Fair value is the price that would be received to sell an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. We apply a fair value hierarchy that prioritizes the inputs used to measure fair value:


•	Level 1 inputs are valued using quoted market prices in active markets for identical assets or liabilities. Our Level 1 assets primarily include cash and cash equivalents and mutual funds.

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Level 2 inputs are valued based upon quoted prices for similar instruments in active markets or quoted prices for identical or similar instruments in markets that are not active. Our Level 2 assets are marketable securities, which may consist of certificates of deposit ("CDs"), variable-rate demand notes ("VRDNs"), commercial paper, and restricted investments, which consist of municipal debt securities, corporate debt securities, asset-backed securities, and U.S. agency debentures. Our investments consist of highly rated investment grade debt securities, which are rated A1/P1 or higher for short-term securities and A- or higher for long-term securities, by nationally recognized statistical rating organizations. We obtain our inputs from quoted market prices and independent pricing vendors.


•	Level 3 inputs are generally unobservable and typically reflect management's estimates of assumptions that market participants would use in pricing the asset or liability. We have no Level 3 assets or liabilities.

The carrying value of our accounts receivable, accounts payable and other accrued expenses, and accrued wages and benefits approximates fair value due to their short-term nature. We also hold certain restricted investments, which collateralize workers' compensation programs and are classified as held-to-maturity and carried at amortized cost on our Consolidated Balance Sheets.