 million and $606.6 million, respectively. At December 31, 2016, the estimated fair value and carrying value of our long-term debt were $609.5 million and $593.7 million, respectively.