Financial instruments and concentration of credit risks	12 Months Ended
Financial instruments and concentration of credit risks	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Financial instruments and concentration of credit risks	Financial instruments and concentration of credit risks Due to its foreign operations, the company is exposed to the effects of foreign currency exchange rate fluctuations on the U.S. dollar, principally related to intercompany account balances. The company uses derivative financial instruments to reduce its exposure to market risks from changes in foreign currency exchange rates on such balances. The company enters into foreign exchange forward contracts, generally having maturities of 3 months or less, which have not been designated as hedging instruments. At December 31, 2016 and 2015, the notional amount of these contracts was $428.9 million and $940.1 million, respectively, and the fair value of such contracts was a net gain of $0.5 million and a net loss of $4.4 million, respectively, of which a gain of $2.4 million and $2.2 million, respectively, has been recognized in “Prepaid expenses and other current assets” and a loss of $1.9 million and $6.6 million, respectively, has been recognized in “Other accrued liabilities.” Changes in the fair value of these instruments was a loss of $29.1 million, a gain of $15.6 million and a gain of $17.3 million, respectively, for years ended December 31, 2016, 2015 and 2014, which has been recognized in earnings in “Other income (expense), net” in the company’s consolidated statements of income. The fair value of these forward contracts is based on quoted prices for similar but not identical financial instruments; as such, the inputs are considered Level 2 inputs. Financial instruments also include temporary cash investments and customer accounts receivable. Temporary investments are placed with creditworthy financial institutions, primarily in money market funds, time deposits and certificate of deposits which may be withdrawn at any time at the discretion of the company without penalty. At December 31, 2016 and 2015, the company’s cash equivalents principally have maturities of less than one month or can be withdrawn at any time at the discretion of the company without penalty. Due to the short maturities of these instruments, they are carried on the consolidated balance sheets at cost plus accrued interest, which approximates market value. Realized gains or losses during 2016, 2015 and 2014, as well as unrealized gains or losses at December 31, 2016 and 2015, were immaterial. Receivables are due from a large number of customers that are dispersed worldwide across many industries. At December 31, 2016 and 2015, the company had no significant concentrations of credit risk with any one customer. At December 31, 2016 and 2015, the company had approximately $74 million and $99 million, respectively, of receivables due from various U.S. federal governmental agencies. At December 31, 2016 and 2015, the carrying amount of cash and cash equivalents approximated fair value. The fair value of long-term debt is based on market prices (Level 2 inputs). At December 31, 2016 and December 31, 2015, the fair value of the company's Senior Notes due 2017, of which a portion was retired in 2016, was $97.8 million and $213.2 million, respectively. At December 31, 2016, the fair value of the company's Convertible Senior Notes due 2021, which were issued in March and April of 2016, was $379.8 million.

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.