CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 19,083	$ 19,134
Accumulated depreciation	364,124	323,031
Intangible assets, accumulated amortization	$ 114,922	$ 88,098
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000us-gaap_CommonStockSharesAuthorized	120,000,000us-gaap_CommonStockSharesAuthorized
Common stock, issued	84,883,517us-gaap_CommonStockSharesIssued	85,500,037us-gaap_CommonStockSharesIssued
Common stock, outstanding	84,883,517us-gaap_CommonStockSharesOutstanding	85,500,037us-gaap_CommonStockSharesOutstanding

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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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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