Fair Value Measurement	9 Months Ended
Fair Value Measurement	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair value measurement	Fair value measurement We measure and record in the accompanying condensed consolidated financial statements certain assets and liabilities at fair value. U.S. GAAP establishes a hierarchy for those instruments measured at fair value that distinguishes between market data (observable inputs) and our own assumptions (unobservable inputs). The hierarchy consists of three levels: Level 1 - Quoted market prices in active markets for identical assets or liabilities; Level 2 - Inputs other than Level 1 inputs that are either directly or indirectly observable; and Level 3 - Unobservable inputs developed using our own estimates and assumptions, which reflect those that a market participant would use. Our deferred compensation investments were valued using Level 1 inputs with a fair value of $14.6 million as of December 31, 2017. Our deferred compensation assets were invested in a fixed income mutual fund. During the first quarter of 2018, we liquidated the deferred compensation investment to cover payments made to SERP participants (see Note 6). Cost method investments in private companies are recorded at cost, less impairments, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment. The carrying value of these investments was $24.2 million as of September 30, 2018 and $17.4 million as of December 31, 2017. During the nine months ended September 30, 2018 there were no events or changes in circumstance that suggested an impairment or an observable price change to any of these investments. The cost method investments are classified in Level 3 of the fair value hierarchy. We additionally hold other financial instruments, including cash and cash equivalents, receivables, accounts payable and debt. The carrying amounts for cash and cash equivalents, receivables and accounts payable approximated their fair values. The fair value of our total debt, based on the bid and ask quotes for the related debt (Level 2), totaled $3.06 billion at September 30, 2018, and $3.16 billion at December 31, 2017.

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.