Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Allowance for doubtful trade accounts receivable	$ 10,017	$ 9,939
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000us-gaap_CommonStockSharesAuthorized	200,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	80,533,536us-gaap_CommonStockSharesIssued	80,533,536us-gaap_CommonStockSharesIssued
Common stock, shares outstanding	72,038,368us-gaap_CommonStockSharesOutstanding	72,713,920us-gaap_CommonStockSharesOutstanding
Treasury stock, shares	8,495,168us-gaap_TreasuryStockShares	7,819,616us-gaap_TreasuryStockShares

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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