Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	May 13, 2011
Condensed Financial Statements, Captions [Line Items]
Allowance for doubtful accounts	5,158	6,004
Treasury stock, shares	22,643,808us-gaap_TreasuryStockShares	22,619,554us-gaap_TreasuryStockShares
Class A common stock
Condensed Financial Statements, Captions [Line Items]
Common stock, par value	0.01	0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	255,280,514	254,997,925
Common stock, shares outstanding	232,636,706	232,378,371
Class C common stock
Condensed Financial Statements, Captions [Line Items]
Common stock, par value	0.01	0.01
Common stock, shares authorized	644,871	644,871
Common stock, shares issued	644,871	644,871
Common stock, shares outstanding	644,871	644,871
7.75% senior notes
Condensed Financial Statements, Captions [Line Items]
Interest on borrowings, per annum	7.75%	7.75%	7.75%

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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Contractual interest rate for funds borrowed, under the debt agreement.

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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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