CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, reserve for credit losses	$ 38,103	$ 30,207
Property, equipment and capitalized software, accumulated depreciation	312,921	264,928
Accumulated amortization	$ 480,950	$ 392,827
Common stock, par value (in dollars per share)		$ 0.01
Common stock, shares authorized (in shares)	175,000,000	175,000,000
Common stock, shares issued (in shares)	47,528,000	47,352,000
Common stock, shares outstanding (in shares)	43,100,000	43,022,000
Treasury stock, shares (in shares)	4,428,000	4,428,000

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

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Face amount or stated value per share of common stock.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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