Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 3,488	$ 3,260
Accumulated depreciation	259,980	245,629
Accumulated amortization	$ 22,859	$ 20,545
Common stock, $0.01 par value	$ 0.01	$ 0.01
Common stock shares authorized	100,000us-gaap_CommonStockSharesAuthorized	100,000us-gaap_CommonStockSharesAuthorized
Common stock shares issued	44,822us-gaap_CommonStockSharesIssued	44,689us-gaap_CommonStockSharesIssued
Treasury stock shares	922us-gaap_TreasuryStockShares	862us-gaap_TreasuryStockShares

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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